Circuit for performing exponential temperature compensation in an oscillator

1 . An error compensation circuit for eliminating temperature-based frequency error in an oscillator, comprising:

a current limiting circuit comprising a first metal-oxide-semiconductor (MOS) device and a first resistive element connected to the first MOS device, the current limiting circuit configured to turn off the first MOS device to provide zero compensation current at a first temperature lower than a first reference value;

a current generation circuit comprising a second MOS device, which is a source follower MOS device, and a second resistive element, which is a degeneration resistor, connected in series with the second MOS device, the current generation circuit configured to generate a compensation current at a second temperature higher than a second reference value; and

a p-channel-metal-oxide-semiconductor (PMOS) current mirror configured to output the compensation current to a capacitor of the oscillator.

2 . The error compensation circuit as claimed in claim 1 , wherein the first MOS device comprises a first transistor, and the first resistive element comprises a first resistor and a second resistor.

3 . The error compensation circuit as claimed in claim 2 , wherein the current limiting circuit is configured to:

receive a highly proportional-to-absolute-temperature (PTAT) voltage at a gate of by the first transistor, and

wherein the first transistor remains turned off at temperatures below the first reference value, and acts as a resistor at temperatures higher than the second reference value.

4 . The error compensation circuit as claimed in claim 1 , wherein the current generation circuit comprises a second transistor, a third resistor, a fourth resistor and a diode, and

wherein the second resistive element is the third resistor and the second transistor is the second MOS device.

5 . The error compensation circuit as claimed in claim 4 , wherein a gate of the second transistor is configured to:

receive one of a slightly proportional-to-absolute-temperature (PTAT) voltage, and a complimentary to absolute temperature (CTAT) voltage, and

output a compensation current I comp based on the one of the PTAT voltage and the CTAT voltage.

6 . The error compensation circuit as claimed in claim 5 , wherein the compensation current is generated for compensating a comparator delay variation based on the following equation:

I

c

⁢

o

⁢

m

⁢

p

=

(

V

B

-

V

⁢

GS

M

⁢

2

)

/

R

1

,

wherein I comp is the compensation current, V B is one of the PTAT voltage and CTAT voltage, VGS M2 is a gate voltage of the second transistor, and R 1 is a resistance value of the third resistor.

7 . The error compensation circuit as claimed in claim 1 , wherein the current generation circuit is configured to generate an exponential current output with respect to range of temperatures higher than the second reference value based on the compensation current.

8 . The error compensation circuit as claimed in claim 1 , wherein a predetermined current is output to the capacitor of the oscillator at the second temperature.

9 . The error compensation circuit as claimed in claim 1 , wherein the first reference value and the second reference value are same.

10 . The error compensation circuit as claimed in claim 1 , wherein the first reference value and the second reference value are different.