Phase locked loop circuit

A phase locked loop circuit comprising a phase detector circuit, a low pass filter circuit and a voltage-controlled oscillator circuit, said phase detector circuit supplying a detection output signal proportional to the phase difference of the input signal and the oscillation output signal of said voltage-controlled oscillator circuit to said low pass filter, the phase of the oscillation output signal of said voltage-controlled oscillator circuit being controlled by the output signal of said low pass filter circuit, in which:

• said phase detector circuit includes at least a first differential pair of transistors and a second differential pair of transistors cascade-connected with said first differential pair of transistors, the base of either one of said first differential pair of transistors being applied with one of said input signal and said oscillation output signal of said voltage-controlled oscillator circuit as two input signals and the base of either one of said second differential pair of transistors being applied with the other of said two input signals;
• said voltage-controlled oscillator circuit includes at least a timing capacitor and a constant current source connected to said timing capacitor, and has the frequency of its oscillation output signal determined by the capacitance of said timing capacitor and a current flowing through said constant current source;
• and
• the current flowing through said constant current source is determined by the resistance of a variable resistor for current-setting, and simultaneously the current flowing through said one transistor of said second differential pair of transistors cascade-connected to said first differential pair of transistors of said phase detector circuit is also determined by the resistance of said current setting resistor.

An integrated circuit for a phase locked loop circuit formed in a monolithic semiconductor chip comprising:

• a voltage controlled oscillator including emitter-coupled transistors serving as a multivibrator, first and second terminals for connecting an external timing capacitor, first and second transistors having collectors connected to the emitters of said emitter-coupled transistors respectively, and an emitter resistor connected between the emitter of each of said first and second transistors and ground, an oscillation output of the oscillator being derived from either collector of said emitter-coupled transistors;
• a phase detector responsive to the output of said oscillator and an input signal applied to a third terminal for generating a detected signal proportional to the phase difference between the input signal and the oscillation output, said phase detector comprising,
• a first differential pair of transistors one of which is applied with the input signal at its base, and
• a second differential pair of transistors cascade-connected to said first pair of transistors, one of which is applied with the oscillation output at its base, and the emitters of each pair of transistors being coupled, the detected signal being derived from the collector of the other of said first pair of transistors and applied to the collector of said first transistor of the oscillator through an external low pass filter;
• constant current adjusting means for commonly adjusting a base voltage applied to the base of the other of said second differential pair of transistors and a base voltage applied to the bases of said first and second transistors of the oscillator in a predetermined correlation, said adjusting means comprising a fourth terminal for connecting an external potentiometer to select a constant current for adjustment, and a transistor circuit responsive to the potentiometer to provide said base voltages proportional to the selected constant current at a predetermined ratio with each other, thereby constantly determining the values of a constant current flowing through said other transistor of the second pair of transistors and constant currents flowing through said first and second transistors of the oscillator in said predetermined correlation.