Low voltage, low power oscillator having voltage level shifting circuit

• US 5,552,751 A
• Filed: 06/06/1995
• Issued: 09/03/1996
• Est. Priority Date: 06/06/1995
• Status: Expired due to Fees

• Current Assignee: Microchip Technology Incorporated
• Original Assignee: Microchip Technology Incorporated
• Inventors: Cooper, Russell E.
• Primary Examiner(s): MIS, DAVID C
• Application Number:
  US08/469,176
• Time in Patent Office: 455 Days
• Field of Search: 331/116 FE, 331/185, 331/116 R, 331/117 R, 331/117 FE, 331/57, 331/158, 331/173, 331/186
• US Class Current: 331/116.0FE
• CPC Class Codes: H03K 3/012 Modifications of generator to improve response time or to decrease power consumption
• CPC Class Codes: H03K 3/3545 Stabilisation of output, e.g. using crystal

Abstract

An oscillator circuit (30, 40) for starting-up and operating at low voltages has been provided. The oscillator circuit includes an inverter circuit(31, 41) coupled across first and second terminals of a resonant circuit (14). The inverter circuit includes a push-pull driver stage having a P-channel transistor (18) and an N-channel transistor (20). The common drain electrodes of each are coupled to the second terminal of the resonant circuit. The source electrodes of the P- and N-channel transistors are respectively coupled to first and second supply voltage terminals. The gate electrode of the first transistor is coupled to the first terminal of resonant circuit. The inverter circuit further includes a circuit (32, 42) for shifting the voltage level applied to the gate electrode of the second transistor, relative to the voltage applied to the gate electrode of the first transistor, by a predetermined voltage. This has the effect of reducing the required operating voltage range of the inverter circuit while still maintaining both transistors active.

Claims

1. An oscillator circuit for providing an output signal that oscillates at a predetermined frequency, the oscillator circuit including an inverter circuit that is coupled across first and second terminals of a resonant circuit, the inverter circuit including first and second transistors having common drain electrodes coupled to the output of the oscillator circuit and to the second terminal of the resonant circuit, the source electrodes of the first and second transistors respectively coupled to first and second supply voltage terminals, the gate electrode of one of the transistors coupled to the first terminal of the resonant circuit, the improvement comprising:

circuit means coupled between the first terminal of the resonant circuit and the gate electrode of the other transistor for level shifting the voltage applied to the gate electrode of the other transistor relative to the voltage applied to the gate electrode of the one transistor to maintain the first and second transistors active and thereby allow the oscillator circuit to start-up and operate at relatively low supply voltages.

2. The oscillator circuit according to claim 1 wherein the minimum difference between voltages applied to the first and second supply voltage terminals to maintain the first and second transistors active is the maximum of the threshold voltages of the first and second transistors, less a threshold voltage applicable to said circuit means.

3. The oscillator circuit according to claim 1 wherein said circuit means includes an N-channel transistor having drain, source and gate electrodes, said drain electrode and said source electrode of said N-channel transistor respectively coupled between said first and second supply voltage terminals, said source electrode of said N-channel transistor coupled to the gate electrode of the first transistor, said gate electrode of said N-channel transistor coupled to the first terminal of the resonant circuit.

4. The oscillator circuit according to claim 1 wherein said circuit means includes a P-channel transistor having drain, source and gate electrodes, said source and drain electrodes of said P-channel transistor respectively coupled between said first and second supply voltage terminals, said source electrode of said P-channel transistor coupled to the gate electrode of the second transistor, said gate electrode of said N-channel transistor coupled to the first terminal of the resonant circuit.

5. The oscillator circuit according to claim 1 further including means for alternatively operating the oscillator circuit in an on or off state.

6. An oscillator circuit including an inverter circuit and a resonant circuit for starting-up and operating at low voltages, the inverter circuit being coupled across first and second terminals of the resonant circuit, the inverter circuit comprising:

a push-pull output driver stage including first and second complementary transistors each having drain, source and gate electrodes, said source electrodes said first and second transistors respectively coupled to first and second supply voltage terminals, said drain electrodes of said first and second transistors coupled to the second terminal of the resonant circuit, said gate electrode of said second transistor coupled to the first terminal of the resonant circuit; and

voltage level shifting means coupled between the first terminal of the resonant circuit and said gate electrode of said first transistor for shifting the voltage applied to said gate electrode of said first transistor relative to the voltage applied to said gate electrode of said second transistor.

7. The oscillator circuit according to claim 6 wherein the minimum difference between voltages applied to the first and second supply voltage terminals to maintain the first and second transistors active is the maximum of the threshold voltages of the first and second transistors, less a threshold level of said voltage level shifting means.

8. The oscillator circuit according to claim 6 wherein said voltage level shifting means includes a source follower N-channel transistor.

9. The oscillator circuit according to claim 6 wherein said voltage level shifting means includes a source follower P-channel transistor.

10. The oscillator circuit according to claim 6 further including means for alternately operating the oscillator circuit in an on or off state.

11. A push-pull inverter circuit having an input and an output for operating at low voltages, comprising:

first and second complementary transistors, said first transistor having current carrying electrodes coupled between the output of the inverter circuit and a first supply voltage terminal, said second transistor having current carrying electrodes coupled between the output of the inverter circuit and a second supply voltage terminal, a control electrode of the first transistor coupled to the input of the inverter circuit;

a resonant circuit coupled across the output of the inverter circuit and the control electrodes of the first and second transistors, and

voltage level shifting circuit means coupled between the input of the inverter circuit and a control electrode of the second transistor for shifting the voltage applied to the control electrode of the second transistor relative to the voltage applied to the control electrode of the first transistor, thereby allowing both transistors to remain active at low supply voltages so as to initiate oscillation upon powering up the inverter circuit.

12. The inverter circuit according to claim 11 wherein the minimum difference between voltages applied to the first and second supply voltage terminals to maintain the first and second transistors active is the maximum of the threshold voltages of the first and second transistors, less a threshold voltage of the voltage level shifting circuit means.

13. The inverter circuit according to claim 11 wherein said voltage level shifting means includes a source follower N-channel transistor for shifting the voltage applied to the control electrode of the second transistor by the threshold voltage of said N-channel transistor.

14. The inverter circuit according to claim 11 wherein said voltage level shifting means includes a source follower P-channel transistor for shifting the voltage applied to the control electrode of the second transistor by the threshold voltage of said P-channel transistor.