Phase locked loop (PLL) circuit having enhanced frequency select

Details Phase locked loop (PLL) circuit having enhanced frequency select Phase locked loop (PLL) circuit having enhanced frequency select

1990-11-30

1993-02-09

Pascal, Robert J.

Oscillators

Automatic frequency stabilization using a phase or frequency...

With reference oscillator or source

331111, 331177R, H03L 700

Patent

active

051855844

ABSTRACT:
A phase locked loop (PLL) circuit comprises a phase comparator, a low-pass filter, an error amplifier, and a voltage controlled oscillator (VCO) circuit which includes a current mirror circuit section and oscillator circuit section to provide an oscillation frequency based on the output current of the current mirror circuit section. To vary the oscillation over a wide range, a fixed reference voltage circuit is connected to the current mirror circuit, and either a source follower circuit made of a MOSFET or a FET or an emitter follower circuit made of a bipolar transistor is included is also connected to the current mirror circuit to selectively varying the output current of the current mirror circuit section upon application of a control voltage applied to the follower circuit. Thus, the follower circuit is controlled by a control voltage while the output current of the current mirror circuit varies depending on the magnitude of the control voltage, and, in turn, the oscillating frequency of the oscillator circuit section varies over a wide frequency range, e.g., in excess of 100 dB, in accordance with the output current.

REFERENCES:
patent: 3610954 (1970-10-01), Treadway
patent: 4975662 (1990-12-01), Takeuchi

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