Broadband dc amplifier technique with very low offset voltage

Claim 2

An amplifier circuit comprising: a low-offset-amplifier including a low-offset-amplifier input and a low-offset-amplifier output, said low-offset-amplifier including a plurality of field effect transistor devices biased in a sub-threshold region; a broadband-amplifier including a broadband-amplifier input coupled to said low-offset-amplifier input, and a broadband-amplifier output, said broadband amplifier being biased above a threshold region; and, means for coupling between said broadband amplifier output and said low-offset-amplifier output to minimize offset voltage of said amplifier circuit.

Claim 3

The amplifier of claim 1, wherein said broadband amplifier input and said low-offset-amplifier input are each differential inputs.

Claim 4

The amplifier of claim 1, wherein said broadband amplifier output and said low-offset-amplifier output are each differential outputs.

Claim 5

The amplifier of claim 3 further comprising means for summing said broadband amplifier output and said low-offset-amplifier output.

Claim 6

A circuit providing for an operational amplifier with low offset and broad bandwidth characteristics, including two input stages, comprising: a first input stage including a dc and low frequency field effect transistor amplifier with a first operational gain, biased in a sub-threshold region, and adapted to provide a low frequency amplifier output; a second input stage including a broadband field effect transistor amplifier with a second operational gain, biased in a linear region and saturation region above threshold, and adapted to provide a broadband amplifier output; means for coupling said low frequency amplifier output and said broadband amplifier output to produce a coupled output; and, means for summing said coupled output.

Claim 7

A circuit providing for an operational amplifier with low offset and broad bandwidth characteristics, including two input stages, comprising: a first input stage including a dc and low frequency field effect transistor amplifier with a first operational gain, biased in a sub-threshold region, and adapted to provide a low frequency amplifier output; a second input stage including a broadband field effect transistor amplifier with a second operational gain, biased in a linear region and saturation region above threshold, and adapted to provide a broadband amplifier output; means for coupling said low frequency amplifier output and said broadband amplifier output to produce a coupled output; and, means for summing said coupled output.

Claim 8

The circuit of claim 5 wherein said first and second input stages are comprised of differential inputs.

Claim 9

The circuit of claim 5 wherein said low frequency amplifier output and said broadband amplifier output are differential outputs.

Claim 10

The circuit of claim 5 wherein said first and second input stages are comprised of transistors with predetermined width/length ratios.

Claim 11

The circuit of claim 8 wherein said first and second operational gains are adjustable by adjusting said predetermined width/length ratios of said transistors.

Claim 12

A circuit providing for an operational amplifier with low offset and broad bandwidth characteristics, including two input stages, comprising: a first input stage including a dc and low frequency field effect transistor amplifier with a first operational gain, operable in a sub-threshold region, and adapted to provide a low frequency amplifier output; a second input stage including a broadband field effect transistor amplifier with a second operational gain, operable in a linear region and saturation region above threshold, and adapted to provide a broadband amplifier output; means for coupling said low frequency amplifier output and said broadband amplifier output to produce a coupled output, said means for coupling comprising capacitive coupling; and, means for summing said coupled output.

Claim 13

A circuit providing for an operational amplifier with low offset and broad bandwidth characteristics, including two input stages, comprising: a first input stage including a dc and low frequency field effect transistor amplifier with a first operational gain, operable in a sub-threshold region, and adapted to provide a low frequency amplifier output; a second input stage including a broadband field effect transistor amplifier with a second operational gain, operable in a linear region and saturation region above threshold, and adapted to provide a broadband amplifier output; means for coupling said low frequency amplifier output and said broadband amplifier output to produce a coupled output, said means for coupling comprising capacitive coupling; and, means for summing said coupled output.

Claim 14

The circuit of claim 10 wherein said capacitive coupling comprises a plurality of capacitors connecting said differential outputs of said broadband amplifier to said differential outputs of said low-frequency amplifier.

Claim 15

The circuit of claim 11 wherein said capacitor values are predetermined to adjust a cross-over frequency of said circuit in a range of approximately 15 kHz to 50 kHz.

Claim 16

An amplifier circuit comprising: a first amplifying means with a first power supply, a differential input comprising of a first and second transistor means, and a differential output comprising of a first and third output means, said first amplifying means adapted to operate at dc and low frequencies; a second amplifying means with a second power supply, a differential input comprising of a third and fourth transistor means, and a differential output comprising of a second and fourth output means, said second amplifying means operable at broadband frequencies, higher than said low frequencies; a first signal input connected to said first and third transistor means, and a second signal input connected to said second and fourth transistor means, such that said first and second signal inputs are differentially received by said transistor means; a first capacitive coupling means between said first and second differential outputs; a second capacitive coupling means between said third and fourth differential outputs; and, a combining means to differentially receive the differential outputs.

Claim 17

An amplifier circuit comprising: a first amplifying means with a first power supply, a differential input comprising of a first and second transistor means, and a differential output comprising of a first and third output means, said first amplifying means adapted to operate at dc and low frequencies; a second amplifying means with a second power supply, a differential input comprising of a third and fourth transistor means, and a differential output comprising of a second and fourth output means, said second amplifying means operable at broadband frequencies, higher than said low frequencies; a first signal input connected to said first and third transistor means, and a second signal input connected to said second and fourth transistor means, such that said first and second signal inputs are differentially received by said transistor means; a first capacitive coupling means between said first and second differential outputs; a second capacitive coupling means between said third and fourth differential outputs; and, a combining means to differentially receive the differential outputs.

Claim 18

The amplifier circuit of claim 13 further comprising: a first voltage reference source adjustable to maintain operation of said first amplifying means within a subthreshold region; a second voltage reference source adjustable to maintain operation of said second amplifying means above said sub-threshold region; and, a transistor means of said first amplifying means adapted to shift a common mode output of said first amplifying means to a value approximately midway between said first and second power supplies.

Claim 19

The amplifier circuit of claim 13, wherein said combining means further comprises a differential amplifier circuit.

Claim 20

An amplifier circuit comprising: a first amplifier with a first power supply, a differential input comprising of a first and second transistor, and a differential output comprising of a first and third output, said first amplifier operable at dc and low frequencies; a second amplifier with a second power supply, a differential input comprising of a third and fourth transistor, and a differential output comprising of a second and fourth output, said second amplifier operable at broadband frequencies, higher than said low frequencies; a first signal input terminal connected to said first and third transistors, and a second signal input terminal connected to said second and fourth transistors, such that said first and second signal inputs are differentially received by the differential input transistors; a first capacitor between said first and second differential outputs; a second capacitor between said third and fourth differential outputs; a differential amplifier to differentially receive said differential outputs; a first voltage reference source adjustable to maintain operation of said first amplifier at a sub-threshold level; a second voltage reference source adjustable to maintain operation of said second amplifier above said sub-threshold level; and, a transistor of said first amplifier for shifting a common mode output of said first amplifier to a value approximately midway between said first and second power supplies.

Claim 21

An amplifier circuit comprising: a first amplifier with a first power supply, a differential input comprising of a first and second transistor, and a differential output comprising of a first and third output, said first amplifier operable at dc and low frequencies; a second amplifier with a second power supply, a differential input comprising of a third and fourth transistor, and a differential output comprising of a second and fourth output, said second amplifier operable at broadband frequencies, higher than said low frequencies; a first signal input terminal connected to said first and third transistors, and a second signal input terminal connected to said second and fourth transistors, such that said first and second signal inputs are differentially received by the differential input transistors; a first capacitor between said first and second differential outputs; a second capacitor between said third and fourth differential outputs; a differential amplifier to differentially receive said differential outputs; a first voltage reference source adjustable to maintain operation of said first amplifier at a sub-threshold level; a second voltage reference source adjustable to maintain operation of said second amplifier above said sub-threshold level; and, a transistor of said first amplifier for shifting a common mode output of said first amplifier to a value approximately midway between said first and second power supplies.

Claim 22

An amplifier circuit comprising: a low-offset-amplifier including a low-offset-amplifier input and a low-offset-amplifier output, wherein said low-offset-amplifier includes a plurality of field effect transistor devices operable in a sub-threshold region; a broadband-amplifier including a broadband-amplifier input coupled to said low-offset-amplifier input, and a broadband-amplifier output; and, means for coupling between said broadband amplifier output and said low-offset-amplifier output to minimize offset voltage of said amplifier circuit, said means for coupling including capacitive coupling.

Claim 23

An amplifier circuit comprising: a low-offset-amplifier including a low-offset-amplifier input and a low-offset-amplifier output, wherein said low-offset-amplifier includes a plurality of field effect transistor devices operable in a sub-threshold region; a broadband-amplifier including a broadband-amplifier input coupled to said low-offset-amplifier input, and a broadband-amplifier output; and, means for coupling between said broadband amplifier output and said low-offset-amplifier output to minimize offset voltage of said amplifier circuit, said means for coupling including capacitive coupling.

Claim 24

A circuit providing for an operational amplifier with low offset and broad bandwidth characteristics, including two input stages, comprising: a first input stage including a dc and low frequency field effect transistor amplifier with a first operational gain, operable in a sub-threshold region, and adapted to provide a low frequency amplifier output, said first operational gain being adjustable by resistive means; a second input stage including a broadband field effect transistor amplifier with a second operational gain, operable in a linear region and saturation region above threshold, and adapted to provide a broadband amplifier output, said second operational gain being adjustable by resistive means; means for coupling said low frequency amplifier output and said broadband amplifier output to produce a coupled output; and, means for summing said coupled output.

Claim 25

A circuit providing for an operational amplifier with low offset and broad bandwidth characteristics, including two input stages, comprising: a first input stage including a dc and low frequency field effect transistor amplifier with a first operational gain, operable in a sub-threshold region, and adapted to provide a low frequency amplifier output, said first operational gain being adjustable by resistive means; a second input stage including a broadband field effect transistor amplifier with a second operational gain, operable in a linear region and saturation region above threshold, and adapted to provide a broadband amplifier output, said second operational gain being adjustable by resistive means; means for coupling said low frequency amplifier output and said broadband amplifier output to produce a coupled output; and, means for summing said coupled output.

Claim 26

A circuit providing for an operational amplifier with low offset and broad bandwidth characteristics, including two input stages, comprising: a first input stage including a dc and low frequency field effect transistor amplifier with a first operational gain, operable in a sub-threshold region, and adapted to provide a low frequency amplifier output, wherein operation in a sub-threshold region of the low frequency amplifier is adjustable by a first voltage reference signal; a second input stage including a broadband field effect transistor amplifier with a second operational gain, operable in a linear region and saturation region above threshold, and adapted to provide a broadband amplifier output; means for coupling said low frequency amplifier output and said broadband amplifier output to produce a coupled output; and, means for summing said coupled output.

Claim 27

A circuit providing for an operational amplifier with low offset and broad bandwidth characteristics, including two input stages, comprising: a first input stage including a dc and low frequency field effect transistor amplifier with a first operational gain, operable in a sub-threshold region, and adapted to provide a low frequency amplifier output, wherein operation in a sub-threshold region of the low frequency amplifier is adjustable by a first voltage reference signal; a second input stage including a broadband field effect transistor amplifier with a second operational gain, operable in a linear region and saturation region above threshold, and adapted to provide a broadband amplifier output; means for coupling said low frequency amplifier output and said broadband amplifier output to produce a coupled output; and, means for summing said coupled output.

Claim 28

A circuit providing for an operational amplifier with low offset and broad bandwidth characteristics, including two input stages, comprising: a first input stage including a dc and low frequency field effect transistor amplifier with a first operational gain, operable in a sub-threshold region, and adapted to provide a low frequency amplifier output; a second input stage including a broadband field effect transistor amplifier with a second operational gain, operable in a linear region and saturation region above threshold, and adapted to provide a broadband amplifier output, wherein operation above threshold of the broadband amplifier is adjustable by a second voltage reference signal; means for coupling said low frequency amplifier output and said broadband amplifier output to produce a coupled output; and, means for summing said coupled output.

Claim 29

A circuit providing for an operational amplifier with low offset and broad bandwidth characteristics, including two input stages, comprising: a first input stage including a dc and low frequency field effect transistor amplifier with a first operational gain, operable in a sub-threshold region, and adapted to provide a low frequency amplifier output; a second input stage including a broadband field effect transistor amplifier with a second operational gain, operable in a linear region and saturation region above threshold, and adapted to provide a broadband amplifier output, wherein operation above threshold of the broadband amplifier is adjustable by a second voltage reference signal; means for coupling said low frequency amplifier output and said broadband amplifier output to produce a coupled output; and, means for summing said coupled output.

Claim 30

A circuit providing for an operational amplifier with low offset and broad bandwidth characteristics, including two input stages, comprising: a first input stage including a dc and low frequency field effect transistor amplifier with a first operational gain, operable in a sub-threshold region, and adapted to provide a low frequency amplifier output; a second input stage including a broadband field effect transistor amplifier with a second operational gain, operable in a linear region and saturation region above threshold, and adapted to provide a broadband amplifier output; means for coupling said low frequency amplifier output and said broadband amplifier output to produce a coupled output; and, means for summing said coupled output, said summing means including a differential amplifier.

Claim 31

A circuit providing for an operational amplifier with low offset and broad bandwidth characteristics, including two input stages, comprising: a first input stage including a dc and low frequency field effect transistor amplifier with a first operational gain, operable in a sub-threshold region, and adapted to provide a low frequency amplifier output; a second input stage including a broadband field effect transistor amplifier with a second operational gain, operable in a linear region and saturation region above threshold, and adapted to provide a broadband amplifier output; means for coupling said low frequency amplifier output and said broadband amplifier output to produce a coupled output; and, means for summing said coupled output, said summing means including a differential amplifier.