Multi-oscillator circuit with variable power supply
View Patent ↗This invention makes it possible to reduce a power consumption of an electronic circuit (microcomputer, for example) while preventing malfunctioning of an oscillator by appropriately setting a power supply impedance of a low frequency oscillator corresponding to an operation mode. A high frequency oscillator, a medium frequency oscillator and a low frequency oscillator are provided as sources of system clocks. In addition, there is provided a quartz oscillator to generate a clock for a timepiece. When the high frequency oscillator is in operation, a power supply impedance of the quartz oscillator is reduced to improve a noise tolerance. In a waiting period during which the high frequency oscillator, the medium frequency oscillator and the low frequency oscillator are halted, on the other hand, the power supply impedance of the quartz oscillator is increased to suppress the power consumption.
1. An electronic circuit comprising:
a first oscillator generating a first clock, a power supply impedance of the first oscillator being configured to be variable and controllable;
a second oscillator generating a second clock, a frequency of the second clock being higher than a frequency of the first clock;
a third oscillator generating a third clock, a frequency of the third clock being higher than the frequency of the second clock; and
a control circuit setting the power supply impedance of the first oscillation circuit to a high impedance when the second and the third oscillators are halted, setting the power supply impedance of the first oscillator to a medium impedance when the second oscillator is in operation and the third oscillator is halted, and setting the power supply impedance of the first oscillator to a low impedance when the third oscillator is in operation and the second oscillator is halted.
2. The electronic circuit of claim 1 , wherein the control circuit comprises a register to store a control signal to control the power supply impedance of the first oscillator and controls the power supply impedance of the first oscillator based on the control signal stored in the register.
3. The electronic circuit of claim 2 , further comprising an operation mode switching circuit that outputs an operation mode switching signal to put the second oscillator or the third oscillator into operation, wherein the control circuit controls the power supply impedance of the first oscillator based on the operation mode switching signal.
4. The electronic circuit of claim 1 , further comprising an operation mode switching circuit that outputs an operation mode switching signal to put the second oscillator or the third oscillator into operation, wherein the control circuit controls the power supply impedance of the first oscillator based on the operation mode switching signal.
5. The electronic circuit of claim 1 , wherein the first oscillator comprises a quartz oscillator.
6. The electronic circuit of claim 5 , wherein the first oscillator comprises a first terminal, a second terminal, a quartz resonator and an amplifier connected between the first terminal and the second terminal, a power supply line to provide the amplifier with a power supply electric potential, a ground line to provide the amplifier with a ground electric potential, and a power supply impedance switching unit comprising switching devices to vary the power supply impedance and disposed between the power supply line and a power supply terminal of the amplifier or between the ground line and a ground terminal of the amplifier, the switching devices in the power supply impedance switching unit being turned on or off by the control circuit.
7. The electronic circuit of claim 1 , wherein the second oscillator comprises an RC oscillator or a ceramic filter oscillator.