Linear gain control amplifier

Claim 2

An amplification circuit for amplifying an input signal where signal gain in decibels (dB) is a linear function of a control signal comprising: compensation means for receiving a control signal and generating a corresponding compensation signal according to predetermined gain compensation characteristics; input amplification means for, receiving an input signal and said compensation signal, amplifying said input signal at an input gain level determined by said compensation signal and providing a corresponding input amplification means output signal, said input amplification means gain in dB being a linear function of said control signal over a predetermined gain range; filter means for receiving and filtering said input amplification means output signal; and output amplification means for, receiving said filtered input amplification means output signal and said compensation signal, amplifying said filtered input amplification means output signal at an output gain level determined by said compensation signal and providing a corresponding output amplification means output signal, said output amplification means gain in dB being a linear function of said control signal over said predetermined gain range.

Claim 3

The amplification circuit of claim 1 wherein: said filter means has a predetermined input and output impedance; said input amplification means is further for providing a selected output impedance so as to match said filter means input impedance; and said output amplification means is further for providing a selected input impedance so as to match said filter means output impedance.

Claim 4

The amplification circuit of claim 1 wherein said filter means comprises a surface acoustic wave (SAW) filter.

Claim 5

The amplification circuit of claim 3 wherein said input and output amplification means each comprises a FET amplifier.

Claim 6

The amplification circuit of claim 4 wherein: said filter has a predetermined input and output impedance; said input amplification means FET amplifier has a predetermined output impedance matched to said filter input impedance; and said output amplification means FET amplifier has a predetermined input impedance matched to said filter output impedance.

Claim 7

An amplifier circuit, for use with an automatic gain control (AGC) circuit which generates an AGC signal, for in response to said AGC signal providing gain control of an input signal over a high dynamic range, said gain control being a linear function of said AGC control signal comprising: a compensation circuit having an input and an output, said compensation circuit capable of receiving said AGC signal at said compensation circuit input and modifying said AGC signal according to predetermined gain compensation characteristics so as to provide a modified AGC signal at said compensation circuit output; a first amplifier having a pair of inputs and an output, one of said first amplifier inputs coupled to said compensation circuit output and another one of said first amplifier inputs capable of receiving said input signal, said first amplifier having portions of a gain range in decibels (dB) which are piecewise linear with respect to said AGC signal, and said first amplifier gain range linear with respect to said modified AGC signal; a filter having an input and an output, said filter input coupled to said first amplifier output; and a second amplifier having a pair of inputs and an output, one of said second amplifier inputs coupled to said compensation circuit output and another one of said second amplifier inputs coupled to said filter output, said second amplifier having portions of a gain range in dB which are piecewise linear with respect to said AGC signal, and said second amplifier gain range linear with respect to said modified AGC signal.

Claim 8

An amplifier circuit, for use with an automatic gain control (AGC) circuit which generates an AGC signal, for in response to said AGC signal providing gain control of an input signal over a high dynamic range, said gain control being a linear function of said AGC control signal comprising: a compensation circuit having an input and an output, said compensation circuit capable of receiving said AGC signal at said compensation circuit input and modifying said AGC signal according to predetermined gain compensation characteristics so as to provide a modified AGC signal at said compensation circuit output; a first amplifier having a pair of inputs and an output, one of said first amplifier inputs coupled to said compensation circuit output and another one of said first amplifier inputs capable of receiving said input signal, said first amplifier having portions of a gain range in decibels (dB) which are piecewise linear with respect to said AGC signal, and said first amplifier gain range linear with respect to said modified AGC signal; a filter having an input and an output, said filter input coupled to said first amplifier output; and a second amplifier having a pair of inputs and an output, one of said second amplifier inputs coupled to said compensation circuit output and another one of said second amplifier inputs coupled to said filter output, said second amplifier having portions of a gain range in dB which are piecewise linear with respect to said AGC signal, and said second amplifier gain range linear with respect to said modified AGC signal.

Claim 9

The circuit of claim 6 wherein said filter comprises a surface acoustic wave (SAW) bandpass filter.

Claim 10

The circuit of claim 6 wherein said first and second amplifiers each comprise a dual gate FET amplifier.

Claim 11

The circuit of claim 7 wherein said first and second amplifiers each comprise a dual gate FET amplifier.

Claim 12

The circuit of claim 9 wherein: said first amplifier further comprises a first impedance matching circuit coupled to said first amplifier output for matching an input impedance of said filter for a predetermined level of triple transit response of said filter; and said second amplifier further comprises a second impedance matching circuit coupled to said first amplifier other input for matching an output impedance of said filter for said predetermined level of triple transit response of said filter; and wherein said filter has an insertion loss corresponding to impedance levels established by said first amplifier in combination with said first impedance matching circuit and said second amplifier in combination with said second impedance matching circuit.

Claim 13

The circuit of claim 6 wherein said compensation circuit comprises: an operational amplifier having a noninverting input capable of receiving a reference voltage, an inverting input capable of receiving an AGC signal and an output; and a nonlinear feedback network coupled between said operational amplifier output and said inverting input.

Claim 14

The circuit of claim 11 further comprising thermal compensation means coupled to said noninverting input for controlling the level of said reference voltage as applied to said noninverting input.

Claim 15

The circuit of claim 9 wherein said compensation circuit comprises: an operational amp having a noninverting input capable of receiving a reference voltage, an inverting input capable of receiving an AGC signal and an output; and a nonlinear feedback network coupled between said op amp output and said inverting input.

Claim 16

The circuit of claim 13 further comprising compensation means coupled to said noninverting input for controlling the level of said reference voltage as applied to said noninverting input.

Claim 19

The method of claim 15, wherein said input signal is amplified by a first amplifier, said first amplified signal is filtered by a filter having a predetermined input and output impedance, and said filtered first amplified signal is amplified by a second amplifier, said method further comprising the step of providing impedance matching of said first and second amplifiers to said filter for a predetermined level of filter triple transit response.

Claim 20

The method of claim 15 wherein said step of generating said compensation signal comprises the steps of: modifying said control signal according to a first gain compensation curve when said control signal is below a first predetermined level; and modifying said control signal according to a second gain compensation curve when said control signal is above said first predetermined level.

Claim 21

The amplification circuit of claim 1 wherein said input and output amplification means each provide signal gain in dB as a first linear function of said control signal over a portion of said predetermined gain range and as a second linear function of said control signal over gains exceeding said predetermined gain range portion, said compensation means modifying said control signal corresponding to input and output amplification means gains exceeding said predetermined gain range.

Claim 22

The circuit of claim 6 wherein said first and second amplifiers are responsive to said modified AGC signal for providing a signal gain in dB over said gain range which is in linear correspondence with said AGC signal.