Switch element driver circuit and semiconductor device
Noise generation is reduced further. Oscillation control circuit 11 generates a modulation signal modulating oscillation frequency of an oscillation signal generated by oscillation circuit 12 and outputs modulation signal to same. Preferably, the modulation signal fluctuates period of the oscillation signal sequentially. The oscillation circuit 12 is composed of a ring oscillator, for example, and the power supply voltage or power supply current of the ring oscillator is controlled to fluctuate sequentially by the modulation signal output from the oscillation circuit 11. Buffer 14 of charge pump circuit 13 generates signals /Φ and Φ by the oscillation signal and drives capacitors C 1 and C 2 for supplying a higher voltage than the voltage of the power supply Vcc to gate of N-channel MOSFET Q 1.
1. A switch element driver circuit, comprising:
a charge pump circuit that generates a voltage supplied to a control end of a switch element;
an oscillation circuit that outputs a driving signal to operate said charge pump circuit to said charge pump circuit; and
an oscillation control circuit that controls said oscillation circuit to fluctuate period of said driving signal sequentially.
2. The switch element driver circuit as defined in claim 1 , wherein said oscillation control circuit generates a modulation signal to modulate an oscillation frequency of said oscillation circuit and output to said oscillation circuit.
3. The switch element driver circuit as defined in claim 2 , wherein said oscillation control circuit generates one of a triangle wave signal, a sine wave signal, a sawtooth wave signal, a random signal, a pseudo-random signal and a combination signal of these signals as said modulation signal.
4. The switch element driver circuit as defined in claim 1 , wherein said oscillation circuit comprises a ring oscillator having multistage-connected inverter circuits and at least one of voltage and current of a power supply of at least a part of said multistage-connected inverter circuits is controlled to fluctuate by said oscillation control circuit.
5. A semiconductor device comprising said switch element driver circuit as defined in claim 1 .
6. The semiconductor device as defined in claim 5 , further comprising said switch element.
7. The semiconductor device as defined in claim 6 , wherein said switch element is composed of an NMOS transistor that functions as a high-side switch.