Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Rectangular or pulse waveform width control
Reexamination Certificate
2000-04-21
2002-01-08
Cunningham, Terry D. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Rectangular or pulse waveform width control
C327S175000
Reexamination Certificate
active
06337591
ABSTRACT:
BACKGROUND OF THE INVENTION
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.
FIG. 1
shows a typical prior art differential amplifier circuit
2
. Circuit
2
includes a differential amplifier
4
biased by four matching resistors
6
,
8
,
10
, and
12
. The advantage of the prior art differential amplifier circuit, such as the circuit shown in
FIG. 1
, is that Vin can be amplified with a CMIV (common mode input voltage) from V
SS
=−1V to close to V
DD
.
The disadvantages of the circuit of
FIG. 1
include the following: (1) four matching resistors
6
,
8
,
10
, and
12
are required; (2) the four resistors occupy valuable space on the die; (3) the CMRR (common mode rejection ratio) depends on how closely the resistors are matched, which is typically not better than 1% in an IC implementation; (4) the offset also depends on how closely the resistors are matched; and (5) V
ref
, which needs to supply current in
10
and
12
, should have a low impedance output; in practice, V
ref
is implemented as a voltage reference and follower op-amp
14
, as shown in FIG.
2
.
FIG. 3
shows another prior art differential amplifier circuit
16
. Circuit
16
includes differential amplifier
18
, resistors
20
and
22
, and provided with a Vref
24
. The advantages of circuit
16
of
FIG. 3
are as follows: (1) only two resistors
20
and
22
need be matched, which is much easier and results in a CMMR of better than 0.5%; (2) the CMRR is improved with respect to circuit
2
of
FIG. 1
, and the offset is better, both due to the reduced number of resistors required (resulting in improved resistor matching); and (3) V
ref
is a high impedance load, and therefore be a simple resistor divider; since there is no need for the buffer of
FIG. 2
, the circuit occupies a small area. The disadvantage of circuit
16
of
FIG. 3
is that it can only have a CMIV of V
SS
, since V
in
is referenced to V
SS
.
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
FIG. 4
, this is typically accomplished by providing an NPN transistor
22
which has its collector tied to a V
B
supply. As described more fully below, by regulating the voltage of emitter resistor
24
of the NPN transistor and repositioning resistor
24
, a &Dgr;V
be
/R current reference can be implemented on the high-side. Very good tolerance (±10%) and power supply rejection ratio has been implemented using this approach.
SUMMARY OF THE INVENTION
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.
REFERENCES:
patent: 5442317 (1995-08-01), Stengel
patent: 5574344 (1996-11-01), Matsuoka et al.
patent: 5917369 (1999-06-01), Nguyen
patent: 5949282 (1999-09-01), Nguyen et al.
patent: 6072361 (2000-06-01), Myers et al.
patent: 6127885 (2000-10-01), Colangelo
patent: 6215435 (2001-04-01), Parry et al.
Cunningham Terry D.
International Rectifier Corporation
Ostrolenk Faber Gerb & Soffen, LLP
Tra Quaai
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