Miscellaneous active electrical nonlinear devices – circuits – and – Specific identifiable device – circuit – or system – Nonlinear amplifying circuit
Reexamination Certificate
2002-12-20
2004-11-16
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific identifiable device, circuit, or system
Nonlinear amplifying circuit
C330S258000
Reexamination Certificate
active
06819170
ABSTRACT:
FIELD OF THE INVENTION
The present invention is generally related to circuits that sense differential signals with high common-mode voltage. More particularly, the present invention is related to an apparatus for sensing differential voltages with high common-mode levels such that noise, offset, and drift effects in the resulting circuit are minimized.
BACKGROUND OF THE INVENTION
A schematic diagram of a conventional dynamic bridge amplifier (
100
) is illustrated in FIG.
1
. The dynamic bridge amplifier includes five resistors (R
10
-R
14
) and an operational amplifier (A
1
).
Resistor R
1
is connected between V
1
and node N
1
. Resistor R
1
′ is connected between V
2
and node N
2
. Resistor R
2
is connected between node N
1
and GND. Resistor R
2
′ is connected between node N
2
and GND. Resistor R
3
is connected between node N
2
and VO. Operational amplifier A
1
includes a non-inverting input terminal that is connected to node N
1
, an inverting input terminal that is connected to node N
2
, and an output that is connected to VO.
In operation, an input signal is applied across the V
1
and V
2
terminals, and an output signal is provided at the VO terminal. The signal includes a common-mode portion (VCM) and a differential portion (VDIFF). The differential portion is a small signal, while the common-mode portion may be rather large. The signal levels are given by: V
1
=VCM−VDIFF/2 and V
2
=VCM+VDIFF/2.
R
1
is large compared to R
2
such that the common-mode voltages that are seen by the inputs of the operational amplifier (A
1
) are reduced. Amplifier A
1
drives a signal into the VO terminal until the voltage at node N
1
and N
2
are equal. The transfer function that is associated with circuit
100
can be described by the following equation: VO/VDIFF=−(1/2R
1
)*{R
3
[
1
+R
2
/R
2
′]+R
2
}. When resistors R
3
and R
2
have an equivalent parallel resistance as given by R
3
//R
2
′=R
2
, the transfer function may be simplified as: VO/VDIFF=−R
3
/R
1
.
SUMMARY OF THE INVENTION
Briefly stated, the present invention is related to a differential voltage amplifier that includes a dynamic level shifter circuit and an amplifier circuit. The dynamic level shifter circuit includes high-impedance current sources and resistors that move the common-mode levels of a differential input signal to a signal level that is suitable for the amplifier circuit. The amplifier circuit may be single-ended or differential. The dynamic level shifter circuit may include one or more additional current sources that are arranged to provide improved performance for low common-mode levels. A dynamic biasing scheme may be employed to improve operation over varied common-mode ranges. A trimming circuit may be used to adjust offsets in the system. A DC chop arrangement may be employed to remove offsets in the system.
A more complete appreciation of the present invention and its improvements can be obtained by reference to the accompanying drawings, which are briefly summarized below, the following detail description of presently preferred embodiments of the invention, and the appended claims.
REFERENCES:
patent: 5499526 (1996-03-01), Muro
patent: 5631602 (1997-05-01), Kearney et al.
patent: 6198350 (2001-03-01), Zarabadi
patent: 6380807 (2002-04-01), Brokaw
patent: 6727757 (2004-04-01), Venkatraman et al.
“High Common-Mode Voltage, Single-Supply Difference Amplifier AD8200,”Analog Devices, Inc., 2002, pp. 1-8.
Callahan Timothy P.
Cox Cassandra
Hertzberg Brett A.
Merchant & Gould
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