State retention within a data processing system
View Patent ↗Power consumption may be reduced through the use of power gating in which power is removed from circuit blocks or portions of circuit blocks in order to reduce leakage current. One embodiment uses a modified state retention flip-flop capable of retaining state when power is removed or partially removed from the circuit. Another embodiment uses a modified state retention buffer capable of retaining state when power is removed or partially removed from the circuit. The state retention flip-flop and buffer may be used to allow for state retention while still reducing leakage current. Also disclosed are various methods of reducing power and retaining state using, for example, the state retention flip-flops and buffers. For example, software, hardware, or a combination of software and hardware methods may be used to enter a deep sleep or idle mode while retaining state.
1. A circuit comprising:
a first power domain including circuitry coupled to receive a first power supply signal; and
a second power domain including circuitry coupled to receive both the first power supply signal and a second power supply signal, the second power domain including a buffer, the buffer comprising:
a first buffer portion coupled to receive the second power supply signal, the first buffer portion including a buffer data input; and
a second buffer portion coupled to receive the first power supply signal, the second buffer portion including a buffer data output, wherein one of the first and second power supply signals is configured to be selectively enabled independently from the other of the first and second power supply signals;
wherein:
each of the first and second buffer portions includes a data path portion coupled in series between the buffer data input and the buffer data output;
the second buffer portion includes a feedback portion which is coupled to receive a power gate indicator to enable the feedback portion during a power saving mode; and
the data path portion of the first buffer portion is an inverter which is disabled by the power gate indicator during the power saving mode.
2. The circuit of claim 1 further comprising a gate circuit coupled to receive the first power supply signal and to selectively provide the second power supply signal.
3. The circuit of claim 1 wherein the first power supply signal is provided to the circuit substantially continuously during operation of the circuit and the second power supply signal is derived from the first power supply signal and is provided to the circuit during a non-power saving mode of operation.
4. The circuit of claim 3 wherein the first and second power supply signals are designed to have substantially similar voltages during non-power saving operation.
5. The circuit of claim 1 further comprising a memory, wherein the buffer input is coupled to receive an output signal from the memory.
6. The circuit of claim 1 , wherein the feedback portion is disabled during normal operation.
7. A circuit comprising:
a first power domain including circuitry coupled to receive a first power supply signal; and
a second power domain including circuitry coupled to receive both the first power supply signal and a second power supply signal, the second power domain including a buffer, the buffer comprising:
a first buffer portion coupled to receive the second power supply signal, the first buffer portion including a buffer data input; and
a second buffer portion coupled to receive the first power supply signal, the second buffer portion including a buffer data output, wherein one of the first and second power supply signals is configured to be selectively enabled independently from the other of the first and second power supply signals;
wherein:
the first buffer portion comprises a first data path inverter having a data input coupled to the buffer data input, a data output coupled to the second buffer portion, and an enable control input;
the second buffer portion comprises:
a second data path inverter having a data input coupled to the output of the first inverter and a data output coupled to the buffer data output;
a feedback inverter having a data input coupled to the buffer data output, a data output coupled to the data input of the second inverter, and an enable control input, wherein each of the enable control inputs of the first data path inverter and the feedback inverter are coupled to receive a power gating control signal to alternately enable one of the first data path inverter and the feedback inverter while disabling the other of the first data path inverter and the feedback inverter.
8. The circuit of claim 1 , wherein the feedback portion is disable during normal operation.
9. A circuit comprising:
a gate circuit coupled to receive and gate a first power supply signal to controllably provide a second power supply signal;
a plurality of buffer cells, each buffer cell comprising:
a buffer input;
a buffer output;
an inverter having an inverter input coupled to the buffer input, the inverter being coupled to receive the second power supply signal, the inverter having an inverter output; and
a latch having a latch input coupled to the inverter output and a latch output coupled to the buffer output, the latch being coupled to receive the first power supply signal, and wherein, during normal operation, at least a portion of the latch is disabled and only a single inverter output of the latch is coupled to the buffer output.
10. The circuit of claim 9 further comprising:
a state retention controller coupled to provide a power control signal to the gate circuit, the gate circuit coupling the first power supply signal to the second power supply signal such that the first and second power supply signals have a substantially equal potential responsive to the power control signal having a first value, the gate circuit decoupling the first power supply signal from the second power supply signal to disable circuitry powered by the second power supply signal responsive to the power control signal having a second value.
11. The circuit of claim 10 wherein the state retention controller is coupled to receive a power gate request signal, the power gate request signal initiating a first mode of operation of the circuit with a first power gate request value, the power gate request signal initiating a second mode of operation of the circuit with a second power gate request value, the second mode of operation of the circuit being designed to consume less power than the first mode of operation of the circuit.
12. A circuit comprising:
a first power domain including circuitry coupled to receive a first power supply signal; and
a second power domain including circuitry coupled to receive both the first power supply signal and a second power supply signal, the second power domain including a buffer, the buffer comprising:
a first buffer portion coupled to receive the second power supply signal, the first buffer portion including a buffer data input; and
a second buffer portion coupled to receive the first power supply signal, the second buffer portion including a buffer data output, wherein one of the first and second power supply signals is configured to be selectively enabled independently from the other of the first and second power supply signals;
wherein:
the first buffer portion comprises a first data path inverter; and
the second buffer portion comprises a second data path inverter having a data input coupled to a data output of the first data path inverter, the second buffer portion further comprising state setting circuitry for setting a state of the buffer responsive to receiving a state retention signal at a state retention data input, wherein the state retention signal represents one of a desired logic value of the state of the buffer or an inverse of the desired value of the state of the buffer.
13. The circuit of claim 12 wherein the state retention signal is disabled when a power gate indicator signal has a first value indicating a non-power saving mode of operation for the buffer.
14. The circuit of claim 12 wherein the state retention signal is programmable.
15. The circuit of claim 12 wherein the state retention signal is hardwired to a particular logic value.
16. The circuit of claim 12 wherein the first data path inverter is coupled to receive a power gate indicator signal at a control input; and
the state setting circuitry comprises an inverter coupled to receive the state retention signal at a state retention data input and coupled to receive an inverted power gate indicator signal at an state retention control input.
17. The circuit of claim 12 wherein the state setting circuitry comprises:
a transistor having a first current handling terminal coupled to the data input of the second data path inverter, a second current handling terminal coupled to receive the state retention signal, the state retention signal being a power supply signal, and a control terminal coupled to be controlled according to a power gate indicator signal.
18. The circuit of claim 17 wherein the first data path inverter is coupled to receive the power gate indicator signal at an enable input;
the transistor is a pull-down transistor having a control terminal coupled to receive the power gate indicator signal; and
the power supply signal is coupled to a ground potential.
19. The circuit of claim 17 wherein the first data path inverter is coupled to receive the power gate indicator signal at an enable input;
the transistor is a pull-up transistor having a control terminal coupled to receive an inverted power gate indicator signal; and
the power supply signal is coupled to VDD.
20. A circuit comprising:
a first power domain including circuitry coupled to receive a first power supply signal; and
a second power domain including circuitry coupled to receive both the first power supply signal and a second power supply signal, the second power domain including a buffer, the buffer comprising:
a first buffer portion coupled to receive the second power supply signal, the first buffer portion including a buffer data input; and
a second buffer portion coupled to receive the first power supply signal, the second buffer portion including a buffer data output, wherein one of the first and second power supply signals is configured to be selectively enabled independently from the other of the first and second power supply signals;
wherein:
each of the first and second buffer portions includes a data path portion coupled in series between the buffer data input and the buffer data output;
the data path portion of the first buffer portion is an inverter and the data path portion of the second buffer portion comprises at least a portion of a latch; and
only a single inverter output of the second data path portion provides the buffer data output.