Fujitsu Corporation

Kazuhiro Kitani

Kunihiko Gotoh

Yuji Segawa

Katsuaki Aizawa

Masatake Kusakari

A protection circuit in a semiconductor integrated circuit having a master slice I/O circuit comprises an internal circuit, a pad, and a desired number of protection elements connected in parallel between the internal circuit and the pad. Each protection element includes a P-channel MOS transistor which outputs a first power supply voltage level signal on the basis of an output signal of the internal circuit, a N-channel MOS transistor which outputs a second power supply voltage level signal on the basis of the output signal of the internal circuit, a resistor connected between a signal line connected to the pad and an output terminal of the P-channel MOS transistor, and a resistor connected between the signal line and an output terminal of the N-channel MOS transistor.

Semiconductor integrated circuit

A compander circuit includes first and second volume controllers, a comparator, a counter and a control part. The comparator compares a compared voltage with a rectified and smoothed signal of an input signal of the compander circuit or an output signal of the first volume controller receiving the input signal, the compared voltage being an output signal of the second volume controller. The counter executes a count operation on an output signal of the comparator in synchronism with a clock signal and controls gains of the first and second volume controllers on the basis of a counter value of the counter. The control part controls a frequency of the clock signal applied to the counter by a predetermined control signal.

Compander circuit

In a half-wave rectifier circuit for obtaining an DC voltage output depending on the level of an input signal through half-wave rectification of the input signal, an input voltage from which a DC component is removed by a capacitor is input to a switch circuit. This input voltage includes an offset voltage which is generated by use of the capacitor. The switch circuit outputs a half-wave rectified voltage to a smoothing circuit by switching the input voltage ON and OFF depending on the polarity of the input signal. Under the condition that an input voltage is controlled to OFF state, the switch circuit shows a high impedance viewed from the input side of the smoothing circuit. Therefore, an output voltage of the smoothing circuit is maintained when the switch circuit is in the OFF state. Thereby, the offset voltage generated by the capacitor is eliminated from the output voltage from the smoothing circuit.

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Kawasaki, Japan

Kazuhiro Kitani