Power-up circuit for analog circuits

• US 6,285,223 B1
• Filed: 05/16/2000
• Issued: 09/04/2001
• Est. Priority Date: 05/16/2000
• Status: Expired due to Term

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Agere Systems Guardian Corp. (Broadcom, Inc.)
• Inventors: Smith, Malcolm H.
• Primary Examiner(s): ZWEIZIG, JEFFERY SHAWN
• Application Number:
  US09/571,912
• Time in Patent Office: 476 Days
• Field of Search: 327/142, 327/143, 327/538, 327/543
• US Class Current: 327/143
• CPC Class Codes: G05F 3/30 Regulators using the difference between the base-emitter voltages of two bipolar transistors operating at different current densities G05F3/26 takes precedence

Abstract

A start-up circuit for supplying current to an analog circuit. The start-up circuit comprises a capacitor connected to a current mirror. A power-up signal input to the start-up circuit causes the capacitor to discharge to the current mirror thereby causing the current mirror to provide a current to the analog circuit.

Claims

1. A start-up circuit for supplying current to an analog circuit comprising:

a capacitor connected to a current mirror, where upon a power-up signal input to the start-up circuit causes the capacitor to discharge to the current mirror, thereby causing the current mirror to provide a current to the analog circuit.

2. A semiconductor device comprising a start-up circuit as in claim 1.

4. The start-up circuit of claim 1 wherein the capacitor is a transistor.

5. The start-up circuit of claim 1 wherein the start-up circuit is used to power a low power analog circuit.

6. The start-up circuit of claim 1 wherein the start-up circuit is used to power a band gap reference circuit.

7. The start-up circuit of claim 1 wherein the start-up circuit is used to power a current steering circuit for a digital to analog conversion circuit.

3. A start-up circuit for providing a current to an analog circuit in response to a power-down signal wherein the start-up circuit comprises:

at least five transistors each having a gate, a drain and a source;

a capacitor having a first electrode and a second electrode, the first capacitor electrode receiving an input voltage and the second capacitor electrode connected in series to the first transistor drain;

the first transistor source connected to ground;

the first transistor gate receiving a power-down signal input;

the second capacitor electrode further connected to the second transistor drain;

the second transistor drain further connected to the third transistor drain;

the second transistor gate receiving the power-down signal;

the third transistor source connected to the fourth transistor source;

the fourth transistor source receiving a voltage input;

the fourth transistor drain connected to the fifth transistor gate and to the third transistor gate;

the fourth transistor gate receiving an inverted power-down signal;

the fifth transistor gate further connected to the third transistor gate;

the fifth transistor source receiving a voltage input; and

the fifth transistor drain providing a start-up current to the analog circuit.

8. The start-up circuit of claim 3 wherein the current flowing through the fifth transistor is larger than the current flowing through the third transistor by a factor equal to the channel-width-to-channel-length-ratio of the third and fifth transistors.

9. A start-up circuit for supplying current to an analog circuit comprising:

means for receiving a power-down signal, the receiving means charging to a voltage;

means for providing a reference current wherein the reference current means is supplied with a current from the receiving means; and

means for mirroring current from the reference means;

wherein the current mirroring means charges one or more nodes of the analog circuit.

10. The start-up circuit of claim 9 wherein the receiving means is a transistor.

11. The start-up circuit of claim 9 wherein the current mirror reference means is a diode-connected transistor.

12. The start-up of claim 9 wherein the start-up circuit is used to power a low power analog circuit.

13. The start-up circuit of claim 9 wherein the start-up circuit is used to power a band gap reference circuit.

14. The start-up circuit of claim 9 wherein the start-up circuit is used to power a current steering circuit for a digital to analog conversion circuit.

15. A semiconductor device comprising a start-up circuit as in claim 9.