Low power reference current generator with tunable temperature sensitivity
An improved reference current generator is provided. A voltage difference generator generates two voltages that are separated by a relatively small electrical potential. The two closely separated voltages are applied across a resistive element with relatively large impedance value resulting in a small and stable reference current. The result is a power efficient, temperature compensated reference current generator.
1. A circuit for generating a reference current, said circuit comprising:
a voltage difference generator configured to receive an input voltage and operable to supply a first voltage and a second voltage with a difference between them and derived from the input voltage, where the first voltage and the second voltage have predefined values that are substantially insensitive to changes in the input voltage, said voltage difference generator comprising:
a reference voltage generator adapted to supply a first supply voltage;
a voltage buffer amplifier electrically coupled to said first supply voltage and adapted to provide a second supply voltage; and
a voltage ladder electrically coupled to said second supply voltage and adapted to supply said first voltage and said second voltage;
a first buffer electrically coupled to said first voltage, said first buffer being adapted to supply a third voltage, said first buffer comprising:
a first amplifier adapted to:
receive said first voltage;
receive said third voltage; and
compare said first voltage to said third voltage, and, in response, to output a first control voltage; and
a first transistor device adapted to receive said first control voltage, and, in response, to supply said third voltage;
a second buffer electrically coupled to said second voltage, said second buffer being adapted to supply a fourth voltage, said second buffer comprising:
a second amplifier adapted to:
receive said second voltage;
receive said fourth voltage; and
compare said second voltage to said fourth voltage, and, in response, to output a second control voltage; and
a second transistor device adapted to receive said second control voltage, and, in response, to supply said fourth voltage; and
a resistive element having a substantially linear operating behavior and electrically coupled between said third voltage and said fourth voltage, said resistive element being adapted to generate a reference current that is a function of said third voltage and said fourth voltage; and
a current mirror electrically connected in series with the resistive element, said current mirror being adapted to mirror the reference current, wherein the first buffer, the second buffer and the current mirror are comprised of transistors operating solely in a sub-threshold region.
2. The circuit of claim 1 wherein said first voltage and said second voltage are further characterized as being closely separated.
3. The circuit of claim 1 wherein said reference voltage generator is further characterized as comprising a plurality of transistor devices operating in a sub-threshold region.
4. The circuit of claim 3 wherein said plurality of transistor devices is further characterized as a plurality of a selected one of NMOS transistor devices or PMOS transistor devices.
5. The circuit of claim 1 wherein said voltage buffer amplifier is further characterized as comprising a plurality of transistor devices operating in a sub-threshold region.
6. The circuit of claim 1 wherein said voltage ladder is further characterized as comprising a plurality of series connected resistive circuit elements operating in a sub-threshold region.
7. The circuit of claim 6 wherein said plurality of series-connected resistive circuit elements is further characterized as a selected one of diode-connected NMOS devices or diode-connected PMOS devices.
8. The circuit of claim 1 wherein said resistive element is further characterized as a plurality of transistors operating in a sub-threshold region.
9. The circuit of claim 8 wherein said plurality of transistors is further characterized as comprising a selected one of NMOS or PMOS devices.
10. The circuit of claim 1 wherein at least a selected one of said voltage difference generator, said first buffer, said second buffer, and said resistive element are tuned to achieve at least a selected one of minimum temperature sensitivity, proportional-to-absolute temperature characteristic, and complementary-to-absolute temperature characteristic.
11. A circuit for generating a reference current, said circuit comprising:
a voltage difference generator configured to receive a single input voltage and operable to supply a first voltage and a second voltage with a difference between them and derived from the input voltage, where the first voltage and the second voltage have predefined values that are substantially insensitive to changes in the input voltage;
a first analog voltage buffer electrically coupled to said first voltage and operating at a first gain value to supply a third voltage, where the third voltage is derived as a function of the first voltage and the first gain value;
a second analog voltage buffer electrically coupled to said second voltage and operating at a second gain value to supply a fourth voltage, where the fourth voltage is derived as a function of the second voltage and the second gain value;
a resistive element having a substantially linear operating behavior and electrically coupled between said third voltage and said fourth voltage, said resistive element being adapted to generate a reference current that is a function of said third voltage and said fourth voltage; and
a current mirror electrically connected in series with the resistive element, said current mirror being adapted to mirror the reference current, wherein the first analog voltage buffer, the second analog voltage buffer and the current mirror are comprised of transistors operating solely in a sub-threshold region.
12. The circuit of claim 11 wherein said voltage difference generator is further characterized as comprising:
a reference voltage generator adapted to supply a first supply voltage;
a voltage buffer amplifier electrically coupled to said first supply voltage and adapted to provide a second supply voltage; and
a voltage ladder electrically coupled to said second supply voltage and adapted to supply said first voltage and said second voltage.
13. The circuit of claim 12 wherein said first buffer is further characterized as comprising:
a first amplifier adapted to:
receive said first voltage;
receive said third voltage; and
compare said first voltage to said third voltage, and, in response, to output a first control voltage; and
an NMOS device adapted to receive said first control voltage, and, in response, to supply said third voltage.
14. The circuit of claim 13 wherein said second buffer is further characterized as comprising:
a second amplifier adapted to:
receive said second voltage;
receive said fourth voltage; and
compare said second voltage to said fourth voltage, and, in response, to output a second control voltage; and
a PMOS device adapted to receive said second control voltage, and, in response, to supply said fourth voltage.
15. The circuit of claim 14 wherein said second amplifier is further characterized as comprising a plurality of transistor devices operating in a sub-threshold region.
16. The circuit of claim 14 wherein said second transistor device is further characterized as operating in a sub-threshold region.
17. The circuit of claim 13 wherein said first amplifier is further characterized as comprising a plurality of transistor devices operating in a sub-threshold region.
18. The circuit of claim 13 wherein said first transistor device is further characterized as operating in a sub-threshold region.
19. The circuit of claim 12 wherein said reference voltage generator is further characterized as comprising a plurality of transistor devices operating in a sub-threshold region.
20. The circuit of claim 19 wherein said plurality of transistor devices is further characterized as a plurality of a selected one of NMOS transistor devices or PMOS transistor devices.
21. The circuit of claim 12 wherein said voltage buffer amplifier is further characterized as comprising a plurality of transistor devices operating in a sub-threshold region.
22. The circuit of claim 12 wherein said voltage ladder is further characterized as comprising a plurality of series-connected resistive circuit elements operating in a sub-threshold region.
23. The circuit of claim 22 wherein said plurality of series-connected resistive circuit elements is further characterized as a selected one of diode-connected NMOS devices or diode connected PMOS devices.
24. The circuit of claim 11 wherein said first voltage and said second voltage are further characterized as being closely separated.
25. The circuit of claim 11 wherein said resistive element is further characterized as a plurality of transistors operating in a sub-threshold region.
26. The circuit of claim 25 wherein said plurality of transistors is further characterized as comprising a selected one of NMOS or PMOS devices.
27. The circuit of claim 11 wherein at least a selected one of said voltage difference generator, said first buffer, said second buffer, and said resistive element are tuned to achieve at least a selected one of minimum temperature sensitivity, proportional-to-absolute temperature characteristic, and complementary-to-absolute temperature characteristic.
28. A circuit for generating a reference current, said circuit comprising:
a voltage difference generator configured to receive a single input voltage and operable to supply a first voltage and a second voltage with a difference between them and derived from the input voltage, where the first voltage and the second voltage have predefined values that are substantially insensitive to changes in the input voltage;
a first analog voltage buffer electrically coupled to said first voltage and operating at a first gain value to supply a third voltage, where the third voltage is derived as a function of the first voltage and the first gain value;
a second analog voltage buffer electrically coupled to said second voltage and operating at a second gain value to supply a fourth voltage, where the fourth voltage is derived as a function of the second voltage and the second gain value;
a resistive element having a substantially linear operating behavior and electrically coupled between said third voltage and said fourth voltage, said resistive element being adapted to generate a reference current that is a function of said third voltage and said fourth voltage; and
a current mirror electrically coupled in series with the resistive element, said current mirror being adapted to mirror the reference current, wherein the voltage difference generator, the first analog voltage buffer and the second analog voltage buffer are comprised of transistors operating solely in a sub-threshold region.