CA1090888A - Data buffer retiming circuit - Google Patents
Data buffer retiming circuitInfo
- Publication number
- CA1090888A CA1090888A CA278,442A CA278442A CA1090888A CA 1090888 A CA1090888 A CA 1090888A CA 278442 A CA278442 A CA 278442A CA 1090888 A CA1090888 A CA 1090888A
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- output
- clock
- write
- timing
- read
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F5/00—Methods or arrangements for data conversion without changing the order or content of the data handled
- G06F5/06—Methods or arrangements for data conversion without changing the order or content of the data handled for changing the speed of data flow, i.e. speed regularising or timing, e.g. delay lines, FIFO buffers; over- or underrun control therefor
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J3/00—Time-division multiplex systems
- H04J3/02—Details
- H04J3/06—Synchronising arrangements
- H04J3/062—Synchronisation of signals having the same nominal but fluctuating bit rates, e.g. using buffers
- H04J3/0626—Synchronisation of signals having the same nominal but fluctuating bit rates, e.g. using buffers plesiochronous multiplexing systems, e.g. plesiochronous digital hierarchy [PDH], jitter attenuators
Abstract
DATA BUFFER RETIMING CIRCUIT
by Alvin L. Pachynski, Jr.
ABSTRACT OF THE DISCLOSURE
A data buffer retiming circuit makes use of a plurality of buffer storage cells into which serial bit streams are sequentially written, in order to obtain correction for phase jitter. A write clock signal is derived from the serial bit stream and is used to sequentially write the digits into the cells. A stable clock source is used to provide the basic timing for sequentially reading the bits out from the buffer storage cells, and a logic circuit is used in conjunction therewith to obtain the retimed serial bit stream. The write and read timing signals should have a maximum time separation to allow for maximum correction of phase jitter, and it is critical that the write and read signals should alternate. A monitor and reset circuit compares a selected write signal with a selected read signal and, where a violation of the alternating write-read condition occurs, the circuit resets the write timing and holds it until the read timing has attained a particular state.
by Alvin L. Pachynski, Jr.
ABSTRACT OF THE DISCLOSURE
A data buffer retiming circuit makes use of a plurality of buffer storage cells into which serial bit streams are sequentially written, in order to obtain correction for phase jitter. A write clock signal is derived from the serial bit stream and is used to sequentially write the digits into the cells. A stable clock source is used to provide the basic timing for sequentially reading the bits out from the buffer storage cells, and a logic circuit is used in conjunction therewith to obtain the retimed serial bit stream. The write and read timing signals should have a maximum time separation to allow for maximum correction of phase jitter, and it is critical that the write and read signals should alternate. A monitor and reset circuit compares a selected write signal with a selected read signal and, where a violation of the alternating write-read condition occurs, the circuit resets the write timing and holds it until the read timing has attained a particular state.
Description
~.~3~0 ~3~ L-463 3 Field o~ Invention 4This invention relates to pulse transmission systems and in particular to the retiming of serial bit streams to reduce phase 6 distortion (jitter) introduced by transmission via an imperfect 7 transmission medium.
In prior-art devices, the basic timing information was derived 11 from the serial bit stream itself. Retiming was accomplished by 12 controlling the frequency of a local oscillator by the phase difference 13 between the incoming pulse train and the local oscillator output. Thus, 14 phase jitter was reduced by allowing the local oscillator to smooth out the phase differences in the phase of the incoming bit stream.
16 ~ ~ An improvement over the above-described prior-art technique is 17 disclosed in U. S. Patent 3,093,815, issued June ll, 1963, to M.
18 Karnaugh. In accordance with the invention therein described, coarse 19 retiming is accomplished in much the same manner as is discussed for the above-described prior-art technique. This coarse timing information was 21 utilized to ~rite the successive elements of a serial bit stream into one 22 of a number of the buffer storage cells in a fixed, cyclic order. At a 23 later time, for example half of the period of a storage cycle, this 24 in~ormation was read from the buffer storage elements under the control of a highly stabilized local clock. The clock frequency, and hence the 26 read-out rate, was controlled by a signal representing the average amount 27 of information stored in the buffer storage cells at any partlcular time.
28 Thus, the local clock rate was made responsive to the average amount of 29 data in the buffer storage cells, to prevent an undue accumulation or depletion from the buffer store.
~ 11)91~ tl L-463 1 A principal disadvantage of the patented technique is the
In prior-art devices, the basic timing information was derived 11 from the serial bit stream itself. Retiming was accomplished by 12 controlling the frequency of a local oscillator by the phase difference 13 between the incoming pulse train and the local oscillator output. Thus, 14 phase jitter was reduced by allowing the local oscillator to smooth out the phase differences in the phase of the incoming bit stream.
16 ~ ~ An improvement over the above-described prior-art technique is 17 disclosed in U. S. Patent 3,093,815, issued June ll, 1963, to M.
18 Karnaugh. In accordance with the invention therein described, coarse 19 retiming is accomplished in much the same manner as is discussed for the above-described prior-art technique. This coarse timing information was 21 utilized to ~rite the successive elements of a serial bit stream into one 22 of a number of the buffer storage cells in a fixed, cyclic order. At a 23 later time, for example half of the period of a storage cycle, this 24 in~ormation was read from the buffer storage elements under the control of a highly stabilized local clock. The clock frequency, and hence the 26 read-out rate, was controlled by a signal representing the average amount 27 of information stored in the buffer storage cells at any partlcular time.
28 Thus, the local clock rate was made responsive to the average amount of 29 data in the buffer storage cells, to prevent an undue accumulation or depletion from the buffer store.
~ 11)91~ tl L-463 1 A principal disadvantage of the patented technique is the
2 complexity and, hence, cost of deriving a control signal which represents ~, the average amount of information storsd in the buffer storage cells at any particular instant and i.n using this signal to control the "local clock"
frequency. Such prior-art arrangements employ circuitry which provides 6 for constant write/read comparisons and for frequency adjustment of a voltage-controlled oscillator used as a read clock. It is a purpose of 8 this invention to retain the retiming feature, i.e., phase jitter reduc~ion ~ and fixed phase compensation without the need for constant write/read phase comparison and frequency adjustment of the "read" voltage-controllecl 11 oscillator.
13 SU~RY OF THE INVENTION
14 A retiming circuit for reducing the phase jitter in a serial bit stream generates ~ write timing signals, each having a rate which is 16 l/N that of the serial bit streams. The N write timing signals are used 17 to sequentially write individual bits into one of N buffer storage ceils 18 in a cyclic order. A stable clock source having a rate equal to that of 1~ the serial bit stream is used as a reference for the N read timing signals which sequentially read the individual bits out of the buffer storage cell 21 in retimed serial form.
22 The write/read sequence should alternate, and the maximum 23 possible separation in time should occur between the write/read sequences 24 so as to permit correction of a maximum of phase distortion for each bit.
A monitor and reset circuit compares a selected write timing signal with a 26 selected read timing signal to determine if the alternating write/read 27 sequence has been violated. Violations occur if more than one read timing 28 signal occurs between two sequential write timing si~nals; or, if two 29 write timing signals occur bett~een two sequential read timing signa].s. l~len this happens, the monitor and reset circuit resets one time:r to a first 32 _ ~ _ - ~o~
l predetermined timing signal position and holds it in this condition until 2 the other timer reaches a second predetermined timing signal condition.
BRIEF DESCRIPT_ON OF THE DRAWING
FIG. l is a block diagram showing the interconnection of the 6 basic elements of the invention.
7 FIGc 2 is a more detailed block diagram which illustrates a 8 preferred embodiment of the invention.
9 FIG. 3 is a waveform diagram which shows the retiming process of the preferred embodiment of FIG. 2.
ll FIG. 4 is a block diagram of the digital monitor and reset 12 circuit used in the preferred embodiment of the invention.
l3 FIG. 5 is a waveform diagram which shows the waveforms at 14 pertinent points of FIG. 4 when fw has uniform pulses.~
FIG. 6 is a waveform diagram which shows how the lncoming bit 16 stream is dlgitally retimed by action of the monitor and reset circuit.
17 ~
18 ~ DETAILED DESCRIPTION OF THE INVENTION
19 Referring to FIG. l, the incoming bit stream appears at path 2 ~O and is applied to the buffer storage cells included in block 60 Write 21 clock 4 actually writes the separate bits sequentially into cells of a 22 storage device. The write clock also provides an output to the mon1tor and 23 reset circuit 12. The read clock 8 sequential7y reads the separate bits 24 stored in the individual cells of buffer storage 6 through retiming logic and into the output path 14, providing a retimed output which reduces the 26 phase jitter which occurs at the incoming bit stream on path 2. Read clock27 8 also provides inputs to the monitor and reset circuit 12 which, in 28 combination with the write clock, determines if the write and read timing 29 pulses alternate or if there are occurrences of a plurality of write pulsesintervening between read pulses and/or a plurality of read pulses occurring ,, . ) ~ )O~B~ L-464 1 between adjacen* write pulses. In the latter events, one clock is reset.
In the diagram of FIG. 1, it is the write clock which is reset; however,
frequency. Such prior-art arrangements employ circuitry which provides 6 for constant write/read comparisons and for frequency adjustment of a voltage-controlled oscillator used as a read clock. It is a purpose of 8 this invention to retain the retiming feature, i.e., phase jitter reduc~ion ~ and fixed phase compensation without the need for constant write/read phase comparison and frequency adjustment of the "read" voltage-controllecl 11 oscillator.
13 SU~RY OF THE INVENTION
14 A retiming circuit for reducing the phase jitter in a serial bit stream generates ~ write timing signals, each having a rate which is 16 l/N that of the serial bit streams. The N write timing signals are used 17 to sequentially write individual bits into one of N buffer storage ceils 18 in a cyclic order. A stable clock source having a rate equal to that of 1~ the serial bit stream is used as a reference for the N read timing signals which sequentially read the individual bits out of the buffer storage cell 21 in retimed serial form.
22 The write/read sequence should alternate, and the maximum 23 possible separation in time should occur between the write/read sequences 24 so as to permit correction of a maximum of phase distortion for each bit.
A monitor and reset circuit compares a selected write timing signal with a 26 selected read timing signal to determine if the alternating write/read 27 sequence has been violated. Violations occur if more than one read timing 28 signal occurs between two sequential write timing si~nals; or, if two 29 write timing signals occur bett~een two sequential read timing signa].s. l~len this happens, the monitor and reset circuit resets one time:r to a first 32 _ ~ _ - ~o~
l predetermined timing signal position and holds it in this condition until 2 the other timer reaches a second predetermined timing signal condition.
BRIEF DESCRIPT_ON OF THE DRAWING
FIG. l is a block diagram showing the interconnection of the 6 basic elements of the invention.
7 FIGc 2 is a more detailed block diagram which illustrates a 8 preferred embodiment of the invention.
9 FIG. 3 is a waveform diagram which shows the retiming process of the preferred embodiment of FIG. 2.
ll FIG. 4 is a block diagram of the digital monitor and reset 12 circuit used in the preferred embodiment of the invention.
l3 FIG. 5 is a waveform diagram which shows the waveforms at 14 pertinent points of FIG. 4 when fw has uniform pulses.~
FIG. 6 is a waveform diagram which shows how the lncoming bit 16 stream is dlgitally retimed by action of the monitor and reset circuit.
17 ~
18 ~ DETAILED DESCRIPTION OF THE INVENTION
19 Referring to FIG. l, the incoming bit stream appears at path 2 ~O and is applied to the buffer storage cells included in block 60 Write 21 clock 4 actually writes the separate bits sequentially into cells of a 22 storage device. The write clock also provides an output to the mon1tor and 23 reset circuit 12. The read clock 8 sequential7y reads the separate bits 24 stored in the individual cells of buffer storage 6 through retiming logic and into the output path 14, providing a retimed output which reduces the 26 phase jitter which occurs at the incoming bit stream on path 2. Read clock27 8 also provides inputs to the monitor and reset circuit 12 which, in 28 combination with the write clock, determines if the write and read timing 29 pulses alternate or if there are occurrences of a plurality of write pulsesintervening between read pulses and/or a plurality of read pulses occurring ,, . ) ~ )O~B~ L-464 1 between adjacen* write pulses. In the latter events, one clock is reset.
In the diagram of FIG. 1, it is the write clock which is reset; however,
3 it will become apparent later that either clock may be reset. Further, the write cloc~ timing may be derived from the incoming bit stream. Also, the write clock output may be used as an input to control the clock rate of the 6 read clock so that the average rate of the read clock is equal to the 7 average rate of the write clock. The read and write frequencies are the 8 same, but the phase relationship will vary. It is this effect that is 9 controlled by the subject data bufer so as to minimize phase jitter at 10I the output. This is explained in more detail with respect to FIG. 4.
11¦ Referring now to FIG. 2, an incoming serial bit stream at 12 ¦ rate fw is simultaneously applied to each of the D-inputs of buffer storage13 ¦ 6. In this embodimentJ four D-type flip-flops are used as storage cells, 14 ¦ although it should be understood that more or less cells may be used 15 ¦ depending upon the time interval over which correction is to be obtained.
16 ¦ Also, the incoming bit stream is applied to a data clock recovery circuit 17 ¦ 14 which develops the output frequency fw which is applied to write 18 ¦ counter 16. I~rite counter 16 provides four timed outputs at 1/4 the rate 19 ¦ of clock fw This is shown diagrammatically by waveforms fw and Wl through20 ¦ W4 in FIG. 3 where the designations at the left of the drawing refer to 21 ¦ the actual path and/or output designations as shown on FIG. 2. For example, 22 ¦ Wl is the output 1 from the write counter and also illustrates the path 23 ¦ interconnecting the write counter with the clock pulse input of flip-flop 24 ¦ 18. The Ql output is the output of flip-flop 18 at the Q-output of this 25 ¦ D-type flip-flop. ~hile it ~ou.ld normally be expected that the incoming 26¦ serial bit stream would include phase jitter, none is shown in FIG. 3 in ~71 order that the various relationships of the waveforms may be illustrated 28¦ without adding this complexity. The incoming serial bi~ stream is 2~1 sequentially gated by the write pulses from a counter such as a ring counter 3~1 - 5 -10'~0~
1 into the cells 18, 20, 22, and 24~ As illustrated in FIG. 3, the 2 incoming pulses are stored for a period of four pulse periods as 3 illustrated by waveforms Ql - Q4. Thus, the data bit of any one cell
11¦ Referring now to FIG. 2, an incoming serial bit stream at 12 ¦ rate fw is simultaneously applied to each of the D-inputs of buffer storage13 ¦ 6. In this embodimentJ four D-type flip-flops are used as storage cells, 14 ¦ although it should be understood that more or less cells may be used 15 ¦ depending upon the time interval over which correction is to be obtained.
16 ¦ Also, the incoming bit stream is applied to a data clock recovery circuit 17 ¦ 14 which develops the output frequency fw which is applied to write 18 ¦ counter 16. I~rite counter 16 provides four timed outputs at 1/4 the rate 19 ¦ of clock fw This is shown diagrammatically by waveforms fw and Wl through20 ¦ W4 in FIG. 3 where the designations at the left of the drawing refer to 21 ¦ the actual path and/or output designations as shown on FIG. 2. For example, 22 ¦ Wl is the output 1 from the write counter and also illustrates the path 23 ¦ interconnecting the write counter with the clock pulse input of flip-flop 24 ¦ 18. The Ql output is the output of flip-flop 18 at the Q-output of this 25 ¦ D-type flip-flop. ~hile it ~ou.ld normally be expected that the incoming 26¦ serial bit stream would include phase jitter, none is shown in FIG. 3 in ~71 order that the various relationships of the waveforms may be illustrated 28¦ without adding this complexity. The incoming serial bi~ stream is 2~1 sequentially gated by the write pulses from a counter such as a ring counter 3~1 - 5 -10'~0~
1 into the cells 18, 20, 22, and 24~ As illustrated in FIG. 3, the 2 incoming pulses are stored for a period of four pulse periods as 3 illustrated by waveforms Ql - Q4. Thus, the data bit of any one cell
4 is available to be read out for a total time of four clock periods. This allows jitter and delay variations of much greater than one clock period 6 and, in fact, can theoretically approach four clock periods in duration.
7 Read clock 8 is shown as comprising a master clock 26 having a 8 frequency fr, which frequency would nominally be equal to ~w The 9 master clock applies the fr timing frequency to the read counter which provides the four read timing outputs Rl through R4 to read the data 11 out from the individual storage cells. Although the data clock 14 and 12 the naster clock 26 are shown as being independent, they must be at the 13 same frequency, but may vary in their phase relationship, i.e., jitter 14 and fixed phase difference. In FIG. 3, they are shown to be at the same frequency and phase. However, the phase relationship for the read 16 counter outputs is such as to give the optimum phase relationship between 17 the read a~nd write counters. This is shown by the cyclic notation within 1~ the clock pulses of the fw and fr waveforms.
19 As shown in FIG. 3, the data bit is written into cell 18 on the positive transition of the leading edge of the read pulse Wl. A time delay 21 is not illustrate~ between the data clock frequency positive transition and 2~ the read pulse outputs Wl - W4. This delay was not shown because there 23 is no requirement to establish a particular phase delay relationship between 24 the data clock frequency fw and the write pulse, Howe~er, with respect to the master c1ack 26 output frequency fr~ it is importan~ that the delay be 26 shown, and this is illustrated by a shift of the read output Rl as 27 illustrated in FIG. 3. The Ql bit ;s read out by the read clock pulse 28 Rl, and it should be noted that this occurs ju$t subsequent to the clock pulse 29 which generates the R~ read pulse. Because of the coincidence of the Ql ~3 10~()8~3 I L-~64 1 and Rl inputs to AND-gate 30, the Ql output appears on path 39 as 2 ¦ illustrated in FIG. 3. Since the readout of flip-flop 40 will not occur 3 ¦ until the next input clock pulse from master clock 26, the serialized a ¦ output is delayed as illustrated in FIG. 3 at 14. Note that the relationship 51 between the serialized output and the stored pulse in cell 18 is such 6¦ that this occurs at the middle of the storage interval. This then ¦ illustrates an optimum relationship betw~en the write and read pulse ~¦ occurrences.
9 ¦ In the circuit shown in FIG. 2, a master clock may be used to lO ¦ provide the fw and fr clock pulses for operating both the write and read ll ¦ counters. In this case, they will run synchronously but with a fixed and 12 ¦ unpredictable phase relationship. For example, while data are being written 13 ¦ into cell 1~, the read counter could be reading any one of the four cells.
14 ¦ In order to allow maximum phase jitter, in this case, the read counter ~5 ¦ should be reading out of cell no. 22. This write/read relationship is 16 ¦ as illustrated in FIG. 3. However, it is possible, even in this case, 17 ¦ that the read counter could be reading out from a memory cell at the same 18 ¦ instant in time that the cell is being written into. This could produce errors.
19 ¦ To ensure optimum phasing between the write and read counters, it is 20 ¦ necessary that a technique be provided that will reset one or both of these 21 ¦ counters to achieve this optimum phase relationship. In the block 22 ¦ diagrams of FIGS. l and 2, this is shown as a monitor and reset 12. The 23 ¦ monitor and reset circuit is shown in more detail in FIG. 4.
24 ¦ The monitor and reset circuit 12, illustrated in FIG. 4, compares 25 ¦ the write OtltpUt ~1 from path 42 with the read counter output Rl over path 2~ ¦ 44 to ensure that there are never two consecutive write pulses or read 27 ¦ pulses for an individual memory cell without an intervening read or write 28 ¦ pulse therebetween. In other words, the write and read pulses for any 29 ¦ cell must orm an alternating sequence. The ~rite ~1 pLIlse is applied 3l I _ 7 _ 32 ~
~ ' ~.~)9~
L-~6 l simultaneously to the R-input of the R-S flip-flop and to the clock pulse 2 input of D-type flip-flop 58. The Rl input from read counter 28 is 3 inverted in inverter 52, and the output of 52 is applied simultaneously 4 to the S-inpu~ of R-S flip-flop 5~ and to the clock pulse input of D-type flip-flop 60. The R-S flip-flop S~ is toggled only by the positive-going ~ ed~e of the R and S inputs. FIG. 5 illustrates the normal relationship 7 for an optimum write-read phase relationship such as is ~hown in FIG 3.
Note that in this case the write pulse Wl, when applied to flip-flop 54 9 and to flip-flop 58, provides a 1 output on lead 62. This occurs because the Rl has reset flip-flop 54, causing its Q-output OJI lead 56, and thus ll the input at D of flip-flop 58, to be a 1 prior to the occurrence of the 12 write pulse Wl. When the write pulse Wl appears at a later time, this is l~ read through to the Q-output, and thus the continuous output on lead 62 l~ is a 1. Similarly, the output on lead 6~ from flip-flop 60 is a 1, and 15~ thus the output of NAND-gate 66 is a 0, which is applied via lead 48 to 16 the reset input of write counter 16. Thus, nothing occurs so far as the 17 write counter 16 is concerned.
18 However, it is possi~le for the phase relationships between 19 fw and fr to shift such that the bit in memory cell 18, for example, is being read out just prior to the time that new data is being written into 21 that memory cell. This is acceptable as long as the read clock Rl does 2Z not shift to the right. If this happens, clue for example to phase jitter in the write clock, a data error will result. This is illustrated 2~s graphically in the waveform diagram of FIG. 6. The bit Ql of cell 18, at 2~ time interval A, is being read just prior to the time that new data would 26 be inserted into this buffer storage cell. However, at time period B, the 27 write clock has shifted slightly to the left with respect to read clock, 28 and as a result Rl does not sample da-ta bit B in cell lS. This produces 31 a data bit omi~sion, i.e., error iJI the data buf:Eer output. 'Ille monitor 10~0~8B L-464 1 and reset circuit detects this as follows. Referring to ~IG. 6, just prior 2 to f clock pulse position no. 1 (see nu~erical designation above fw), the 3 Rl provides a positive transition to the input S of flip-flop 54, thus 4 causing a 1 output on lead 56. lYhen the write pulse Wl is applied to the R-input o~ flip-flop 54 shortly thereafter, the output does not i~nediately 6 change. Thus, the simultaneous application o-f write pulse Wl to the clock 7 pulse input of flip-flop 58 reads a l output on lead 62. Shortly thereafter, 8 the output on lead 56 goes to zero, and therefore a short pulse is formed 9 as illustrated in FIG. 6 at line S6. This occurs again at fw pulse position 5, but does not occur at fw pulse position 9 because o~ the ll phase shift in clock fw. This will be discussed in more detail hereinbelow.
12 With respect to flip-flop 60, it is apparent that the D-input is 0 at the time 13 of occurrence of the next positive transition of Rl. Thus, the Q-output 14 is a l on path 64 and is illustrated in FIG. 6 at 64. The two logic 1 lS inputs to NA~D-gate 66 again provide a 0 output on path 48 and, thus 16 reset the input of write counter 16.
17 If, for example, Wl and Rl do not alternate, the following 18 occurs. Referring to FIG 6, the B time interval of Ql~ the write pulse Wl l9 has shifted in phase such that there are two consecutive Wl pulses without an Rl pulse between them. Since the Wl pulse that started time period B
21 has not been followed by a Rl pulse, lead 56 is still at logic 0. The ~2 next Wl pulse ~f clock cycle 9) clocks the 0 from lead 56 into flip-flop 23 58, which generates a 0 at its output 62. Thus, the inputs to NAND-gate 66 24 are 1 and 0, and therefore a 1 output appears on lead 48, which is applied to the reset input of write counter 16. This causes write counter 16 to be 26 reset to count W4 where it is held until the start of a read-count input R3 27 on path 46 to the S ~Set) and C (Clear) inputs of flip-flops 58 and 60, .
2~ respectively. At this time, leads 62 and 64 both become logic l and the 29 write counter 16 begins counting again, starting with Wl As can be seen ;~iO
~2 - 9 -10~(~8t3~ L-46d 1 ¦ from the waveform diagrams of FIG. 6, in this example, the negative-going 2 ¦ edge of the read pulse Rl is now centered with respect to the time interval 3 ¦ of cell 22, i.e., the phase relationship between the write and read timing 4 ¦ signals has been reset to the optimum condition. If there are two 51 consecutive 21 pulses, without a Wl pulse between, flip-flop 60 operates ~¦ in the same manner as described hereinabove for flip-flop 58.
7 ¦ While the invention has been particularly shown and described 8 ¦with reference to a preferred embodiment thereof, it will be understood 9 ¦by those skilled in the art t'nat changes in form and detail may be made 12 wit ~ut departing from the spirit and scope oE the invention.
8 ::
2~ .
32 - lO -
7 Read clock 8 is shown as comprising a master clock 26 having a 8 frequency fr, which frequency would nominally be equal to ~w The 9 master clock applies the fr timing frequency to the read counter which provides the four read timing outputs Rl through R4 to read the data 11 out from the individual storage cells. Although the data clock 14 and 12 the naster clock 26 are shown as being independent, they must be at the 13 same frequency, but may vary in their phase relationship, i.e., jitter 14 and fixed phase difference. In FIG. 3, they are shown to be at the same frequency and phase. However, the phase relationship for the read 16 counter outputs is such as to give the optimum phase relationship between 17 the read a~nd write counters. This is shown by the cyclic notation within 1~ the clock pulses of the fw and fr waveforms.
19 As shown in FIG. 3, the data bit is written into cell 18 on the positive transition of the leading edge of the read pulse Wl. A time delay 21 is not illustrate~ between the data clock frequency positive transition and 2~ the read pulse outputs Wl - W4. This delay was not shown because there 23 is no requirement to establish a particular phase delay relationship between 24 the data clock frequency fw and the write pulse, Howe~er, with respect to the master c1ack 26 output frequency fr~ it is importan~ that the delay be 26 shown, and this is illustrated by a shift of the read output Rl as 27 illustrated in FIG. 3. The Ql bit ;s read out by the read clock pulse 28 Rl, and it should be noted that this occurs ju$t subsequent to the clock pulse 29 which generates the R~ read pulse. Because of the coincidence of the Ql ~3 10~()8~3 I L-~64 1 and Rl inputs to AND-gate 30, the Ql output appears on path 39 as 2 ¦ illustrated in FIG. 3. Since the readout of flip-flop 40 will not occur 3 ¦ until the next input clock pulse from master clock 26, the serialized a ¦ output is delayed as illustrated in FIG. 3 at 14. Note that the relationship 51 between the serialized output and the stored pulse in cell 18 is such 6¦ that this occurs at the middle of the storage interval. This then ¦ illustrates an optimum relationship betw~en the write and read pulse ~¦ occurrences.
9 ¦ In the circuit shown in FIG. 2, a master clock may be used to lO ¦ provide the fw and fr clock pulses for operating both the write and read ll ¦ counters. In this case, they will run synchronously but with a fixed and 12 ¦ unpredictable phase relationship. For example, while data are being written 13 ¦ into cell 1~, the read counter could be reading any one of the four cells.
14 ¦ In order to allow maximum phase jitter, in this case, the read counter ~5 ¦ should be reading out of cell no. 22. This write/read relationship is 16 ¦ as illustrated in FIG. 3. However, it is possible, even in this case, 17 ¦ that the read counter could be reading out from a memory cell at the same 18 ¦ instant in time that the cell is being written into. This could produce errors.
19 ¦ To ensure optimum phasing between the write and read counters, it is 20 ¦ necessary that a technique be provided that will reset one or both of these 21 ¦ counters to achieve this optimum phase relationship. In the block 22 ¦ diagrams of FIGS. l and 2, this is shown as a monitor and reset 12. The 23 ¦ monitor and reset circuit is shown in more detail in FIG. 4.
24 ¦ The monitor and reset circuit 12, illustrated in FIG. 4, compares 25 ¦ the write OtltpUt ~1 from path 42 with the read counter output Rl over path 2~ ¦ 44 to ensure that there are never two consecutive write pulses or read 27 ¦ pulses for an individual memory cell without an intervening read or write 28 ¦ pulse therebetween. In other words, the write and read pulses for any 29 ¦ cell must orm an alternating sequence. The ~rite ~1 pLIlse is applied 3l I _ 7 _ 32 ~
~ ' ~.~)9~
L-~6 l simultaneously to the R-input of the R-S flip-flop and to the clock pulse 2 input of D-type flip-flop 58. The Rl input from read counter 28 is 3 inverted in inverter 52, and the output of 52 is applied simultaneously 4 to the S-inpu~ of R-S flip-flop 5~ and to the clock pulse input of D-type flip-flop 60. The R-S flip-flop S~ is toggled only by the positive-going ~ ed~e of the R and S inputs. FIG. 5 illustrates the normal relationship 7 for an optimum write-read phase relationship such as is ~hown in FIG 3.
Note that in this case the write pulse Wl, when applied to flip-flop 54 9 and to flip-flop 58, provides a 1 output on lead 62. This occurs because the Rl has reset flip-flop 54, causing its Q-output OJI lead 56, and thus ll the input at D of flip-flop 58, to be a 1 prior to the occurrence of the 12 write pulse Wl. When the write pulse Wl appears at a later time, this is l~ read through to the Q-output, and thus the continuous output on lead 62 l~ is a 1. Similarly, the output on lead 6~ from flip-flop 60 is a 1, and 15~ thus the output of NAND-gate 66 is a 0, which is applied via lead 48 to 16 the reset input of write counter 16. Thus, nothing occurs so far as the 17 write counter 16 is concerned.
18 However, it is possi~le for the phase relationships between 19 fw and fr to shift such that the bit in memory cell 18, for example, is being read out just prior to the time that new data is being written into 21 that memory cell. This is acceptable as long as the read clock Rl does 2Z not shift to the right. If this happens, clue for example to phase jitter in the write clock, a data error will result. This is illustrated 2~s graphically in the waveform diagram of FIG. 6. The bit Ql of cell 18, at 2~ time interval A, is being read just prior to the time that new data would 26 be inserted into this buffer storage cell. However, at time period B, the 27 write clock has shifted slightly to the left with respect to read clock, 28 and as a result Rl does not sample da-ta bit B in cell lS. This produces 31 a data bit omi~sion, i.e., error iJI the data buf:Eer output. 'Ille monitor 10~0~8B L-464 1 and reset circuit detects this as follows. Referring to ~IG. 6, just prior 2 to f clock pulse position no. 1 (see nu~erical designation above fw), the 3 Rl provides a positive transition to the input S of flip-flop 54, thus 4 causing a 1 output on lead 56. lYhen the write pulse Wl is applied to the R-input o~ flip-flop 54 shortly thereafter, the output does not i~nediately 6 change. Thus, the simultaneous application o-f write pulse Wl to the clock 7 pulse input of flip-flop 58 reads a l output on lead 62. Shortly thereafter, 8 the output on lead 56 goes to zero, and therefore a short pulse is formed 9 as illustrated in FIG. 6 at line S6. This occurs again at fw pulse position 5, but does not occur at fw pulse position 9 because o~ the ll phase shift in clock fw. This will be discussed in more detail hereinbelow.
12 With respect to flip-flop 60, it is apparent that the D-input is 0 at the time 13 of occurrence of the next positive transition of Rl. Thus, the Q-output 14 is a l on path 64 and is illustrated in FIG. 6 at 64. The two logic 1 lS inputs to NA~D-gate 66 again provide a 0 output on path 48 and, thus 16 reset the input of write counter 16.
17 If, for example, Wl and Rl do not alternate, the following 18 occurs. Referring to FIG 6, the B time interval of Ql~ the write pulse Wl l9 has shifted in phase such that there are two consecutive Wl pulses without an Rl pulse between them. Since the Wl pulse that started time period B
21 has not been followed by a Rl pulse, lead 56 is still at logic 0. The ~2 next Wl pulse ~f clock cycle 9) clocks the 0 from lead 56 into flip-flop 23 58, which generates a 0 at its output 62. Thus, the inputs to NAND-gate 66 24 are 1 and 0, and therefore a 1 output appears on lead 48, which is applied to the reset input of write counter 16. This causes write counter 16 to be 26 reset to count W4 where it is held until the start of a read-count input R3 27 on path 46 to the S ~Set) and C (Clear) inputs of flip-flops 58 and 60, .
2~ respectively. At this time, leads 62 and 64 both become logic l and the 29 write counter 16 begins counting again, starting with Wl As can be seen ;~iO
~2 - 9 -10~(~8t3~ L-46d 1 ¦ from the waveform diagrams of FIG. 6, in this example, the negative-going 2 ¦ edge of the read pulse Rl is now centered with respect to the time interval 3 ¦ of cell 22, i.e., the phase relationship between the write and read timing 4 ¦ signals has been reset to the optimum condition. If there are two 51 consecutive 21 pulses, without a Wl pulse between, flip-flop 60 operates ~¦ in the same manner as described hereinabove for flip-flop 58.
7 ¦ While the invention has been particularly shown and described 8 ¦with reference to a preferred embodiment thereof, it will be understood 9 ¦by those skilled in the art t'nat changes in form and detail may be made 12 wit ~ut departing from the spirit and scope oE the invention.
8 ::
2~ .
32 - lO -
Claims (7)
1. Apparatus for retiming a serial bit stream which comprises:
a first timing means providing N sequentially timed outputs, each at a rate which is 1/Nth that of the bit rate of said serial bit stream, means for sequentially storing N binary digits, each said digit being written into said storing means by one of said N timed outputs from the first timing means;
a second timing means including a clock means having an output which provides a clock rate at substantially the bit rate of said serial bit stream and having N sequentially timed outputs, each at a rate which is 1/Nth of said clock rate;
logic means responsive to said second timing means for sequentially reading out the binary digits from said storage means; and monitoring means having one input connected to monitor one of the N sequential timed outputs of said first timing means, having second and third inputs connected to monitor two of the N timed outputs of said second timing means to determine if the write-read inputs alternate and to provide an output signal which resets the N sequential outputs of one said timing means in the event the write-read sequence does not alternate.
a first timing means providing N sequentially timed outputs, each at a rate which is 1/Nth that of the bit rate of said serial bit stream, means for sequentially storing N binary digits, each said digit being written into said storing means by one of said N timed outputs from the first timing means;
a second timing means including a clock means having an output which provides a clock rate at substantially the bit rate of said serial bit stream and having N sequentially timed outputs, each at a rate which is 1/Nth of said clock rate;
logic means responsive to said second timing means for sequentially reading out the binary digits from said storage means; and monitoring means having one input connected to monitor one of the N sequential timed outputs of said first timing means, having second and third inputs connected to monitor two of the N timed outputs of said second timing means to determine if the write-read inputs alternate and to provide an output signal which resets the N sequential outputs of one said timing means in the event the write-read sequence does not alternate.
2. Apparatus in accordance with claim 1 wherein said first timing means further comprises:
a second clock means having a clock pulse repetition rate which is equal to the bit rate of the incoming bit stream and providing a clock pulse output at said rate; and a first counting means having an input connected to the output of said second clock means, said counting means providing N outputs, each providing a timing signal at 1/Nth of the bit rate.
a second clock means having a clock pulse repetition rate which is equal to the bit rate of the incoming bit stream and providing a clock pulse output at said rate; and a first counting means having an input connected to the output of said second clock means, said counting means providing N outputs, each providing a timing signal at 1/Nth of the bit rate.
3. Apparatus in accordance with claim 2 wherein said sequential storing means further comprises:
N memory cells, each having two inputs and an output, one said input of each cell being connected to receive said bit stream and the second input being connected to one of said N outputs of said first counting means.
N memory cells, each having two inputs and an output, one said input of each cell being connected to receive said bit stream and the second input being connected to one of said N outputs of said first counting means.
4. Apparatus in accordance with claim 3 wherein said clock means of said second timing means comprises a stable master clock having a clock pulse repetition rate which is equal to that of said second clock means.
5. Apparatus in accordance with claim 4 wherein said second timing means further comprises:
a second counting means having an input connected to the output of said master clock, said counting means having N outputs, each providing a timing signal at 1/Nth of the master clock rate.
a second counting means having an input connected to the output of said master clock, said counting means having N outputs, each providing a timing signal at 1/Nth of the master clock rate.
6. Apparatus in accordance with claim 5 wherein said logic means further comprises:
N AND-gates, each having two inputs and an output, one said input being connected to one said output of one said memory cell, and the second said input being connected to one of said N outputs of said second counting means;
an OR-gate having N inputs and an output, each input being connected to one said AND-gate output; and retiming means having one input connected to the output of said OR-gate and a second input connected to the output of said master clock whereby the bit stream is retimed.
N AND-gates, each having two inputs and an output, one said input being connected to one said output of one said memory cell, and the second said input being connected to one of said N outputs of said second counting means;
an OR-gate having N inputs and an output, each input being connected to one said AND-gate output; and retiming means having one input connected to the output of said OR-gate and a second input connected to the output of said master clock whereby the bit stream is retimed.
7. Apparatus in accordance with claim 6 wherein said monitoring means further comprises:
means for comparing a selected output from said first counting means with a selected output from said second counting means to determine if there is an alternating sequence; and means for resetting said first counting means when said alternating sequence is violated.
means for comparing a selected output from said first counting means with a selected output from said second counting means to determine if there is an alternating sequence; and means for resetting said first counting means when said alternating sequence is violated.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US687,979 | 1976-05-20 | ||
| US05/687,979 US4054747A (en) | 1976-05-20 | 1976-05-20 | Data buffer |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1090888A true CA1090888A (en) | 1980-12-02 |
Family
ID=24762624
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA278,442A Expired CA1090888A (en) | 1976-05-20 | 1977-05-16 | Data buffer retiming circuit |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | US4054747A (en) |
| CA (1) | CA1090888A (en) |
Families Citing this family (19)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4175287A (en) * | 1978-01-23 | 1979-11-20 | Rockwell International Corporation | Elastic store slip control circuit apparatus and method for preventing overlapping sequential read and write operations |
| US4171538A (en) * | 1978-01-23 | 1979-10-16 | Rockwell International Corporation | Elastic store slip circuit apparatus for preventing read and write operations interference |
| JPS6024613B2 (en) * | 1980-03-10 | 1985-06-13 | 日本電気株式会社 | data transmission equipment |
| DE3044620A1 (en) * | 1980-11-27 | 1982-07-08 | Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt | DIGITAL NEWS TRANSMISSION SYSTEM |
| US4510581A (en) * | 1983-02-14 | 1985-04-09 | Prime Computer, Inc. | High speed buffer allocation apparatus |
| US4542504A (en) * | 1983-08-22 | 1985-09-17 | At&T Bell Laboratories | Shared data receiver |
| US4692894A (en) * | 1984-12-18 | 1987-09-08 | Advanced Micro Devices, Inc. | Overflow/Underflow detection for elastic buffer |
| US4748588A (en) * | 1985-12-18 | 1988-05-31 | International Business Machines Corp. | Fast data synchronizer |
| FR2593337A1 (en) * | 1986-01-23 | 1987-07-24 | Berlinet Denis | Device for synchronising a binary signal with elimination of jitter |
| US4718074A (en) * | 1986-03-25 | 1988-01-05 | Sotas, Inc. | Dejitterizer method and apparatus |
| US4847873A (en) * | 1986-06-13 | 1989-07-11 | Victor Company Of Japan, Ltd. | Interface circuit |
| US4881242A (en) * | 1986-09-09 | 1989-11-14 | Siemens Aktiengesellschaft | Circuit arrangement for the transmission of data signals |
| US4989221A (en) * | 1987-03-30 | 1991-01-29 | Codex Corporation | Sample rate converter |
| US4949361A (en) * | 1989-06-26 | 1990-08-14 | Tektronix, Inc. | Digital data transfer synchronization circuit and method |
| GB9008932D0 (en) * | 1990-04-20 | 1990-06-20 | British Broadcasting Corp | Synchronisation of digital audio signals |
| US5706299A (en) * | 1992-05-21 | 1998-01-06 | Alcatel Network Systems, Inc. | Sonet tributary ambiguity resolution for elastic store control |
| JPH10327158A (en) * | 1997-05-23 | 1998-12-08 | Oki Electric Ind Co Ltd | Clock reproducing device |
| JP4193284B2 (en) * | 1999-05-28 | 2008-12-10 | 沖電気工業株式会社 | Elastic and integrated circuits |
| US7151813B2 (en) * | 2002-07-17 | 2006-12-19 | Intel Corporation | Techniques to reduce transmitted jitter |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1195899A (en) * | 1967-11-21 | 1970-06-24 | Mini Of Technology | Improvements in or relating to Synchronising Arrangements in Digital Communications Systems. |
| FR2137445B1 (en) * | 1971-05-11 | 1973-06-29 | Siemens Ag | |
| US3867579A (en) * | 1973-12-21 | 1975-02-18 | Bell Telephone Labor Inc | Synchronization apparatus for a time division switching system |
-
1976
- 1976-05-20 US US05/687,979 patent/US4054747A/en not_active Expired - Lifetime
-
1977
- 1977-05-16 CA CA278,442A patent/CA1090888A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| US4054747A (en) | 1977-10-18 |
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