CN101425792B - Bi-quad unit for negative feedback type hybrid integrator - Google Patents

Abstract

The invention discloses a double second-order unit of a mixed integrator of a negative feedback type, which comprises a first-stage transconductor, a second-stage source-pole-based tracker integrator, a feedback transistor and a current source, wherein the first-stage transconductor comprises two PMOS transistors and a capacitor and is used for receiving a voltage signal and converting the voltage signal into a current signal to charge the capacitor to form a first-stage integrator, the second-stage source-pole-based tracker integrator comprises two PMOS transistors and a capacitor and is used for converting a voltage signal outputted by the first-stage integrator into a current signal to charge the capacitor to form a second-stage integrator, the feedback transistor comprises two NMOS transistors and is used for integrating plural poles with the two integrators and controlling the output of common mode voltage, and the current source is used for providing the branch current of the double second-order unit. The double second-order unit of a mixed integrator of a negative feedback type is used for realizing the high-order analog filer by the stage linking design method. The structure needs no common-mode feedback circuit and can also realize a DC gain higher than 0dB.

Description

A kind of double-two-order unit of negative feedback type hybrid integrator

Technical field

The present invention relates to the Design of Analog Filter field, particularly a kind of double-two-order unit of negative feedback type hybrid integrator.

Background technology

The notion of filter is at first to be proposed in 1915 by the G.Campbell of the U.S. and German K.Wagner the earliest.Even to this day, the theory and technology of filter is constantly improved and is innovated.Filtering is a kind of frequency-selecting process in fact, thereby filter is a kind of input signal to be carried out the frequency-selective network that frequency specific processing obtains hoping to export signal.According to input signal time domain characteristics, filter can be divided into analog filter and digital filter.Because analog filter has outstanding features such as processing speed is fast, circuit structure is simple, power consumption is little, makes it in various electronic equipments, have duty to use widely.

In the last few years, along with the develop rapidly of wireless communication technology and the continuous progress of CMOS technology, realized that wireless communication transceiver and the integrated of digital baseband circuit system single chip were the inexorable trends of future development.Integrated on the sheet of analog filter is problem of needing solution badly in the SOC(system on a chip) development.Nineteen eighty-three, Hanu and Tsividis have proposed the active filter of fully integrated MOSFET and electric capacity, have opened the prelude of fully integrated continuous time filter development.Kharramabadi and Gray have proposed to adopt mutual conductance-electric capacity (Gm-C) filter of CMOS technology first, and wherein, trsanscondutance amplifier (Gm) is the amplifier that input voltage signal is converted into current signal.From then on, being integrated with mutual conductance-electric capacity (Gm-C) active filter of being made up of trsanscondutance amplifier and electric capacity in the source filter on the sheet is hot research direction in the Design of Analog Filter field.The Gm-C active filter has the advantages that high frequency characteristics is good, tunability strong, the circuit synthesis ability is good.Be that a single order fully differential Gm-C integrator is formed integrator by transistor transconductance (Gm1) and load capacitance shown in Fig. 1, its transfer function is:

$H\left(s\right)=\frac{{\mathrm{<figure-callout\; id="1"\; label="G\; m"\; filenames="H2008102271286E00041.png"\; state="\{\{state\}\}">G</figure-callout>}}_m}{\mathrm{sg}{C}_L}---\left(1\right)$

D ' Amico is at list of references " Stefano D ' Amico; Matteo Conta and Andrea Baschirotto; " A 4.1-mW 10-MHz Fourth-Order Source-Follower-Based Continuous-Time Filter With 79-dB DR; " IEEE Journal of Solid-State Circuits, pp.2713-2719, Dec.2006 " in described based on the active filter of source follower and broken traditional active filter project organization.A single order is formed integrator based on the source follower integrator by source follower mutual conductance (Gm1) and load capacitance shown in Fig. 2, and its transfer function is:

$H\left(s\right)=\frac{G_{m1}}{G_{m1}+\mathrm{sg}{C}_L}---\left(2\right)$

Usually, second-order low-pass filter (low pass double-two-order unit) transfer function is following:

$H\left(s\right)=\frac{K{\mathrm{\&omega;}}_0^2}{{\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="H2008102271286E00021.png,H2008102271286E00031.png"\; state="\{\{state\}\}">s</figure-callout>}}^2+\frac{{\mathrm{\&omega;}}_0}{Q_0}s+{\mathrm{\&omega;}}_0^2}---\left(3\right)$

Can know in the formula (3) that the low pass double-two-order unit will have plural limit, therefore require will to have in the transistor level double-two-order unit can comprehensive plural limit circuit structure.The full PMOS double-two-order unit based on source follower that D ' Amico proposes all is to adopt the comprehensive plural limit of local positive feedback with full NMOS double-two-order unit, and this method attrition voltage remaining makes this structure be difficult under the low supply voltage and uses.The low pass double-two-order unit is mainly used in adopting in the cascade method design high-order low-pass filter.In cascade method design high-order low-pass filter, the input and output common mode electrical level of the low pass double-two-order unit that is adopted is identical to be easy to use the direct cascade of identical low pass double-two-order unit to realize high-order low-pass filter.The relevant knowledge of relevant active filter can be with reference to Deliyannis, T., and Sun, Y., and Fidler, J., K.: ' Continuous-Time Active Filter Design ' Boca Raton, FL:CRC, 1999.

Above-mentionedly be used to realize that the fully differential Gm-C double-two-order unit of Gm-C active power filtering is as shown in Figure 1; This double-two-order unit requires extra common mode feedback circuit; Detect output common mode voltage, feedback signal is regulated the electric current of current source (Ib) to stablize output common mode voltage, has so just consumed more power consumption.List of references " Stefano D ' Amico; Matteo Conta and Andrea Baschirotto; " A 4.1-mW 10-MHzFourth-Order Source-Follower-Based Continuous-Time Filter With 79-dBDR; " IEEE Journal of Solid-State Circuits; Pp.2713-2719; Dec.2006 " the quadravalence low pass filter described is realized by two low pass double-two-order unit cascades, but full PMOS double-two-order unit is unequal with the input common mode electrical level of full NMOS double-two-order unit, so will adopt full PMOS double-two-order unit can not be only to realize quadravalence low pass filter or can not be with full NMOS double-two-order unit cascade realization quadravalence low pass filter with full PMOS double-two-order unit cascade with full NMOS double-two-order unit cascade.If the full PMOS double-two-order unit based on source follower that adopts D ' Amico to propose is realized more high-order low-pass filter with full NMOS double-two-order unit, must adopt full PMOS double-two-order unit to replace cascade and could satisfy the requirement of inter-stage common mode with full NMOS double-two-order unit.

Fully differential Gm-C low pass double-two-order unit input and output common mode electrical level is identical at present is easy to direct cascade realization high-order low-pass filter, but needs common mode feedback circuit to consume extra power consumption.Some problems that exist based on the full PMOS double-two-order unit of source follower and full NMOS double-two-order unit: (1) does not need common-mode feedback based on the full PMOS double-two-order unit of source follower with full NMOS double-two-order unit, must replace the cascade employing and satisfies the requirement of inter-stage common mode but the input and output common mode electrical level is unequal; (2) list of references " Stefano D ' Amico; Matteo Conta and Andrea Baschirotto; " A 4.1-mW 10-MHzFourth-Order Source-Follower-Based Continuous-Time Filter With 79-dBDR; " IEEE Journal of Solid-State Circuits, pp.2713-2719, Dec.2006 " full PMOS double-two-order unit does not have gain loss in the quadravalence low pass filter described; And full NMOS double-two-order unit has the 3.5dB gain loss, and the double-two-order unit gain of this kind structure can not be greater than 0dB.

At present full PMOS double-two-order unit is to adopt internal positive feedback to stablize the output common mode level with full NMOS double-two-order unit, and the technology that adopts negative feedback to stablize the output common mode level also is not applied in the low pass double-two-order unit.

Summary of the invention

In view of this, the object of the present invention is to provide a kind of double-two-order unit of negative feedback type hybrid integrator, be used for not increasing under the common mode feedback circuit situation, reduce the filter cell power consumption.

For realizing above-mentioned purpose, the invention provides a kind of double-two-order unit of negative feedback type hybrid integrator, comprising:

One first order mutual conductance-capacitance integrator comprises two PMOS transistors and an electric capacity, is used to receive input voltage signal and converts current signal to, to the electric capacity charging, forms first order integrator;

One second level comprises two PMOS transistors and an electric capacity based on the source follower integrator, is used for converting the voltage signal of said first order integrator output to current signal, to the electric capacity charging, forms second level integrator;

One feedback transistor comprises two nmos pass transistors, is used for the comprehensive plural limit of said two integrators, and control output common mode voltage;

One current source provides the branch current of said double-two-order unit.

The double-two-order unit of this negative feedback type hybrid integrator that embodiments of the invention provide; The feedback transistor and the second level form negative feedback loop based on the source follower in the source follower integrator, and the electric capacity in this integrator has been confirmed plural limit in the double-two-order unit transfer function.Therefore this unit can be used for cascade method design high-order analog filter; And the feedback transistor and the second level form negative feedback loop based on the source follower in the source follower integrator, stablize the dc point of fully differential structure output, therefore do not need common mode feedback circuit, have reduced the filter cell power consumption.Simultaneously, the input and output common mode electrical level of this double-two-order unit equates, compared with prior art, has increased the range of application of input and output common mode electrical levels.

In addition, double-two-order unit of the present invention can make the input direct-current working volts identical with the output direct-current working volts, is easy to adopt the cascaded design method to realize the high-order analog filter.In the transconductance value of the input transistors of the first order integrator transconductance value greater than feedback transistor, this double-two-order unit has the DC current gain greater than 0dB.

Description of drawings

Fig. 1 is the structural representation of single order mutual conductance-capacitance integrator in the prior art;

Fig. 2 be in the prior art single order based on the structural representation of source follower integrator;

Fig. 3 is the structural representation of a kind of embodiment of the double-two-order unit of negative feedback type hybrid integrator in the embodiments of the invention;

Fig. 4 is the sketch map that the double-two-order unit cascade realizes the quadravalence Butterworth filter in the embodiments of the invention;

The double-two-order unit cascade that Fig. 5 provides for the employing embodiment of the invention realizes the amplitude frequency curve sketch map of quadravalence Butterworth filter.

Embodiment

Embodiments of the invention provide a kind of double-two-order unit of negative feedback type hybrid integrator; The feedback transistor and the second level form negative feedback loop based on the source follower in the source follower integrator, and the electric capacity in this integrator has been confirmed plural limit in the double-two-order unit transfer function.Therefore this unit can be used for cascade method design high-order analog filter; And the feedback transistor and the second level form negative feedback loop based on the source follower in the source follower integrator, stablize the dc point of fully differential structure output, therefore do not need common mode feedback circuit, have reduced the filter cell power consumption.And double-two-order unit of the present invention can make the input direct-current working volts identical with the output direct-current working volts, is easy to adopt the cascaded design method to realize the high-order analog filter.In the transconductance value of the input transistors of the first order integrator transconductance value greater than feedback transistor, this double-two-order unit has the DC current gain greater than 0dB.

For making the object of the invention, technical scheme and advantage clearer, the present invention is made further detailed description below in conjunction with accompanying drawing.

Fig. 3 is the structure chart of the double-two-order unit of a kind of negative feedback type hybrid integrator of providing in the embodiment of the invention, and concrete circuit is described below:

One first order mutual conductance-capacitance integrator comprises two PMOS transistors and an electric capacity, is used to receive input voltage signal and converts current signal to, to the electric capacity charging, forms first order integrator;

One second level comprises two PMOS transistors and an electric capacity based on the source follower integrator, is used for converting the voltage signal of first order integrator output to current signal, to the electric capacity charging, forms second level integrator;

One feedback transistor comprises two nmos pass transistors, is used for two comprehensive plural limits of integrator, and control output common mode voltage;

One current source provides the branch current of double-two-order unit.

Wherein, said first order mutual conductance-capacitance integral implement body comprises:

The one PMOS manages (Mp3), is used to receive input voltage signal and converts current signal to, and the grid of this pipe connects first input end (Vip), and drain labeled is designated as net1, and source electrode links to each other with substrate, is labeled as net3;

The 2nd PMOS manages (Mp4), is used to receive input voltage signal and converts current signal to, and the grid of this pipe connects second input (Vin), and drain labeled is designated as net2, and source electrode and substrate meet net3;

First electric capacity (C1) is used to receive PMOS pipe (Mp3) and the 2nd PMOS manages the differential current signal that (Mp4) exports, a termination net1, another termination net2.

The said second level comprises based on the source follower integrator:

The 3rd PMOS manages (Mp1), is used to receive input voltage signal and converts current signal to, and the grid of this pipe meets net1, and grounded drain voltage GND, source electrode and substrate connect first output (Vop);

The 4th PMOS manages (Mp2), is used to receive input voltage signal and converts current signal to, and the grid of this pipe meets net2, and grounded drain voltage GND, source electrode and substrate connect second output (Von);

Second electric capacity (C2) is used to receive the 3rd PMOS pipe (Mp1) and the 4th PMOS manages the differential current signal that (Mp2) exports, a termination first output, another termination second output.

Said feedback transistor comprises:

The one NMOS manages (Mn1), is used for two comprehensive plural limits of integrator, and control output common mode voltage, the grid of this pipe connects first output, and drain electrode meets net1, source electrode and substrate earthed voltage GND;

The 2nd NMOS manages (Mn2), is used for two comprehensive plural limits of integrator, and control output common mode voltage, the grid of this pipe connects second output, and drain electrode meets net2, source electrode and substrate earthed voltage GND.

Said current source comprises:

First current source (Ib1) provides the branch current of double-two-order unit, positive termination supply voltage VDD, and negative terminal meets net3;

Second current source (Ib2) provides the branch current of double-two-order unit, positive termination supply voltage VDD, and negative terminal connects first output;

The 3rd current source (Ib2) provides the branch current of double-two-order unit, positive termination supply voltage VDD, and negative terminal connects second output.

In above double-two-order unit; The feedback transistor and the second level form negative feedback loop based on the source follower in the source follower integrator; Electric capacity in integrator has been confirmed plural limit in the double-two-order unit transfer function; Stablize the dc point of fully differential structure output, therefore do not need common mode feedback circuit; And can be easy to adopt the cascaded design method to realize the high-order analog filter so that the input direct-current working volts of this double-two-order unit are identical with the output direct-current working volts.

In addition, in the transconductance value of the input transistors of the first order integrator transconductance value greater than feedback transistor, this double-two-order unit has the DC current gain greater than 0dB; The value of differential capacitance element is C1/2 between the first order, and the value of differential capacitance element is C2/2 between the second level.

Embodiment for the double-two-order unit of further setting forth the negative feedback type hybrid integrator that the present invention proposes; As shown in Figure 3; The feedback transistor and the second level form negative feedback loop based on the source follower in the source follower integrator, and the electric capacity in integrator has been confirmed plural limit in the double-two-order unit transfer function.Ignore output mutual conductance, transistorized parasitic capacitance, and the mutual conductance of establishing Mp3 and Mp4 is gm1, the mutual conductance of establishing Mp1 and Mp2 is gm3, and the mutual conductance of establishing Mn1 and Mn1 is gm2.Can obtain filter transfer function:

$H\left(s\right)=\frac{\frac{{\mathrm{<figure-callout\; id="1"\; label="g\; m"\; filenames="H2008102271286E00041.png"\; state="\{\{state\}\}">g</figure-callout>}}_m{\mathrm{gg}}_{m2}}{C_{1}g{C}_2}}{{\mathrm{<figure-callout\; id="2"\; label="s"\; filenames="H2008102271286E00021.png,H2008102271286E00031.png"\; state="\{\{state\}\}">s</figure-callout>}}^2+\mathrm{sg}\frac{g_{m2}}{{\mathrm{<figure-callout\; id="2"\; label="C"\; filenames="H2008102271286E00021.png,H2008102271286E00031.png"\; state="\{\{state\}\}">C</figure-callout>}}_2}+\frac{{\mathrm{<figure-callout\; id="2"\; label="g\; m"\; filenames="H2008102271286E00021.png,H2008102271286E00031.png"\; state="\{\{state\}\}">g</figure-callout>}}_m{\mathrm{gg}}_{m3}}{C_{1}g{C}_2}}---\left(3\right)$

Can obtain filter characteristic parameter (ω ₀Be the pole characteristics frequency, Q is quality factor, and K is a DC current gain) be:

${\mathrm{\&omega;}}_0=2\mathrm{\&pi;}{\mathrm{<figure-callout\; id="0"\; label="f"\; filenames="H2008102271286E00041.png"\; state="\{\{state\}\}">f</figure-callout>}}_0=\sqrt{\frac{{\mathrm{<figure-callout\; id="2"\; label="g\; m"\; filenames="H2008102271286E00021.png,H2008102271286E00031.png"\; state="\{\{state\}\}">g</figure-callout>}}_m{\mathrm{gg}}_{m3}}{C_{1}g{C}_2}}---\left(4\right)$

$Q=\sqrt{\frac{C_2}{C_1}g\frac{g_{m3}}{g_{m2}}}---\left(5\right)$

$K=\frac{g_{m1}}{g_{m3}}---\left(6\right)$

Adopt the cascaded design method, the double-two-order unit cascade shown in Figure 3 with two the present invention propose realizes the quadravalence Butterworth filter, and is as shown in Figure 4.Adopt quadravalence Butterworth filter among SMIC (SemiconductorManufacturing International Corporation SMIC integrated circuit Manufacturing Co., Ltd) CMOS 0.18 μ m mixed signal process simulation Fig. 4, to verify correctness of the present invention.

The curve of describing among Fig. 5 is the amplitude frequency curve that adopts the double-two-order unit cascade realization quadravalence Butterworth filter of the present invention's proposition among Fig. 4, and the vertical coordinate axle of this curve chart and horizontal axis represent with decibel (dB) to be the amplitude characteristic and the correspondent frequency (Hz) of unit respectively.Know from this curve: (1), realized the transmission characteristic of formula (3); And then verified that the feedback transistor and the second level form negative feedback loop based on the source follower in the source follower integrator, the electric capacity in integrator has been confirmed plural limit in the double-two-order unit transfer function.(2), can point out that from formula (3) the quadravalence Butterworth filter of realizing among Fig. 5 has DC current gain 7.7dB, can set the g of each grade double-two-order unit _M1/ g _M3The DC current gain of the different adjustment of ratio whole filter.

Double-two-order unit provided by the invention adopts negative-feedback technology to combine to form double-two-order unit with mutual conductance-capacitance integrator with based on the source follower integrator, realizes the high-order analog filter to adopt the cascaded design method.Owing to adopt negative-feedback technology in this double-two-order unit; In conjunction with mutual conductance-capacitance integrator (shown in Figure 1) with based on two kinds of integrators of source follower integrator (shown in Figure 2); Therefore, this double-two-order unit is called as " double-two-order unit of negative feedback type hybrid integrator ".Because this unit adopts the stable output of negative feedback dc point, so this unit does not need common mode feedback circuit.

In a word, the above is merely preferred embodiment of the present invention, is not to be used to limit protection scope of the present invention.

Claims (4)

1. the double-two-order unit of a negative feedback type hybrid integrator is characterized in that, comprising:

One first order mutual conductance-capacitance integrator comprises two PMOS transistors and an electric capacity, is used to receive input voltage signal and converts current signal to, to the electric capacity charging, forms first order integrator;

One second level comprises two PMOS transistors and an electric capacity based on the source follower integrator, is used for converting the voltage signal of said first order integrator output to current signal, to the electric capacity charging, forms second level integrator;

One feedback transistor comprises two nmos pass transistors, is used for the comprehensive plural limit of said two integrators, and control output common mode voltage;

One current source provides the branch current of said double-two-order unit;

Said first order mutual conductance-capacitance integral implement body comprises:

The one PMOS pipe, the grid of this pipe connects first input end, and drain labeled is designated as net1, and source electrode links to each other with substrate, is labeled as net3;

The 2nd PMOS pipe, the grid of this pipe connects second input, and drain labeled is designated as net2, and source electrode and substrate meet net3;

First electric capacity, a termination net1, another termination net2;

The said second level specifically comprises based on the source follower integrator:

The 3rd PMOS pipe, the grid of this pipe meets net1, grounded drain voltage, source electrode and substrate connect first output;

The 4th PMOS pipe, the grid of this pipe meets net2, grounded drain voltage, source electrode and substrate connect second output;

Second electric capacity, a termination first output, another termination second output;

Said feedback transistor specifically comprises:

The one NMOS pipe, the grid of this pipe connects first output, and drain electrode meets net1, source electrode and substrate earthed voltage;

The 2nd NMOS pipe, the grid of this pipe connects second output, and drain electrode meets net2, source electrode and substrate earthed voltage;

Said current source comprises:

First current source, positive termination supply voltage, negative terminal meets net3;

Second current source, positive termination supply voltage, negative terminal connects first output;

The 3rd current source, positive termination supply voltage, negative terminal connects second output.

2. double-two-order unit according to claim 1; It is characterized in that; The said feedback transistor and the second level form negative feedback loop based on the source follower in the source follower integrator, confirm plural limit in the double-two-order unit transfer function with the said second level based on the electric capacity in the source follower integrator.

3. double-two-order unit according to claim 1 is characterized in that, the input direct-current working volts of said double-two-order unit are identical with the output direct-current working volts.

4. double-two-order unit according to claim 1 is characterized in that, in the transconductance value of the input transistors of the said first order mutual conductance-capacitance integrator transconductance value greater than said feedback transistor, this double-two-order unit has the DC current gain greater than 0dB.

Images