Low-complexity active transconductance circuit

1. An active transconductance circuit, comprising:

an input that receives an input voltage signal for the active transconductance circuit;

an output;

a fixed voltage node;

a voltage-to-current converter having a first end directly connected to said input and a second end directly connected to said fixed voltage node;

a voltage control circuit having a first end directly connected to said fixed voltage node for maintaining said fixed voltage node at a generally fixed voltage wherein said voltage control circuit has a common mode reference voltage input that receives a common mode reference voltage; and

a current mirror circuit having a first end directly connected to a second end of said voltage control circuit and having a second end directly connected to said output.

2. The circuit of claim 1 , wherein said input is a differential input, and said output is a differential output.

3. The circuit of claim 1 , wherein said current mirror circuit includes a current source coupled to said fixed voltage node for providing a generally constant current, first and second transistors having respective gates connected together, and a level shifter connected to said current source and said gates of said first and second transistors.

4. The circuit of claim 3 , wherein said level shifter includes a plurality of transistors configured as a source follower.

5. The circuit of claim 1 , wherein said voltage-to-current converter is a resistance.

6. The circuit of claim 1 , wherein said voltage control circuit includes a compare circuit that compares a voltage associated with said fixed voltage node to a reference voltage, said compare circuit having an output for providing an output signal based on said comparison.

7. The circuit of claim 6 , wherein said current mirror circuit includes a current source coupled to said fixed voltage node for providing a generally constant current, and wherein said voltage control circuit includes a transistor having a gate connected to said output of said compare circuit, said transistor having a drain and a source connected in series between said current source and said fixed voltage node.

8. The circuit of claim 7 , wherein said voltage control circuit includes a further transistor having a drain and a source connected in series between said fixed voltage node and an input of said compare circuit.

9. The circuit of claim 6 , wherein said current mirror circuit includes a current source coupled to said fixed voltage node for providing a generally constant current, first and second transistors having respective gates connected together, and a level shifter connected to said current source and said gates of said first and second transistors.

10. The circuit of claim 6 , wherein said compare circuit includes an operational amplifier circuit having a first input for receiving said reference voltage, and having a second input coupled to said fixed voltage node.

11. The circuit of claim 6 , wherein said voltage control circuit includes a transistor having a drain and a source connected in series between said fixed voltage node and an input of said compare circuit.

12. The circuit of claim 6 , wherein said voltage control circuit includes a resistive voltage divider circuit connected to said fixed voltage node, and wherein said compare circuit has a first input for receiving said reference voltage and a second input connected to a tap within said resistive voltage divider circuit.

13. The circuit of claim 1 , wherein said voltage-to-current converter is a resistance, and wherein said transconductance circuit has a transconductance that is a function of said resistance and a current ratio between respective transistors of said current mirror circuit.

14. An active filter circuit, comprising:

an active circuit component;

a passive circuit connected to said active circuit component; and

an active transconductance circuit including an input, an output connected to one of said active circuit component and said passive circuit, a fixed voltage node, a voltage-to-current converter having a first end directly connected to said input and a second end directly connected to said fixed voltage node, a voltage control circuit directly connected to said fixed voltage node for maintaining said fixed voltage node at a generally fixed voltage responsive to a common mode reference voltage received at a common mode input, and a current mirror circuit directly connected to said fixed voltage node and said output.

15. The circuit of claim 14 , wherein said passive circuit includes a resistor and a capacitor.

16. The circuit of claim 15 , wherein said resistor and said capacitor are connected in parallel with one another and with said active circuit component.

17. The circuit of claim 14 , wherein said active circuit component includes an operational amplifier circuit.

18. A method of producing an active transconductance, comprising:

converting an input voltage signal into a current using a voltage-to-current converter that has a first end directly connected to the input voltage signal and that has a second end directly connected to a fixed voltage node;

providing said current to the fixed voltage node;

maintaining said fixed voltage node at a generally fixed voltage using a voltage control circuit having a first end that is directly connected to said fixed voltage node wherein said voltage control circuit has a common mode reference voltage input that receives a common mode reference voltage; and

mirroring current from said voltage control circuit to an output with a current mirror circuit having a first end directly connected to a second end of said voltage control circuit and having a second end directly connected to said output.

19. The method of claim 18 , wherein said maintaining step includes comparing a voltage associated with said node to a reference voltage.

20. The method of claim 19 , wherein said maintaining step includes adjusting the voltage at said node based on a result of said comparing step.