Controllable temperature coefficient bias circuit
A controllable temperature coefficient bias (CTCB) circuit is disclosed. The CTCB circuit can provide a bias to an amplifier. The CTCB circuit includes a variable with temperature (VWT) circuit having a reference circuit and a control circuit. The control circuit has a control output, a first current control element and a second current control element. Each current control element has a “controllable” resistance. One of the two current control elements may have a relatively high temperature coefficient and another a relatively low temperature coefficient. A controllable resistance of one of the current control elements increases when the controllable resistance of the other current control element decreases. However, the “total resistance” of the current control circuit remains constant with a constant temperature. The VWT circuit has an output with a temperature coefficient that is determined by the relative amount of current that flows through each current control element of the control circuit. A Current Digital to Analog Converter (IDAC) scales the output of the VWT and provides the scaled output to an amplifier bias input.
1. A controllable temperature coefficient bias circuit including:
(a) a constant current with temperature (CWT) circuit having an output;
(b) a first variable scaling circuit having a signal input coupled to the output of the CWT circuit and an output comprising a scaled version of the output of the CWT circuit;
(c) a Proportional To Ambient Temperature (PTAT) circuit having an output; and
(d) a second variable scaling circuit having a signal input coupled to the output of the PTAT circuit and an output comprising a scaled version of the output of the PTAT circuit and coupled to the output of the first variable scaling circuit.
2. The controllable temperature coefficient bias circuit of claim 1 , further including a control processor having a first and second control output and wherein:
(a) the first variable scaling circuit includes a control input coupled to the first control output of the control processor and is configured to output a current proportional to signals applied to the first variable scaling circuit signal input scaled in response to a first scaling factor received at the control input of the first variable scaling circuit; and
(b) the second variable scaling circuit includes a control input coupled to the second control output of the control processor and is configured to output a current proportional to signals applied to the second variable scaling circuit signal input scaled in response to a second scaling factor received at the control input of the second variable scaling circuit.
3. The controllable temperature coefficient bias circuit of claim 2 , wherein a temperature coefficient of the coupled outputs of the first variable scaling circuit and the second variable scaling circuit may be adjusted by adjusting the relative values of the first and second scaling factors.
4. The controllable temperature coefficient bias circuit of claim 2 , wherein:
(a) the first variable scaling circuit includes at least two selectively enabled current mirrors, the current in each enabled current mirror of the first variable scaling circuit being summed at the output of the first variable scaling circuit; and
(b) the second variable scaling circuit includes at least two selectively enabled current mirrors, the current in each enabled current mirror of the second variable scaling circuit being summed at the output of the second variable scaling circuit.
5. The controllable temperature coefficient bias circuit of claim 4 , wherein a temperature coefficient of the coupled output of the first variable scaling circuit and the second variable scaling circuit may be adjusted by adjusting the relative values of the first and second scaling factors.
6. The controllable temperature coefficient bias circuit of claim 1 , wherein the CWT circuit includes:
(a) a transistor having a gate, a drain coupled to a node, and a source, the source configured to be coupled to a voltage supply;
(b) a resistor coupled between the node and configured to be coupled to ground;
(c) a reference voltage source; and
(d) an operational amplifier having a first input coupled to the reference voltage source, a second input coupled to the node, and an output coupled to the gate to the transistor.
7. The controllable temperature coefficient bias circuit of claim 1 , further including a control processor having a first and second control output and wherein:
(a) the first variable scaling circuit includes a control input coupled to the first control output of the control processor and is configured to provide an output proportional to a first scaling factor received at the control input of the first variable scaling circuit; and
(b) the second variable scaling circuit includes a control input coupled to the second control output of the control processor and is configured to provide an output proportional to a second scaling factor received at the control input of the second variable scaling circuit.
8. The controllable temperature coefficient bias circuit of claim 7 , wherein a temperature coefficient of the coupled outputs of the first variable scaling circuit and the second variable scaling circuit may be adjusted by adjusting the relative values of the first and second scaling factors.
9. The controllable temperature coefficient bias circuit of claim 7 , wherein:
(a) the first variable scaling circuit includes at least two selectively enabled current mirrors, the current in each enabled current mirror of the first variable scaling circuit being summed at the output of the first variable scaling circuit; and
(b) the second variable scaling circuit includes at least two selectively enabled current mirrors, the current in each enabled current mirror of the second variable scaling circuit being summed at the output of the second variable scaling circuit.
10. The controllable temperature coefficient bias circuit of claim 9 , wherein a temperature coefficient of the coupled output of the first variable scaling circuit and the second variable scaling circuit may be adjusted by adjusting the relative values of the first and second scaling factors.
11. An amplifier circuit including:
(a) a constant current with temperature (CWT) circuit having an output;
(b) a first variable scaling circuit having a signal input coupled to the output of the CWT circuit and an output comprising a scaled version of the output of the CWT circuit;
(c) a Proportional To Ambient Temperature (PTAT) circuit having an output;
(d) a second variable scaling circuit having a signal input coupled to the output of the PTAT circuit and an output comprising a scaled version of the output of the PTAT circuit; and
(e) an amplifier including a bias input coupled to the output of the first variable scaling circuit and the second variable scaling circuit.
12. The amplifier circuit of claim 11 , wherein the first variable scaling circuit and the second variable scaling circuit enable trimming of a bias current or voltage applied to the bias input of the amplifier to offset changes of a transconductance value g m of the amplifier due to temperature changes affecting the amplifier circuit.
13. The amplifier circuit of claim 11 , further including a control processor having a first and second control output and wherein:
(a) the first variable scaling circuit includes a control input coupled to the first control output of the control processor and is configured to output a current proportional to signals applied to the first variable scaling circuit signal input scaled in response to a first scaling factor received at the control input of the first variable scaling circuit; and
(b) the second variable scaling circuit includes a control input coupled to the second control output of the control processor and is configured to output a current proportional to signals applied to the second variable scaling circuit signal input scaled in response to a second scaling factor received at the control input of the second variable scaling circuit.
14. The amplifier circuit of claim 13 , wherein a temperature coefficient of the coupled outputs of the first variable scaling circuit and the second variable scaling circuit may be adjusted by adjusting the relative values of the first and second scaling factors.
15. The amplifier circuit of claim 13 , wherein:
(a) the first variable scaling circuit includes at least two selectively enabled current mirrors, the current in each enabled current mirror of the first variable scaling circuit being summed at the output of the first variable scaling circuit; and
(b) the second variable scaling circuit includes at least two selectively enabled current mirrors, the current in each enabled current mirror of the second variable scaling circuit being summed at the output of the second variable scaling circuit.
16. The amplifier circuit of claim 15 , wherein a temperature coefficient of the coupled output of the first variable scaling circuit and the second variable scaling circuit may be adjusted by adjusting the relative values of the first and second scaling factors.
17. The amplifier circuit of claim 11 , wherein the CWT circuit includes:
(a) a transistor having a gate, a drain coupled to a node, and a source, the source configured to be coupled to a voltage supply;
(b) a resistor coupled between the node and configured to be coupled to ground;
(c) a reference voltage source; and
(d) an operational amplifier having a first input coupled to the reference voltage source, a second input coupled to the node, and an output coupled to the gate to the transistor.
18. The amplifier circuit of claim 11 , further including a control processor having a first and second control output and wherein:
(a) the first variable scaling circuit includes a control input coupled to the first control output of the control processor and is configured to provide an output proportional to a first scaling factor received at the control input of the first variable scaling circuit; and
(b) the second variable scaling circuit includes a control input coupled to the second control output of the control processor and is configured to provide an output proportional to a second scaling factor received at the control input of the second variable scaling circuit.
19. The amplifier circuit of claim 18 , wherein a temperature coefficient of the coupled outputs of the first variable scaling circuit and the second variable scaling circuit may be adjusted by adjusting the relative values of the first and second scaling factors.
20. The amplifier circuit of claim 18 , wherein:
(a) the first variable scaling circuit includes at least two selectively enabled current mirrors, the current in each enabled current mirror of the first variable scaling circuit being summed at the output of the first variable scaling circuit; and
(b) the second variable scaling circuit includes at least two selectively enabled current mirrors, the current in each enabled current mirror of the second variable scaling circuit being summed at the output of the second variable scaling circuit.