High voltage generator

• US 5,801,577 A
• Filed: 12/11/1996
• Issued: 09/01/1998
• Est. Priority Date: 12/26/1995
• Status: Expired due to Term

• Current Assignee: SGS Thomson Microelectronics SA (STMicroelectronics NV)
• Original Assignee: SGS Thomson Microelectronics SA (STMicroelectronics NV)
• Inventors: Tailliet, Fran.cedilla.ois
• Primary Examiner(s): Callahan, Timothy P.
• Assistant Examiner(s): ZWEIZIG, JEFFERY SHAWN
• Application Number:
  US08/762,677
• Time in Patent Office: 629 Days
• Field of Search: 307/110, 327/530, 327/534, 327/535, 327/536, 327/537, 327/545, 327/546, 327/548
• US Class Current: 327/536
• CPC Class Codes: H02M 3/07 using capacitors charged and discharged alternately by semiconductor devices with control electrode , e.g. charge pumps

Abstract

A circuit including a network of capacitors and switching transistors having two modes of functioning. The first mode isolates all the capacitors and simultaneously charges them to the level of the supply voltage. The second mode connects all these capacitors in series between the supply voltage Vdd and an output node of the network in order to instantaneously increase the voltage level of this output node to a voltage level that is greater than the supply voltage Vdd. The capacitors are all connected in series by transistors that are placed between them and controlled by a signal that has a peak voltage that is greater than the voltage to be switched to the output node of the network.

Claims

1. A circuit for generating a voltage having a peak amplitude that is greater than a voltage level of a supply voltage, comprising:

a network of capacitors having an output node; and

a control circuit, for controlling a plurality of switching transistors having two modes of functioning, a first mode for isolating all the capacitors in the network and simultaneously charging them to the voltage level of the supply voltage, and a second mode for connecting all the capacitors in the network in series between the supply voltage and the output node of the network to instantaneously increase a voltage level of the output node to a voltage level that is greater than the voltage level of the supply voltage;

wherein switching transistors that are placed between each capacitor in the network so as to connect all the capacitors in series are controlled by a first signal having a peak voltage that is greater than the voltage level to be switched to the output node of the network.

2. The circuit of claim 1, wherein, for each respective capacitor in the network of capacitors, the control circuit includes:

a first switching transistor connected between the supply voltage and a first terminal of the respective capacitor;

a second switching transistor connected between a second terminal of the respective capacitor and a reference voltage, the first and second switching transistors being controlled by their gates by a second signal; and

a third switching transistor connected between the first terminal of the respective capacitor and the second terminal of a following capacitor that is next in the network of capacitors, the third switching transistor being controlled by its gate by the first signal, the output node of the network being supplied by the third switching transistor that is connected in series with the first terminal of a last capacitor in the network of capacitors.

3. The circuit of claim 2, wherein the plurality of switching transistors are N-type transistors and the first and second switching transistors are natural N-type transistors.

4. The circuit of claim 2, wherein the third transistor connected in series with the first terminal of the last capacitor is a natural N-type transistor and limits the voltage level it switches based on an amplitude of the first signal that is applied to its gate.

5. The circuit of claim 4, further comprising a fourth transistor, controlled by the second signal, connected between the output node of the network and the reference voltage, to isolate the output node and a pull-down of the output node to a level of the reference voltage during the charging of the capacitors.

6. The circuit of claim 2, further comprising an additional switching transistor, controlled by the first control signal, to connect the second terminal of a first capacitor in the network to the supply voltage when the network of capacitors are connected in series.

7. The circuit of claim 1, further comprising:

a Schenkel type charge pump for supplying a regulated voltage; and

first and second level translation circuits to receive the regulated output voltage and a third signal having a peak amplitude of the supply voltage and generate the first and second signals.

12. The circuit of claim 1, wherein a peak amplitude of the output signal is limited to the peak amplitude of the second signal.

8. A high voltage charge pump type generator including a network of capacitors and switching transistors that are controlled by two non-overlapping clock signals that switch between a reference voltage level of a reference voltage and a supply voltage level of a supply voltage and two other clock signals that respectively switch substantially in phase with the two non-overlapping clock signals but between the reference voltage level and a voltage level that is greater than the supply voltage level, wherein the two other clock signals are respectively supplied by a circuit for generating a peak voltage comprising:

a second network of capacitors having an output node; and

a control circuit, for controlling a plurality of switching transistors having two modes of functioning, a first mode for isolating all the capacitors in the second network and simultaneously charging them to the supply voltage level, and a second mode for connecting all the capacitors in the second network in series between the supply voltage and the output node of the second network to instantaneously increase a voltage level of the output node to a voltage level that is greater than the supply voltage level;

wherein switching transistors that are placed between each capacitor in the second network so as to connect all the capacitors in series are controlled by a first signal of the two other clock signals having a peak voltage that is greater than the voltage level to be switched to the output node of the network.

9. The high voltage charge pump of claim 8, wherein the high voltage charge pump is formed in an integrated circuit.

10. The high voltage charge pump of claim 9, wherein the integrated circuit is included in a smart card.

11. A circuit to generate an output signal having an amplitude that is greater than a supply voltage, the circuit comprising:

a plurality of capacitors forming a network of capacitors, each capacitor in the network having a first terminal and a second terminal, the first terminal of each capacitor being coupled to the supply voltage and the second terminal of each capacitor being coupled to a reference voltage;

a plurality of switching transistors including a plurality of series switching transistors, each respective series switching transistor being coupled in series between the first terminal of a respective capacitor in the network and the second terminal of a next capacitor that is next in the network, a last series switching transistor being coupled between the first terminal of a last capacitor in the network and an output of the network; and

a control circuit, coupled to each of the plurality of switching transistors, to generate a first signal that isolates each capacitor in the network and simultaneously charges each capacitor to a voltage level of the supply voltage and a second signal that connects each capacitor in the network in series between the supply voltage and the output of the network to generate the output signal;

wherein the first signal has a peak amplitude that is approximately equal to the supply voltage, the second signal has a peak amplitude that is greater than the output signal, and the first signal is in phase opposition to the second signal.

13. The circuit of claim 11, wherein the plurality of switching transistors further includes:

a plurality of second switching transistors, a respective second switching transistor being coupled between the supply voltage and the first terminal of each respective capacitor in the network, each respective second switching transistor being coupled to the first signal; and

a plurality of third switching transistors, a respective third switching transistor being coupled between the reference voltage and the second terminal of each respective capacitor in the network, each respective third switching transistor being coupled to the first signal;

wherein each respective series switching transistor is coupled to the second signal.

14. The circuit of claim 13, wherein the plurality switching transistors are N-type transistors and the plurality of second switching transistors and the plurality of third switching transistors are natural N type transistors.

15. The circuit of claim 14, wherein the last series switching transistor is a natural N-type transistor that limits a peak amplitude of the output signal to the peak amplitude of the second signal.

16. The circuit of claim 13, further comprising:

an output transistor coupled between the output of the network and the reference voltage, the output transistor being coupled to the first signal to isolate the output of the network and pull down the output of the network to the reference voltage during charging of the plurality of capacitors.

17. The circuit of claim 16, further comprising:

an input transistor coupled between the supply voltage and the first terminal of a first capacitor in the network, the input transistor being coupled to the second signal.

18. The circuit of claim 17, wherein the plurality switching transistors are N-type transistors, the plurality of second switching transistors and the plurality of third switching transistors are natural N type transistors, and the last series switching transistor is a natural N-type transistor that limits a peak amplitude of the output signal to the peak amplitude of the second signal.

19. The circuit of claim 13, further comprising:

an input transistor coupled between the supply voltage and the first terminal of a first capacitor in the network, the input transistor being coupled to the second signal.

20. A high voltage generator comprising:

an oscillator circuit to generate an oscillating clock signal;

a Schenkel type charge pump including an output transistor to supply an output voltage; and

a phase generation circuit coupled between the oscillator circuit and the charge pump to receive the oscillating clock signal and generate two pairs of signals including a first pair of signals and a second pair of signals, the first pair of signals including a first signal and a second signal that are complementary to each other, non-overlapping, and switch between a reference voltage level of a reference voltage and a supply voltage level of a supply voltage, the second pair of signals including a third signal and a fourth signal corresponding to the first and second signals, respectively, and switching between the reference voltage level and a third voltage level when the first and second signals, respectively, are at the supply voltage level, the third and fourth signals having an amplitude that is greater than a threshold voltage of the output transistor of the charge pump in addition to a body effect of the output transistor, wherein the phase generation circuit includes;

a first network of capacitors coupled to a first plurality of switching transistors having two modes of operation, a first mode isolating each of the capacitors in the first network and simultaneously charging each of the capacitors to the supply voltage level, and a second mode connecting each of the capacitors in the first network in series between the supply voltage and an output node of the first network to provide the third signal; and

a second network of capacitors coupled to a second plurality of switching transistors having two modes of operation, a third mode isolating each of the capacitors in the second network and simultaneously charging each of the capacitors to the supply voltage level, and a fourth mode connecting each of the capacitors in the second network in series between the supply voltage and an output node of the second network to provide the fourth signal.

21. The generator of claim 20, further comprising:

a regulation circuit, coupled between the charge pump and the oscillator circuit, to receive the output voltage of the charge pump and reintroduce the output voltage to the oscillator circuit independent of variations in the supply voltage.

22. The generator of claim 21, wherein the oscillator circuit includes:

a first output terminal to provide the oscillating clock signal to the phase generation circuit;

a second output terminal to provide a start/stop signal to the phase generation circuit that one of stops and starts the charge pump;

a first input terminal to receive a first slave signal from the phase generation circuit and increase an oscillation frequency of the oscillating clock signal; and

a second input terminal to receive a second slave signal from the phase generation circuit and decrease the oscillation frequency of the oscillating clock signal.

23. The generator of claim 22, wherein the phase generation circuit further includes:

a logic circuit to receive the oscillating clock signal and the start/stop signal and provide a base clock signal that follows the oscillating clock signal when the start/stop signal has a first value, the base clock signal having a fixed value when the start/stop signal has a second value.

24. The generator of claim 23, wherein the phase generation circuit further includes:

a first circuit to receive the base clock signal and the second pair of signals and generate the first pair of signals and a pair of switching control signals, the pair of switching control signals including a first switching control signal corresponding to the third signal and a second switching control signal corresponding to the fourth signal; and

a second circuit, coupled to the first circuit, to receive the first and second switching control signals and generate the third and fourth signals.

25. The generator of claim 24, wherein the first circuit includes:

a switching control circuit to receive the base clock signal and generate first and second control signals for the first and second signals, respectively;

a first signal generation circuit to receive the first control signal and the third signal and generate the first signal and the first switching control signal; and

a second signal generation circuit to receive the second control signal and the fourth signal and generate the second signal and the second switching control signal.

26. The generator of claim 24, wherein the second circuit includes:

a regulated voltage generator to provide a regulated output voltage having an amplitude;

a first level translator, coupled to the regulated voltage generator, to receive the first switching control signal and provide first and second mode signals, the first mode signal having a peak amplitude approximately equal to amplitude of the regulated output voltage, and the second mode signal having a peak amplitude approximately equal to twice the amplitude of the regulated output voltage;

a first multiplier, coupled to the first level translator, to receive the first and second mode signals and generate the third signal;

a second level translator, coupled to the regulated voltage generator, to receive the second switching control signal and provide third and fourth mode signals, the third mode signal having a peak amplitude approximately equal to amplitude of the regulated output voltage, and the fourth mode signal having a peak amplitude approximately equal to twice the amplitude of the regulated output voltage; and

a second multiplier, coupled to the second level translator, to receive the third and fourth mode signals and generate the fourth signal.

27. The generator of claim 26, wherein the regulated voltage generator includes:

a ring oscillator;

a second Schenkel type charge pump coupled to the ring oscillator to provide the regulated output voltage on an output terminal; and

a regulator coupled to the output terminal of the second charge pump and an input of the ring oscillator.

28. The generator of claim 26, wherein the second mode signal has a peak amplitude that is at least equal to a peak amplitude of the third signal.

29. The generator of claim 26, wherein the generator is formed in an integrated circuit that is included in a smart card.

30. The generator of claim 20, wherein the phase generation circuit includes a slave circuit to generate first and second slave signals based upon an amplitude and a phase of the first and second pairs of signals.

31. The generator of claim 20, wherein the third and fourth signals are limited to a voltage level that is less than a gate oxide breakdown voltage of the output transistor of the charge pump.

32. A method of controlling a charge pump, comprising the steps of:

(A) generating first and second signals that are complementary to each other, non-overlapping, and switch between a reference voltage level of a reference voltage and a supply voltage level of a supply voltage;

(B) isolating and simultaneously charging each capacitor in a first network of capacitors to the supply voltage level when the first signal is at the reference voltage level;

(C) isolating and simultaneously charging each capacitor in a second network of capacitors to the supply voltage level when the second signal is at the reference voltage level;

(D) connecting each capacitor in the first network of capacitors in series between the supply voltage and an output node of the first network when the first signal is at the supply voltage level to generate a third signal, synchronized to the first signal, having a peak voltage level greater than the supply voltage level;

(E) connecting each capacitor in the second network of capacitors in series between the supply voltage and an output node of the second network when the second signal is at the supply voltage level to generate a fourth signal, synchronized to the fourth signal, having a peak voltage level greater than the supply voltage level; and

(F) limiting the peak voltage levels of the third and fourth signals to be less than a gate oxide breakdown voltage of an output transistor of the charge pump.

33. The method of claim 32, wherein the peak voltage levels of the third and fourth signals are greater than a sum of a threshold voltage of the output transistor of the charge pump and a body effect of a drain voltage of the output transistor.

34. The method of claim 32, wherein step (A) includes a step of adjusting a frequency of the first and second signals in response to variations in the supply voltage level.

35. The method of claim 32, wherein step (B) includes a step of generating a first switching control signal having a voltage level that is approximately equal to the supply voltage level to isolate and simultaneously charge each capacitor in the first network.

36. The method of claim 35, wherein step (D) includes a step of generating a second switching control signal having a voltage level that is approximately twice the supply voltage level to connect each capacitor in the first network in series.

37. The method of claim 36, wherein the first switching control signal is opposite in phase to the second switching control signal and the voltage level of the second switching control signal is greater than the peak voltage level of the third signal.

38. The method of claim 32, wherein step (B) includes the steps of:

isolating an output of the first network of capacitors when the first signal is at the reference voltage level; and

pulling the output of the first network of capacitors down to the reference voltage level when the first signal is at the reference voltage level.

39. A voltage generator comprising:

an oscillator to generate an oscillating clock signal;

a Schenkel type charge pump to supply an output voltage that is greater than a supply voltage level of a supply voltage;

a principal signal generator, coupled to the oscillator and the charge pump, to receive the oscillating clock signal, generate first and second signals that are complementary to each other, non-overlapping, and switch between a reference voltage level of a reference voltage and the supply voltage level, and provide the first and second signals to the charge pump;

a first network of capacitors and switching transistors coupled to the charge pump, to generate a third signal and provide the third signal to the charge pump, the third signal corresponding to the first signal and switching between the reference voltage level and a third voltage level that is greater than the supply voltage level when the first signal is at the supply voltage level;

a second network of capacitors and switching transistors coupled to the charge pump, to generate a fourth signal and provide the fourth signal to the charge pump, the fourth signal corresponding to the second signal and switching between the reference voltage level and the third voltage level when the second signal is at the supply voltage level; and

secondary signal generation means, coupled to the principle signal generator and the first and second networks of capacitors and switching transistors, for generating first and second pairs of switching control signals to respectively generate the third and fourth signals.

40. The voltage generator of claim 39, further comprising:

a regulation circuit, coupled to the charge pump and the oscillator circuit, to receive the output voltage of the charge pump and reintroduce the output voltage to the oscillator circuit independent of variations in the supply voltage.

41. The voltage generator of claim 39, further comprising:

an enslavement circuit, coupled to the oscillator, to receive the first, second, third and fourth signals, and at least one switching control signal from each of the first and second pairs of switching control signals, and one of increase and decrease a frequency of the oscillating clock signal dependent on variations in the supply voltage level.

42. The voltage generator of claim 39, wherein the charge pump supplies the output voltage on an output transistor, and the secondary signal generation means includes:

means for limiting a peak amplitude of the third and fourth signals to a voltage level that is less than a gate oxide breakdown voltage of the output transistor.

43. The voltage generator of claim 39, wherein the secondary signal generation means includes:

a regulated voltage generator;

a first level translator, coupled to the regulated voltage generator and the principal signal generator, that generates the first pair of signals; and

a second level translator, coupled to the regulated voltage generator and the principal signal generator, that generates the second pair of signals.