Level shifting flip-flop

• US 8,378,728 B1
• Filed: 06/03/2012
• Issued: 02/19/2013
• Est. Priority Date: 06/03/2012
• Status: Active Grant

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: Goyal, Gaurav, Mahajan, Abhishek, Malhan, Bipin B.
• Primary Examiner(s): O NEILL, PATRICK
• Application Number:
  US13/487,243
• Time in Patent Office: 261 Days
• Field of Search: 327199-203, 327208-214, 327/218, 327223-225, 327/333, 326/62, 326/80, 326/81, 326 93- 98
• US Class Current: 327/203
• CPC Class Codes: H03K 3/35625 using complementary field-effect transistors

Abstract

A level shifting flip-flop for generating a level-shifted output signal based on an input signal includes a master stage and a slave stage. The slave stage has an integrated level shifting circuit. The slave stage level shifts a signal as it passes through the flip-flop, which eliminates the need of level shifting the signal after it is output from the flip-flop.

Claims

1. A flip-flop circuit for generating a level-shifted output signal based on an input signal and a clock signal, comprising:

a master stage for receiving the input signal and the clock signal and generating an inverted clock signal, an internal clock signal, and a master stage output signal based on the input signal and the clock signal, the master stage including;

a first transistor having a source terminal that receives a first supply voltage, and a gate terminal for receiving the input signal;

a second transistor having a source terminal connected to a drain terminal of the first transistor, and a gate terminal for receiving the internal clock signal;

a third transistor having a drain terminal connected to a drain terminal of the second transistor, and a gate terminal that receives the inverted clock signal;

a fourth transistor having a drain terminal connected to a source terminal of the third transistor, a gate terminal for receiving the input signal, and a source terminal connected to ground;

a fifth transistor having a source terminal that receives the first supply voltage, and a gate terminal connected to the drain terminals of the second and third transistors;

a sixth transistor having a drain terminal connected to a drain terminal of the fifth transistor, for generating a clocked input signal, a gate terminal connected to the gate terminal of the fifth transistor, and a source terminal connected to ground;

a first inverter having an input connected to the drain terminals of the fifth and sixth transistors for receiving the clocked input signal, and an output that provides the master stage output signal;

a seventh transistor having a source terminal that receives the first supply voltage, and a gate terminal connected to the drain terminals of the fifth and sixth transistors for receiving the clocked input signal;

an eighth transistor having a source terminal connected to a drain terminal of the seventh transistor, and a gate terminal that receives the inverted clock signal;

a ninth transistor having a drain terminal connected to a drain terminal of the eighth transistor, and a gate terminal that receives the internal clock signal,

wherein the drain terminals of the eighth and ninth transistors are connected to the gate terminals of the fifth and sixth transistors; and

a tenth transistor having a drain terminal connected to a source terminal of the ninth transistor, a gate terminal connected to the drain terminals of the fifth and sixth transistors for receiving the clocked input signal, and a source terminal connected to ground;

a second inverter having an input that receives the clock signal and an output that provides the inverted clock signal; and

a third inverter having an input connected to the output of the second inverter and receiving the inverted clock signal, and an output that provides the internal clock signal; and

a slave stage, connected to the master stage, for generating the level-shifted output signal, the slave stage including;

a seventeenth transistor having a source terminal that receives the first supply voltage, and a gate terminal connected to the output of the first inverter and receiving the master stage output signal;

an eighteenth transistor having a source terminal connected to a drain terminal of the seventeenth transistor, and a gate terminal that receives the inverted clock signal;

a nineteenth transistor having a drain terminal connected to a drain terminal of the eighteenth transistor, and a gate terminal that receives the internal clock signal;

a twentieth transistor having a drain terminal connected to a source terminal of the nineteenth transistor, a gate terminal connected to the gate terminal of the seventeenth transistor and the output of the first inverter, and a source terminal connected to ground;

a twenty-first transistor having a gate terminal that receives the internal clock signal;

a twenty-second transistor having a drain terminal connected to a source terminal of the twenty-first transistor, a gate terminal connected to the output of the first inverter and receiving the master stage output signal, and a source terminal connected to ground;

a twenty-third transistor having a source terminal connected to a drain terminal of the twenty-first transistor, a gate terminal that receives the inverted clock signal, and a drain terminal connected to the drain terminals of the eighteenth and nineteenth transistors;

a twenty-fourth transistor having a drain terminal connected to the drain terminal of the twenty-third transistor, and a gate terminal that receives the internal clock signal;

a twenty-fifth transistor having a source terminal that receives the first supply voltage, and a drain terminal connected to a source terminal of the twenty-fourth transistor;

a twenty-sixth transistor having a source terminal that receives a second supply voltage, a gate terminal connected to a gate terminal of the twenty-fifth transistor, and a drain terminal connected to the drain terminal of the twenty-first transistor;

a twenty-seventh transistor having a drain terminal connected to the drain terminal of the twenty-sixth transistor, and a gate terminal that receives the inverted clock signal;

a twenty-eighth transistor having a drain terminal connected to a source terminal of the twenty-seventh transistor, a source terminal connected to ground, and a gate terminal connected to the gate terminals of the twenty-fifth and twenty-sixth transistors;

a twenty-ninth transistor having a source terminal that receives the second supply voltage, a gate terminal connected to the drain terminal of the twenty-first transistor and the source terminal of the twenty-third transistor, and a drain terminal connected to the gate terminals of the twenty-fifth and twenty-sixth transistors;

a thirtieth transistor having a drain terminal connected to the drain terminal of the twenty-ninth transistor, a gate terminal connected to the drain terminals of the eighteenth and nineteenth transistors, and a source terminal connected to ground; and

a fourth inverter connected between the second supply voltage and ground, wherein the fourth inverter has an input connected to the drain terminals of the twenty-ninth and thirtieth transistors, and an output that provides the level shifted output signal.

2. The flip-flop circuit of claim 1, wherein the first inverter comprises:

an eleventh transistor having a source terminal that receives the first supply voltage, and a gate terminal connected to the drain terminals of the fifth and sixth transistors for receiving the clocked input signal; and

a twelfth transistor having a drain terminal connected to the drain terminal of the eleventh transistor, a gate terminal connected to the gate terminal of the eleventh transistor, and a source terminal connected to ground, wherein the master stage output signal is provided at the drain terminals of the eleventh and twelfth transistors.

3. The flip-flop circuit of claim 2, wherein the second inverter comprises:

a thirteenth transistor having a source terminal that receives the first supply voltage, a gate terminal for receiving the clock signal, and a drain terminal for generating the inverted clock signal; and

a fourteenth transistor having a drain terminal connected to the drain terminal of the thirteenth transistor, a gate terminal connected to the gate terminal of the thirteenth transistor, and a source terminal connected to ground; and

wherein the third inverter comprises;

a fifteenth transistor having a source terminal that receives the first supply voltage, a gate terminal connected to the drain terminals of the thirteenth and fourteenth transistors for receiving the inverted clock signal, and a drain terminal for generating the internal clock signal; and

a sixteenth transistor having a drain terminal connected to the drain terminal of the fifteenth transistor, a gate terminal connected to the gate terminal of the fifteenth transistor, and a source terminal connected to ground.

4. The flip-flop circuit of claim 3, wherein the fourth inverter comprises:

a thirty-first transistor having a source terminal that receives the second supply voltage, and a gate terminal connected to the drain terminals of the twenty-ninth and thirtieth transistors; and

a thirty-second transistor having a drain terminal connected to a drain terminal of the thirty-first transistor, for generating the level-shifted output signal, a gate terminal connected to the gate terminal of the thirty-first transistor, and a source terminal connected to ground.

5. The flip-flop circuit of claim 1, wherein the first, second, fifth, seventh, eighth, seventeenth, eighteenth, twenty-fourth, twenty-fifth, twenty-sixth, and twenty-ninth transistors are p-channel metal-oxide semiconductor (PMOS) transistors.

6. The flip-flop circuit of claim 5, wherein the third, fourth, sixth, ninth, tenth, nineteenth, twentieth, twenty-first, twenty-second, twenty-third, twenty-seventh, twenty-eighth, and thirtieth transistors are n-channel metal-oxide semiconductor (NMOS) transistors.

7. The flip-flop circuit of claim 1, wherein the second supply voltage is at least one of greater and smaller than the first supply voltage.

8. A flip-flop circuit for generating a level-shifted output signal based on an input signal and a clock signal, comprising:

a master stage for receiving the input signal and the clock signal and generating an inverted clock signal, an internal clock signal, and a master stage output signal based on the input signal and the clock signal; and

a slave stage, connected to the master stage, for generating the level-shifted output signal based on the inverted clock signal, the internal clock signal, and the master stage output signal, the slave stage including;

a first transistor having a source terminal that receives a first supply voltage, and a gate terminal that receives the master stage output signal;

a second transistor having a source terminal connected to a drain terminal of the first transistor, and a gate terminal that receives the inverted clock signal;

a third transistor having a drain terminal connected to a drain terminal of the second transistor, and a gate terminal that receives the internal clock signal,

wherein a clocked input signal is generated at a node between the drains of the second and third transistors;

a fourth transistor having a drain terminal connected to a source terminal of the third transistor, a gate terminal connected to the gate terminal of the first transistor and receiving the master stage output signal, and a source terminal connected to ground;

a fifth transistor having a gate terminal that receives the internal clock signal;

a sixth transistor having a drain terminal connected to a source terminal of the fifth transistor, a gate terminal connected to the gate terminal of the first transistor for receiving the master stage output signal, and a source terminal connected to ground;

a seventh transistor having a source terminal connected to a drain terminal of the fifth transistor, a gate terminal that receives the inverted clock signal, and a drain terminal connected to the drain terminals of the second and third transistors;

an eighth transistor having a drain terminal connected to the drain terminal of the seventh transistor, and a gate terminal for receiving the internal clock signal;

a ninth transistor having a source terminal that receiver the first supply voltage, and a drain terminal connected to a source terminal of the eighth transistor;

a tenth transistor having a source terminal that receives a second supply voltage, a gate terminal connected to a gate terminal of the ninth transistor, and a drain terminal connected to the source terminal of the seventh transistor;

an eleventh transistor having a drain terminal connected to the drain terminal of the tenth transistor, and a gate terminal that receives the inverted clock signal;

a twelfth transistor having a drain terminal connected to a source terminal of the eleventh transistor, a source terminal connected to ground, and a gate terminal connected to the gate terminal of the tenth transistor;

a thirteenth transistor having a source terminal that receives the second supply voltage, a gate terminal connected to the drain terminal of the fifth transistor and the source terminal of the seventh transistor, and a drain terminal connected to the gate terminal of the ninth transistor;

a fourteenth transistor having a drain terminal connected to the drain terminal of the thirteenth transistor, a source terminal connected to ground, and a gate terminal connected to the drain terminals of the second and third transistors for receiving the clocked input signal, wherein an inverted level-shifted output signal is output at the drain terminals of the thirteenth and fourteenth transistors; and

a first inverter having an input connected to the drain terminals of the thirteenth and fourteenth transistors for receiving the inverted level shifted output signal, and an output terminal that provides the level shifted output signal.

9. The flip-flop circuit of claim 8, wherein the first inverter comprises:

a fifteenth transistor having a source terminal that receives the second supply voltage, and a gate terminal connected to the drain terminals of the thirteenth and fourteenth transistors for receiving the inverted level-shifted output signal; and

a sixteenth transistor having a drain terminal connected to a drain terminal of the fifteenth transistor, a source terminal connected to ground, and a gate terminal connected to drain terminals of the thirteenth and fourteenth transistors and the gate terminal of the fifteenth transistor, wherein the level shifted output signal is generated at the drain terminals of the fifteenth and sixteenth transistors.

10. The flip-flop circuit of claim 9, wherein the master stage includes:

a seventeenth transistor having a source terminal that receives the first supply voltage, and a gate terminal for receiving the input signal;

an eighteenth transistor having a source terminal connected to a drain terminal of the seventeenth transistor, and a gate terminal that receives the internal clock signal;

a nineteenth transistor having a drain terminal connected to a drain terminal of the eighteenth transistor, and a gate terminal that receives the inverted clock signal;

a twentieth transistor having a drain terminal connected to a source terminal of the nineteenth transistor, a gate terminal for receiving the input signal, and a source terminal connected to ground;

a second inverter having an input connected to the drain terminals of the eighteenth and nineteenth transistors;

a twenty-third transistor having a source terminal that receives the first supply voltage, and a gate terminal connected to an output of the second inverter;

a twenty-fourth transistor having a source terminal connected to a drain terminal of the twenty-third transistor, a gate terminal that receives the inverted clock signal, and a drain terminal connected to the input of the second inverter;

a twenty-fifth transistor having a drain terminal connected to the drain terminal of the twenty-fourth transistor, and a gate terminal that receives the internal clock signal;

a twenty-sixth transistor having a drain terminal connected to a source terminal of the twenty-fifth transistor, a gate terminal connected to the gate terminal of the twenty-third transistor and the output of the second inverter, and a source terminal connected to ground; and

a third inverter having an input connected to the output of the second inverter and to the gates of the twenty-third and twenty-sixth transistors, and an output that provides the master stage output signal.

11. The flip-flop circuit of claim 10, wherein the second inverter comprises:

a twenty-first transistor having a source terminal for receiving the first supply voltage, and a gate terminal connected to the drain terminals of the eighteenth and nineteenth transistors;

a twenty-second transistor having a drain terminal connected to a drain terminal of the twenty-first transistor, for generating the clocked input signal, a gate terminal connected to the gate terminal of the twenty-first transistor, and a source terminal connected to ground.

12. The flip-flop circuit of claim 11, wherein the third inverter comprises:

a twenty-seventh transistor having a source terminal that receives the first power supply voltage and a gate terminal connected to the drain terminals of the twenty-first and twenty-second transistors; and

a twenty-eighth transistor having a drain terminal connected to a drain terminal of the twenty-seventh transistor, a gate terminal connected to the drain terminals of the twenty-first and twenty-second transistors, and a source terminal connected to ground.

13. The flip-flop circuit of claim 10, wherein the master stage further comprises:

a fourth inverter having an input that receives the clock signal and an output that provides the inverted clock signal; and

a fifth inverter having an input connected to the output of the fourth inverter and an output that provides the internal clock signal.

14. The flip-flop circuit of claim 13, wherein the fourth inverter comprises:

a twenty-ninth transistor having a source terminal that receives the first supply voltage, a gate terminal for receiving the clock signal, and a drain terminal for generating the inverted clock signal; and

a thirtieth transistor having a drain terminal connected to the drain terminal of the twenty-ninth transistor, a gate terminal connected to the gate terminal of the twenty-ninth transistor, and a source terminal connected to ground; and

wherein the fifth inverter comprises;

a thirty-first transistor having a source terminal that receives the first supply voltage, a gate terminal connected to the drain terminals of the twenty-ninth and thirtieth transistors, for receiving the inverted clock signal, and a drain terminal for generating the internal clock signal; and

a thirty-second transistor having a drain terminal connected to the drain terminal of the thirty-first transistor, a gate terminal connected to the gate terminal of the thirty-first transistor, and a source terminal connected to ground.

15. The flip-flop circuit of claim 10, wherein the first, second, eighth, ninth, tenth, thirteenth, seventeenth, eighteenth, and twenty-third transistors are p-channel metal-oxide semiconductor (PMOS) transistors.

16. The flip-flop circuit of claim 10, wherein the third, fourth, fifth, sixth, seventh, eleventh, twelfth, fourteenth, nineteenth, twentieth, and twenty-sixth transistors are n-channel metal-oxide semiconductor (NMOS) transistors.

17. The flip-flop circuit of claim 8, wherein the second supply voltage is different from the first supply voltage.