No standby current consuming start up circuit

• US 6,404,252 B1
• Filed: 07/31/2000
• Issued: 06/11/2002
• Est. Priority Date: 07/31/2000
• Status: Active Grant

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Inventors: Wilsch, Harald
• Primary Examiner(s): Callahan, Timothy P.
• Assistant Examiner(s): Luu, An T.
• Application Number:
  US09/630,159
• Time in Patent Office: 680 Days
• Field of Search: 327/142, 327/143, 327/198, 327/538, 327/540, 327/544, 327/545, 327/548, 323/312, 323/315, 323/316
• US Class Current: 327/198
• CPC Class Codes: G05F 3/205 Substrate bias-voltage generators for static stores G11C5/146

Abstract

A start-up circuit for a bias generator circuit includes an oscillator, a power monitoring circuit and a controllable current source. As the power supplies begin to ramp up to their final voltage, the power monitoring circuit monitors power consumed by the oscillator. As the oscillator begins to ring, the power monitoring circuit couples a control signal to the controllable current source, which generates a current used to start-up the bias generator circuit. Once the bias generator circuit has achieved an active operating condition, the start-up circuit is disengaged from the bias circuit by disabling the oscillator. The start-up circuit does not consume any standby current when disabled, and does not effect the operation of the bias generator circuit.

Claims

1. An apparatus that forces a start-up current into a selected node in a current path of a bias circuit when power is activated, comprising:

an oscillator;

a monitor, wherein the monitor produces a control signal when the oscillator is active such that the control signal is related to the total operating current in the oscillator; and

a current source that includes a current control input coupled to the control signal, wherein the current source provides the start-up current at the selected node in response to the control signal such that the current path in the bias circuit is activated into a conducting state when the oscillator consumes power.

2. The apparatus in claim 1, wherein the oscillator includes an oscillator control input that disables the oscillator when activated, whereby power consumption is reduced.

3. The apparatus in claim 1, wherein the oscillator includes an input node, an output node, and a feedback circuit coupled between the input node and the output node, whereby the feedback circuit forms a feedback loop in the oscillator.

4. The apparatus in claim 3, wherein the feedback circuit includes a capacitor.

5. The apparatus in claim 3, further comprising a switch circuit that couples the input node of the oscillator to a potential when activated, wherein the switch circuit is activated when the bias circuit actively conducts such that and the potential is coupled to the input node of the oscillator and the oscillator is disabled to reduce power consumption.

6. The apparatus in claim 5, wherein the switch circuit includes a MOS transistor.

7. The apparatus in claim 5, wherein the switch circuit includes a bipolar transistor.

8. The apparatus in claim 3, wherein the oscillator includes an inverting circuit and the feedback circuit includes a capacitor to ac couple the output node to the input node of the oscillator when the oscillator is active.

9. The apparatus in claim 5, wherein the capacitor isolates the input node from the output node of the oscillator when the oscillator is disabled.

10. The apparatus in claim 3, further comprising a noise injector that couples noise from a power supply line to the input node of the oscillator, wherein the noise coupled to the input node of the oscillator initiates oscillation of the oscillator.

11. The apparatus in claim 10, wherein the noise injector includes a capacitor that couples noise from the power supply line to the input node of the oscillator.

12. The apparatus in claim 10, wherein the noise injector includes a first capacitor connected between a power supply line and the input of the oscillator, and a second capacitor connected between another power supply line and the input of the oscillator such that the first and second capacitors inject charge into the oscillator.

13. The apparatus in claim 1, wherein the monitor includes a transistor that operates as a diode and the transistor is forward biased when the oscillator is active.

14. The apparatus in claim 13, wherein the current source includes another transistor that conducts the start-up current when the transistor for the monitor conducts.

15. The apparatus of claim 5, wherein the activation of the switch is controlled.

16. The apparatus of claim 1, wherein the operation of the current source is controlled.

17. The apparatus of claim 1, wherein the monitor senses one of a current flow and a voltage change in the oscillator when the oscillator is active.

18. The apparatus of claim 1, wherein the monitor includes a first transistor and the current source includes a second transistor such that the first and second transistors form a mirror pair where current flowing in the second transistor is proportional to current flowing in the oscillator when the oscillator is active.

19. The apparatus of claim 1, wherein the current source includes a current amplifier circuit.

20. An apparatus that couples a start-up current into a selected node in a current path of a bias circuit when power is activated, comprising:

an oscillator;

a control means produces a control signal proportional to power consumption in the oscillator;

a current source includes a control input coupled to the control signal such that the current source provides the start-up current proportional to the power consumption of the oscillator; and

means for coupling the start-up current to the selected node such that the current path in the bias circuit is forced into a conducting state, whereby said bias circuit is activated.

21. The apparatus in claim 20, further comprising:

means for producing a bias active signal when the bias circuit is in active operation; and

means for disabling the oscillator in response to the active signal such that the oscillator is disabled when the bias circuit is active and power consumption is reduced.

22. The apparatus in claim 20, further comprising means for coupling a noise signal into the oscillator circuit to initiate oscillations in the oscillator.

23. A method for forcing a bias circuit into an active state of operation, comprising:

producing an oscillator active signal when an oscillator is oscillating in an oscillator circuit;

producing a start-up current in response to the oscillator active signal;

feeding the start-up current into the bias circuit to force the bias circuit into the active state of operation;

producing a bias active signal when the bias circuit is in the active state of operation; and

disabling the oscillator in response to said bias active signal such that the oscillator is inactive when the bias circuit is active and power consumption is reduced.

24. The method of claim 23, further comprising injecting noise into the oscillator circuit to initiate oscillations in the oscillator.