Circuit and method for startup of a band-gap reference circuit

1. A method of starting up a band-gap reference circuit having a first comparator and a band-gap voltage output, comprising:

providing a startup reference signal by injecting a current from a current source into a p-type transistor, the p-type transistor providing the start-up reference signal;

comparing with a second comparator the band-gap voltage output to the startup reference signal; and

based on the comparing operation, selectively activating a startup current for starting up the band-gap reference circuit, the startup current raising the band-gap voltage output of the band-gap reference circuit.

2. The method of claim 1 , wherein the voltage across the transistor is between a base and an emitter of the transistor.

3. The method of claim 1 , wherein the comparing operation utilizes a comparator with hysteresis.

4. The method of claim 1 , wherein the operation of selectively activating the startup current further comprises:

enabling the startup current if the band-gap voltage output is less than the startup reference signal.

5. The method of claim 4 , wherein the enabling operation pulls the band-gap voltage output towards a desired convergence point.

6. The method of claim 4 , wherein the enabling operation sinks the startup current.

7. The method of claim 1 , wherein the operation of selectively activating a startup current further comprises:

disabling the startup current if the band-gap voltage output is greater than the startup reference signal.

8. A band-gap reference circuit, comprising:

a circuit portion for generating a band-gap voltage output of the band-gap reference circuit, the circuit portion including a first comparator;

a circuit portion providing a startup reference voltage, wherein the circuit portion providing a startup reference voltage further comprises

a current source having an output, and

a PNP transistor having a base, an emitter and a collector, the emitter receiving the output of the current source to establish a base-to-emitter voltage as the startup reference voltage; and

a circuit portion having a second comparator for comparing the band-gap voltage output to the startup reference signal to selectively activate a startup current for starting up the band-gap reference circuit, the start-up current increasing the band-gap voltage output of the band-gap reference circuit.

9. The circuit of claim 8 , wherein the second comparator has hysteresis.

10. The circuit of claim 8 , wherein the circuit portion for comparing the band-gap voltage output to the startup reference signal selectively activates the startup current if the band-gap voltage output is less than the startup reference signal.

11. The circuit of claim 8 , wherein the circuit portion for comparing the band-gap voltage output to the startup reference signal selectively deactivates the startup current if the band-gap voltage output is greater than the startup reference signal.

12. The circuit of claim 8 , wherein the startup current is a sunk current.

13. The circuit of claim 8 , wherein the startup current is a sourced current.

14. A band-gap reference circuit, comprising:

means for generating a band-gap reference voltage, wherein said means for generating includes a first comparator;

means for generating a startup reference signal, wherein said means for generating includes a p-type transistor and a current source providing a current into the p-type transistor thereby generating the start-up reference signal on the p-type transistor;

means for comparing the band-gap reference voltage to the startup reference signal, said means for comparing including a second comparator; and

means for selectively starting the band-gap reference circuit based on the comparing means.

15. The circuit of claim 14 , wherein the means for selectively starting the band-gap reference circuit increases the band-gap reference voltage if the band-gap reference voltage is less than the startup reference signal.