Abstract: A programmable frequency synthesizer is disclosed having most components implemented on a single large scale integration (LSI) chip, which facilitates rapid frequency acquisition. Provision is made by the present invention to configure the frequency synthesizer for use in either a receiver or a transmitter. In the transmitter mode, modulation cancelling allows modulation down to approximate DC. A serial programming protocol is provided to program the frequency synthesizer.

Abstract: A buffer is described which includes two gain stages which may be constructed of MOS devices, the first stage having a low noise characteristic and the second stage having a high current drive capability. The second stage is switched in circuit only when high current drive is needed so that the buffer otherwise exhibits the low noise characteristics of the first stage. A feedback network is also switched in circuit in a manner that maintains the buffer's loop gain substantially constant, whether or not the high current drive stage is in circuit.

Abstract: A low frequency oscillator of the astable type having good frequency stability, fast starting, good immunity to DC loading, and suitable for fabrication in integrated circuit form. First and second switching transistors of the astable multivibrator are cross-coupled by a coupling capacitor and a frequency determining crystal. Base drive to the respective switching transistors and charging current to the capacitor and crystal are provided by a pair of differential amplifiers which are referenced to a forward biased diode. The differential amplifiers are also connected to respective collector terminals of the switching transistors. The capacitor is of small value suitable for containment within an integrated circuit with the oscillator circuit. The differential amplifiers substantially increase the impedance levels in the oscillator and shift base drive to the switching transistors to minimize the effects of DC loading at the output terminals of the oscillator.

Abstract: A wide frequency range current-controlled oscillator (CCO) provides a digital output signal that is frequency controllable by an input control current. The CCO includes a differential voltage comparator coupled to a timing capacitor for controlling charging and discharging currents applied to the timing capacitor. The charging and discharging currents are dependent on the input control current. The magnitude of the discharging current may be varied to control the duty cycle of the digital output signal.