Variable gain amplifier with temperature compensation and gain linearity enhancement

1. A variable gain amplifier comprising:

a plurality of differential transistor pairs coupled in parallel, wherein

each transistor pair is coupled to a temperature dependent current source,

control inputs of the transistor pairs are coupled to a temperature dependent gain control signal, and

a temperature compensation circuit configured to generate the temperature dependent gain control signal, the temperature compensation circuit comprising:

a first transistor having a control terminal coupled to a control current source and to a zero temperature coefficient source and an output terminal coupled to current source proportional to temperature; and

a second transistor having an output terminal coupled to the current source proportional to temperature;

wherein the conduction current of the second transistor is applied as the temperature dependent gain control signal.

2. A variable gain amplifier as recited in claim 1 , further comprising emitter follower circuits coupled, respectively, to control terminals of the first and second transistors.

3. A variable gain amplifier as recited in claim 2 , further comprising cross-coupled transistors coupled between the emitter follower circuits and the control terminals of the first and second transistors.

4. A variable gain amplifier as recited in claim 2 , further comprising a voltage offset circuit coupled between the cross-coupled transistors and a control terminal of the second transistor.

5. A variable gain amplifier as recited in claim 1 , wherein:

control inputs of first transistors of the transistor pairs are coupled to each other in series through respective impedances and to the temperature dependent gain control signal; and

control inputs of second transistors of the transistor pairs are coupled to each other in series through respective impedances and to the temperature dependent gain control signal.

6. A method of controlling a variable gain amplifier composed of a plurality of parallel coupled differential transistor pairs, the method comprising:

producing a temperature dependent current source in the current path of each differential transistor pair;

generating a gain control current corresponding to a desired gain;

converting the generated control current to a temperature dependent gain control current and

applying the temperature dependent gain control current source in circuit with control inputs of the transistors of the paired differential transistors; and

modifying the temperature dependent gain control current source to compensate for gain non-linearity.

7. A method as recited in claim 6 , wherein the step of modifying comprises introducing an offset as a function of the gain control current.

8. A method of controlling a variable gain amplifier composed of a plurality of parallel coupled differential transistor pairs, the method comprising:

producing a temperature dependent current source in the current path of each differential transistor pair;

generating a gain control current corresponding to a desired gain;

converting the generated control current to a temperature dependent gain control current source;

applying the temperature dependent gain control current source in circuit with control inputs of the transistors of the paired differential transistors;

wherein the step of converting comprises;

generating a temperature dependent current source; and

multiplying the control current by the temperature dependent current source.