Logarithmic amplifier with gain control

Claim 2

A logarithmic amplifier comprising: (a) a first non-linear element having an input terminal for receiving an input signal current and an output terminal; (b) a first transistor having a first controlled terminal coupled to the output terminal of the first non-linear element, a second controlled terminal and a control terminal; (c) a second non-linear element having an input terminal coupled to the second controlled terminal of the first transistor and an output terminal; (d) a load element having a first terminal coupled to the output terminal of the second non-linear element and a second terminal coupled to a first source of supply voltage; (e) a feedback network having an input terminal coupled to the input terminal of the second non-linear element and an output terminal coupled to the control terminal of the first transistor; (f) means for amplifying having an input terminal coupled to the input terminal of the first non-linear element and an output terminal for providing a logarithmic output voltage and; (g) an attenuation network for attenuating the logarithmic output voltage and applying the attenuated output voltage to the control terminal of the first transistor.

Claim 3

A logarithmic amplifier as in claim 1 further comprising a source of standing current coupled to the input terminal of the first non-linear element.

Claim 4

A logarithmic amplifier as in claim 1 further comprising a first source of bias current coupled to the first controlled terminal of the first transistor and a second source of bias current having a magnitude equal to the magnitude of the first source of bias current but opposite in direction, the second source of bias current being coupled to the second controlled terminal of the first transistor.

Claim 5

A logarithmic amplifier as in claim 1 wherein the first and second non-linear elements each comprises a Schottky diode having an anode coupled to the input terminal and a cathode coupled to the output terminal.

Claim 6

A logarithmic amplifier as in claim 1 wherein the first transistor comprises a bipolar PNP transistor having an emitter coupled to the first controlled terminal, a base coupled to the control terminal, and a collector coupled to the second controlled terminal.

Claim 7

A logarithmic amplifier as in claim 1 wherein the feedback network comprises: (a) a second transistor having a base coupled to the input terminal of the second non-linear element, a collector coupled to the control terminal of the first transistor, and an emitter; and (b) a third transistor having a base coupled to a reference voltage generator, a collector coupled to a second source of supply voltage, and an emitter coupled to the emitter of the second transistor and to a source of emitter current.

Claim 8

A logarithmic amplifier as in claim 6 wherein the reference voltage generator comprises: (a) a bias element coupled between the second source of supply voltage and the base of the third transistor; and (b) a diode having an anode coupled to the base of the third transistor and a cathode coupled to the first source of supply voltage.

Claim 9

A logarithmic amplifier as in claim 6 wherein the feedback network further comprises a first emitter resistor coupled between the emitter of the second transistor and the source of emitter current and a second emitter resistor coupled between the emitter of the third transistor and the source of emitter current.

Claim 10

A logarithmic amplifier as in claim 1 wherein the means for amplifying comprises: (a) an operational amplifier having a positive input coupled to the second source of supply voltage, a negative input, and an output; (b) an input resistor coupled between the input terminal of the amplifying means and the negative input of the operational amplifier; and (c) a feedback resistor coupled between the output terminal of the amplifying means and the negative input of the operational amplifier.

Claim 11

An improved diode circuit having increased dynamic range and gain control for use in a logarithmic amplifier comprising: (a) a first non-linear element having an input terminal for receiving an input signal current and an output terminal, the first non-linear element having a parasitic resistance equal to R d1 ; (b) a first transistor having a first controlled terminal coupled to the output terminal of the first non-linear element, a second controlled terminal and a control terminal, the first transistor having a parasitic resistance equal to R T ; (c) a second non-linear element having an input terminal coupled to the second controlled terminal of the first transistor and an output terminal, the second non-linear element having a parasitic resistance equal to R d2 ; (d) a load element having a first terminal coupled to the output terminal of the second non-linear element and a second terminal coupled to a first source of supply voltage, the load element having a value of R C that compensates for the parasitic resistances R d1 , R T , and R d2 ; and (e) a feedback network having an input terminal coupled to the input terminal of the second non-linear element and an output terminal coupled to the control terminal of the first transistor.

Claim 12

An improved diode circuit having increased dynamic range and gain control for use in a logarithmic amplifier comprising: (a) a first non-linear element having an input terminal for receiving an input signal current and an output terminal, the first non-linear element having a parasitic resistance equal to R d1 ; (b) a first transistor having a first controlled terminal coupled to the output terminal of the first non-linear element, a second controlled terminal and a control terminal, the first transistor having a parasitic resistance equal to R T ; (c) a second non-linear element having an input terminal coupled to the second controlled terminal of the first transistor and an output terminal, the second non-linear element having a parasitic resistance equal to R d2 ; (d) a load element having a first terminal coupled to the output terminal of the second non-linear element and a second terminal coupled to a first source of supply voltage, the load element having a value of R C that compensates for the parasitic resistances R d1 , R T , and R d2 ; and (e) a feedback network having an input terminal coupled to the input terminal of the second non-linear element and an output terminal coupled to the control terminal of the first transistor.

Claim 13

The improved diode circuit as in claim 10 further comprising a source of standing current coupled to the input terminal of the first non-linear element.

Claim 14

The improved diode circuit as in claim 10 further comprising a source of bias current coupled to the first controlled terminal of the first transistor and a second source of bias current having a magnitude equal to the magnitude of the first source of bias current but opposite in direction, the second source of bias current being coupled to the second controlled terminal of the first transistor.

Claim 15

The improved diode circuit as in claim 10 wherein the first and second non-linear elements each comprise a Schottky diode having an anode coupled to the input terminal and a cathode coupled to the output terminal.

Claim 16

The improved diode circuit as in claim 10 wherein the first transistor comprises a bipolar PNP transistor having an emitter coupled to the first controlled terminal, a base coupled to the control terminal, and a collector coupled to the second controlled terminal.

Claim 17

The improved diode circuit as in claim 10 wherein the feedback network comprises: (a) a second transistor having a base coupled to the input terminal of the second non-linear element, a collector coupled to the control terminal of the first transistor, and an emitter; and (b) a third transistor having a base coupled to a reference voltage generator, a collector coupled to a second source of supply voltage, and an emitter coupled to the emitter of the second transistor and to a source of emitter current.

Claim 18

The improved diode circuit as in claim 15 wherein the reference voltage generator comprises: (a) a bias element coupled between the second source of voltage supply and the base of the third transistor; and (b) a diode having an anode coupled to the base of the third transistor and a cathode coupled to the first source of supply voltage.

Claim 19

The improved diode circuit as in claim 15 wherein the feedback network further comprises a first emitter resistor coupled between the emitter of the second transistor and the source of the emitter current and a second emitter resistor coupled between the emitter of the third resistor and the source of the emitter current.