<p>Only a portion of a parallel circuit (27) of a frequency control circuit (11) is externally attached. Thus, a charge time t1 depends on the element characteristic of a circuit element arranged in a package of a semiconductor device (70) and affected by fabrication irregularities of the semiconductor device (70) while a discharge time t2 depends on the parallel circuit (27) externally attached to the semiconductor device (70). The parallel circuit (27) having appropriate element characteristic can be selected after fabrication of the semiconductor device (70). A circuit constant of each circuit is set so that the discharge time t2 depending on the element characteristic of the externally attached parallel circuit (27) is longer than the charge time t1 depending on the element characteristic of an internal circuit of the semiconductor device (70).</p>
