Amplifier with feedback
View Patent ↗A circuit includes a first resistive element coupled to a diode, a second resistive element, a first transistor having a first current electrode coupled the second resistive element, a second transistor having a first current electrode coupled to the first resistive element and a second current electrode coupled to the control electrode of the first transistor, a third resistive element coupled to a node, a third transistor having a first current electrode coupled to the node and having a control electrode and a second current electrode each coupled to the control electrode of the second transistor, a fourth transistor having a first current electrode coupled to the second resistive element and a control electrode coupled to the control electrode of the second transistor, and a fifth transistor having a first current electrode coupled to the node and a control electrode coupled to the second current electrode of the fourth transistor.
1. A circuit comprising:
a first resistive element having a first terminal coupled to a cathode of a diode and having a second terminal, wherein the diode provides an input to the circuit;
a second resistive element having a first terminal coupled to a first power supply terminal and having a second terminal;
a first transistor having a first current electrode coupled to the second terminal of the second resistive element, a control electrode, and a second control electrode coupled to provide an output of the circuit;
a second transistor having a first current electrode coupled to the second terminal of the first resistive element, a control electrode, and a second current electrode coupled to the control electrode of the first transistor;
a third resistive element having a first terminal coupled to the first power supply terminal and a second terminal coupled to a first circuit node;
a third transistor having a first current electrode coupled to the first circuit node, a control electrode coupled to the control electrode of the second transistor, and a second current electrode coupled to the control electrode of the second transistor;
a fourth transistor having a first current electrode coupled to the second terminal of the second resistive element, a control electrode coupled to the control electrode of the second transistor, and a second current electrode; and
a fifth transistor having a first current electrode coupled to the first circuit node, a second current electrode, and a control electrode coupled to the second current electrode of the fourth transistor.
2. The circuit of claim 1 , further comprising:
a first current source having a first terminal coupled to the second current electrode of the second transistor and a second current electrode coupled to a second circuit node;
a second current source having a first terminal coupled to the second current electrode of the third transistor and a second current electrode coupled to the second circuit node; and
a third current source having a first terminal coupled to the second current electrode of the fourth transistor and a second current electrode coupled to the second circuit node.
3. The circuit of claim 2 , further comprising:
a sixth transistor having a first current electrode coupled to the second terminal of the first transistor, a control electrode coupled to the second circuit node, and a second current electrode which provides the output of the circuit.
4. The circuit of claim 2 , further comprising:
a voltage reference having a first terminal coupled to the first power supply terminal and a second terminal coupled to the second circuit node.
5. The circuit of claim 4 , wherein the voltage reference comprises a zener diode having a cathode coupled to the first power supply terminal and an anode coupled to the second circuit node.
6. The circuit of claim 1 , wherein each of the second, third, and fourth transistors are further characterized as bipolar transistors.
7. The circuit of claim 6 , wherein a voltage at the first circuit node is at a base-to-emitter voltage of the third transistor above a base voltage of the fourth transistor.
8. The circuit of claim 1 , wherein a ratio of the output of the circuit to the input to the circuit varies proportionally with temperature of the diode.
9. The circuit of claim 1 , further comprising:
a reference voltage having a first terminal coupled to the first power supply terminal and having a second terminal; and
a sixth transistor having a first current electrode coupled to the second current electrode of the first transistor, a control electrode coupled to the second terminal of the reference voltage, and a second current electrode which provides the output of the circuit.
10. The circuit of claim 9 , further comprising:
a fourth resistive element having a first terminal coupled to the second terminal of the sixth transistor and a second terminal coupled to a second power supply terminal.
11. A circuit comprising:
a first resistive element having a first terminal coupled to a cathode of a diode and having a second terminal, wherein the diode provides an input to the circuit;
a second resistive element having a first terminal coupled to a first power supply terminal (Vbat) and having a second terminal;
a first transistor having a first current electrode coupled to the second terminal of the second resistive element, a control electrode, and a second current electrode coupled to provide an output of the circuit; and
an amplifier having a first input coupled to the second terminal of the second resistive element, a second input coupled to the second terminal of the first resistive element, and an output coupled to the control electrode of the first transistor, wherein the amplifier comprises:
a second transistor having a first current electrode coupled to the second terminal of the first resistive element a control electrode, and a second current electrode coupled to the control electrode of the first transistor wherein a first transistor voltage is defined as a voltage from the control electrode of the second transistor to the first current electrode of the second transistor;
a third transistor having a first current electrode coupled to the second terminal of the second resistive element, a control electrode coupled to the control electrode of the second transistor, and a second current electrode; and
a fourth transistor having a first current electrode, a control electrode coupled to the second current electrode of the third transistor, and a second current electrode, wherein a voltage at the first current electrode of the fourth transistor is greater than a voltage at the control electrode of the third transistor by an amount equal to the first transistor voltage.
12. The circuit of claim 11 , further comprising:
a third resistive element having a first terminal coupled to the first power supply terminal and a second terminal coupled to the first current electrode of the fourth transistor; and
a fifth transistor having a first current electrode coupled to the first current electrode of the fourth transistor, a control electrode coupled to the control electrode of the second transistor, and a second current electrode coupled to the control electrode of the second transistor.
13. The circuit of claim 12 , further comprising:
a first current source having a first terminal coupled to the second current electrode of the second transistor and a second current electrode coupled to a circuit node;
a second current source having a first terminal coupled to the second current electrode of the third transistor and a second current electrode coupled to the circuit node; and
a third current source having a first terminal coupled to the second current electrode of the fourth transistor and a second current electrode coupled to the circuit node.
14. The circuit of claim 13 , wherein each of the second, third, and fifth transistors are further characterized as bipolar transistors.
15. The circuit of claim 11 , further comprising:
a voltage reference having a first terminal coupled to the first power supply terminal and a second terminal coupled to a circuit node.
16. The circuit of claim 15 , further comprising:
a fifth transistor having a first current electrode coupled to the second terminal of the first transistor, a control electrode coupled to the circuit node, and a second current electrode which provides the output of the circuit.
17. The circuit of claim 16 , wherein the voltage reference comprises a zener diode having a cathode coupled to the first power supply terminal and an anode coupled to the circuit node.
18. The circuit of claim 11 , wherein a ratio of the output of the circuit to the input to the circuit varies proportionally with temperature of the diode.
19. A circuit comprising:
a first resistive element having a first terminal coupled to a cathode of a diode and having a second terminal, wherein the diode provides an input to the circuit;
a second resistive element having a first terminal coupled to a first power supply terminal and having a second terminal;
a first transistor having a first current electrode coupled to the second terminal of the second resistive element, a control electrode, and a second control electrode;
a zener diode having a cathode coupled to the first power supply terminal and an anode coupled to a first circuit node;
a sixth transistor having a first current electrode coupled to the second terminal of the first transistor, a control electrode coupled to the first circuit node, and a second current electrode which provides an output of the circuit; and
an amplifier having a first input coupled to the second terminal of the second resistive element, a second input coupled to the second terminal of the first resistive element, and an output coupled to the control electrode of the first transistor, wherein the amplifier comprises:
a second transistor having a first current electrode coupled to the second terminal of the second resistive element, a control electrode, and a second current electrode coupled to the control electrode of the first transistor;
a third resistive element having a first terminal coupled to the first power supply terminal and a second terminal coupled to a second circuit node;
a third transistor having a first current electrode coupled to the second circuit node, a control electrode coupled to the control electrode of the second transistor, and a second current electrode coupled to the control electrode of the second transistor;
a fourth transistor having a first current electrode coupled to the second terminal of the second resistive element, a control electrode coupled to the control electrode of the second transistor, and a second current electrode;
a fifth transistor having a first current electrode coupled to the second circuit node, a second current electrode, and a control electrode coupled to the second current electrode of the fourth transistor;
a first current source having a first terminal coupled to the second current electrode of the second transistor and a second current electrode coupled to the first circuit node;
a second current source having a first terminal coupled to the second current electrode of the third transistor and a second current electrode coupled to the first circuit node; and
a third current source having a first terminal coupled to the second current electrode of the fourth transistor and a second current electrode coupled to the first circuit node.
20. The circuit of claim 19 , wherein a ratio of the output of the circuit to the input to the circuit varies proportionally with temperature of the diode.