Voltage supply insensitive bias circuits
View Patent ↗A voltage-insensitive circuit includes a second circuit, and a biasing means for providing a constant bias current to the second circuit, the bias current being insensitive to power fluctuations of the voltage-insensitive circuit.
1. A voltage-insensitive bias circuit, comprising:
a first resistor connected between a power voltage node and a voltage divider node;
a second resistor connected between a ground node and the voltage divider node;
a first bipolar transistor having a first base, a first collector and a first emitter;
a fourth resistor connected between the first base and the voltage divider node;
a fifth resistor connected between the first collector and the power voltage node;
a sixth resistor connected between the first emitter and the ground node;
a second bipolar transistor having a second base, a second collector and a second emitter, wherein the second collector is connected to the power voltage node;
a seventh resistor connected between the first collector and the second base; and
a second diode having a second anode and a second cathode, and a third diode having a third anode and a third cathode, wherein the second anode is connected to the second base, the second cathode is connected to the third anode, and the third cathode is connected to the ground node;
wherein the second emitter provides a first bias output to a second circuit, the first bias output being appreciably insensitive to voltage fluctuations of the voltage power node.
2. The voltage-insensitive bias circuit of claim 1 , further comprising:
a thermal compensation circuit having a first end terminal and a second end terminal, the thermal compensation circuit including a first diode in series with a third resistor, wherein the first end terminal is connected to the voltage divider node, the second end terminal is connected to the ground node, and the first diode is arranged to be forward biased when a positive voltage is applied to the power voltage node.
3. The voltage-insensitive bias circuit of claim 2 , wherein the second resistor and the third resistor have a ratio of resistive values that substantially optimizes thermal stability of the bias circuit.
4. The voltage-insensitive bias circuit of claim 2 , wherein the voltage of the voltage divider node is determined by a first resistive value of the first resistor, a second resistive value of the second resistor, a third resistive value of the third resistor, a first base-emitter voltage of the first transistor and a first forward-bias voltage of the first diode.
5. The voltage-insensitive bias circuit of claim 4 , wherein a temperature variation causing an increase in the first base-emitter voltage is substantially compensated by an increase of the voltage of the voltage divider node caused by a temperature-related increase in the first forward-bias voltage.
6. The voltage-insensitive bias circuit of claim 1 , further comprising a bias modulation circuit having at least one transistor and a modulation control output, wherein the bias modulation circuit is adapted to adjust the first bias output.
7. The voltage-insensitive bias circuit of claim 6 , wherein the modulation control output is connected to the third anode.
8. The voltage-insensitive bias circuit of claim 6 , wherein the modulation control output is connected to the second base.
9. The voltage-insensitive bias circuit of claim 6 , wherein a first slope of the first bias output as a function of the voltage of the power-voltage node is a function of a fourth resistive value of the fourth transistor, a fifth resistive value of the fifth transistor and a sixth resistive value of the sixth transistor.
10. The voltage-insensitive bias circuit of claim 6 , wherein the fourth resistive value, the fifth resistive value and the sixth resistive value have values that cause the first slope to be substantially level for large voltage fluctuations of the power-voltage node.
11. The voltage-insensitive bias circuit of claim 1 , further comprising a bias modulation means coupled to at least one of the second transistor and the second diode for adjusting the first bias output.