AMPLITUDE CONTROL SYSTEM

PROBLEM TO BE SOLVED: To attain high speed and accurate amplitude switching regardless of its low cost. SOLUTION: Integration devices 32a, 32b in pairs connected in parallel are integrated in an automatic level control loop and switches S2, S3 are used to select either of the devices 32a, 32b. Since drive voltages 34a, 34b given to a level modulator 12 are stored in advance to each of the integration device pair in advance as initial values, settling of a system output signal 45 is disregarded, the amplitude of the test signal 50 is quickly and accurately switched so as to avoid a switching transient phenomenon. Even when a plurality of setting voltages are provided, one signal generator is enough and only the number of the integration devices connecting to the loop and the number of reference signals 40a, 40b corresponding to the setting voltages have only to be increased, then the circuit is realized easily at a low cost.