US RE40549 E1
A high voltage linear current sense integrated circuit includes a differential amplifier circuit that can amplify a differential signal in the hundreds of millivolts near the power supply. In addition, a constant current using opposing minus temperature coefficient MOSFETs is provided. Accordingly, an op-amp circuit is provided with an input offset voltage which is constant and insensitive to temperature changes. A circuit for generating a current reference on the high side of the current sense IC also is provided.
1. A current sense integrated circuit, comprising:
an amplifier circuit for receiving and amplifying a differential analog input signal at a first voltage level containing current sense information, wherein the amplifier circuit includes a circuit to minimize inherent offset voltage temperature offset drift, comprising a first pair of mirrored MOSFET's, such that the circuit has an offset voltage which is equal to the difference between the respective gate-to-source voltages of the MOSFET's and remains constant over temperature variations;
a pulse width modulator circuit for converting the differential analog input signal to a pulse width modulated signal at the first voltage level; and
a level shift circuit for converting the pulse width modulated signal from the first voltage level to a second voltage level; and
a recovery circuit for reconstructing the analog input signal at the second voltage level..
2. The current sense integrated circuit of
3. The current sense integrated circuit of
4. The current sense integrated circuit of
5. The current sense integrated circuit of
6. The current sense integrated circuit of
7. A current sense integrated circuit as claimed in
8. A current sense integrated circuit as claimed in
This application claims the benefit of U.S. Provisional Application Ser. No. 60/130,648 filed Apr. 23, 1999, U.S. Provisional Application Ser. No. 60/166,727 filed Nov. 22, 1999, and U.S. Provisional Application Ser. No. 60/166,728 filed Nov. 22, 1999.
1. Field of the Invention
The present invention relates to circuitry for a high voltage integrated circuit (IC), and, more specifically, to a differential amplifier circuit that can amplify a differential signal in the hundreds of millivolts near the high voltage power supply, minimize inherent temperature offset drift, and generate a high side current reference in a current sense IC.
2. Description of the Related Art
The circuitry of a high voltage current sense IC, such as the IR2171 current sense IC sold by International Rectifier Corporation of El Segundo, Calif. are disclosed in U.S. patent application Ser. No. 09/266,822 filed Mar. 12, 1999, the entire disclosure of which is incorporated herein by reference.
The IR2171 provides a circuit for transferring static or time variable analog information without electrical isolation from a first (source) reference potential to a second (destination) reference potential.
More specifically, the IR2171 circuit recovers an input signal at a first potential which is offset by a common mode displacement from a second potential. The circuit in its most basic form includes: (1) circuitry for converting the input signal at the first potential to a pulse width modulated signal; and (2) circuitry for level shifting the pulse width modulated signal from the first potential to the second potential. The IR2171 advantageously can be used in a motor controller for transferring information relating to current flow through a high side resistor from a high voltage potential to a lower level potential for conditioning and processing the information.
Desirable features for a high voltage current sense IC, such as the IR2171, include a differential amplifier that can amplify a differential signal in the hundreds of millivolts near the power supply, minimize inherent temperature offset drift, and generate a high side current reference.
The disadvantages of the circuit of
A further shortcoming of the prior art is that conventional op amps have an input offset voltage which is temperature sensitive. It would be desirable to provide an op amp circuit in which the input offset voltage is constant and independent of changes in temperature.
High voltage current sense ICs require a high side current reference. Referring to
The present invention advantageously provides a differential amplifier circuit for a current sense IC which overcomes the disadvantages of the prior art circuits discussed above and can amplify a differential signal in the hundreds of millivolts near the power supply. In addition, the circuit of the present invention generates a constant current using opposing minus temperature coefficient MOSFETs. Accordingly, the invention provides an op-amp circuit with an input offset voltage which is constant and insensitive to temperature changes. The invention also advantageously provides a circuit for generating a current reference on the high side of the current sense IC.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.
The amplified signal from Pamp 32 is converted from analog to pulse form using pulse-width modulation encoding. In a preferred embodiment of the invention, a sawtooth generator 36 outputs a high frequency (e.g., 40 kHz) waveform (the sawtooth generator may, if desired, be replaced with a triangle wave generator). The output of pulse width modulator PWM 38 is a pulse width modulated waveform, in which the width of the pulses represents the voltage VSP.
PWM 38 output is fed to pulse generator 40 which produces a rising edge triggered pulse and a failing edge triggered pulse. These pulses are transposed to a lower potential through MOSFETs 42 and 44, and low side conversion circuit 46. Recovery of the digital PWM data is performed at the lower reference potential.
In the circuit 70 of
Circuit to Minimize Temperature Offset Drift—POPAMP
If the gate-to-source voltages of MOSFETs 82 and 84 are constant over temperature, the offset voltage should be constant over temperature. Thus, the circuit forces a constant current using the opposing minus temperature coefficient MOSFETs.
The relationship is based on the following formula for ID (drift current) and is shown in the graph of FIG. 10:
A high side current reference is provided according to the present invention by regulating the emitter voltage of the NPN transistor and repositioning the resistor as discussed above in connection with the prior art circuit of
The following equations are applicable to the prior art circuit shown in FIG. 4:
The implementation of the present invention in the prior art circuit of
Matching transistors 120 and 122 form the ΔVbe/R. The area ratio is 9:1 and the current ratio, determined by MOSFETs 126 and 128, is 1:5 so that
MOSFETs 130,132,133, and 136 form the amplifier. The output of the amplifier Vout is the drains of MOSFETs 130 and 136. The configuration is such that ΔVbe/R is mirrored from the source of MOSFET 132 to analog ground.
Other devices in circuit 35 are provided for startup, stability and to increase power supply rejection ratio. Preferably, in order to approach an ideal result, certain groups of devices are matched: Transistors 120 and 122; MOSFETs 130 and 132; MOSFETs 126, 128, and 138; MOSFETs 134, 136, and 140. Accordingly, ΔVbe depends only on the above matching and temperature.
A plurality of current reference signals can be provided to various portions of the IC by way of block 150.
Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. Therefore, the present invention is limited not by the specific disclosure herein, but only by the appended claims.