PURPOSE: To attain the adjustment of free-run frequency and temperature compensation due to variance in manufacture of an integrated circuit by providing another control terminal at the outside of a PLL comprising a voltage controlled oscillator, a frequency divider, a phase comparator, a charge pump and an LPF.
CONSTITUTION: An output of the VCO2 is frequency-divided by the frequency divider 3 and the frequency dividing output and an external input signal 7 become inputs to the phase comparator 4. The charge pump 5 consists of a PCH MOS-TR31 and an NCH MOS-TR32, and when an external signal at a terminal 7 is faster than the signal frequency-dividing the oscillated frequency, the TR32 is turned on and when slower, the TR31 is turned on. In the figure, 6 is the LPF. In this case, the relation of fosc=f0×N is established, where fosc is the oscillated frequency, N is the frequency dividing ratio, and f0 is an external input frequency. Although it is necessary to stabilize the free-run frequency for the stable operation of the PLL, since a threshold voltage and an amplification factor or the like are changed depending on the manufacture conditions of the MOS-TRs and each parameter has each temperature characteristic, stable PLL conditions can not be maintained. In this invention, a gate of a PCH MOS-TR8 is controlled by resistors 11, 12 and a thermister 13 to stabilize the operation.
CHIHARA HIROYUKI
IKEJIRI HIROAKI
