ENVELOPE DETECTION CIRCUIT

PURPOSE:To eliminate the need of changing circuit parts in accordance with a change in an AC component contained in input signals by successively converting the input signals into digital signals and, only when the input signals largely change, converting the digital signals into analog signals. CONSTITUTION:When signals are inputted from a terminal 1, an A/D converter 10 performs A/D conversion in accordance with a clock signal 14 and outputs the converted digital signals from terminals D0-D5. The higher-rank four bits of the digital signals are inputted to the terminals A0-A3 of a comparator 12 and, at the same time, to the terminals D0-D3 of the first latch 11. Upon receiving the next clock, the latch 11 outputs data to the terminals B0-B3 of the comparator 12. Therefore, the comparator 12 compares the data of the terminals A0-A3 with the preceding data of the terminals B0-B3. When both data are different from each other, the higher-rank four bits of the digital signals are different, namely, the input signals largely change. In such case, the data of the second latch 16 are converted into analog signals by means of a D/A converter 17.