A circuit for generating a common signal as a function of either of two reference signals comprises a pair of phase-locked loops which share an oscillator. Each phase-locked loop generates a control signal as a function of one of the reference signals. One or the other of the control signals is coupled to the oscillator which generates the common signal. A comparator compares the two control signals and generates a signal indicative of their difference. While the control signal generated by the first phase-locked loop is coupled to the oscillator, the difference signal is applied to the second phase-locked loop where it controls the generation of the second control signal to minimize the difference between the two control signals. While the control signal generated by the second phase-locked loop is coupled to the oscillator, the second phase-locked loop is nonresponsive to the difference signal. Thus when a switch of reference signals occurs even if they are of different phase and even if that phase is slowly time-varying, the circuit can lock to the new reference signal at a phase dictated by the phase difference between the two references at the instant of the switch without causing the oscillator output to undergo significant frequency or phase changes.

Apparatus for generating a common output signal as a function of any of a plurality of diverse input signals

Ultra-narrow-band system for communication between a transmitter device and a receiver device provided by locking both to a carrier signal from a radio broadcast station and synthesizing a precise local frequency at each device as a preset multiple of the frequency of the carrier. Such a system is usable in a multi-station alarm and status communication system including a multiplicity of independent radio alarm transmitters whose various carrier frequencies are different from but phased locked to a local radio broadcast station, and a central alarm receiving station which employs a corresponding multiplicity of synchronous detectors. The detectors each have associated with them a synthesized local oscillator source which is also phase-locked to the same radio broadcast station used by the alarm transmitters. Both the alarm transmitters and the central receiver are thereby accurately referenced to a readily available local frequency source (the broadcast station). As a consequence, very narrow-band radio circuits may be employed and the receiver and transmitter bandwidth may be accurately matched to the information content of the alarm and status signal source to achieve high signal-to-noise ratio reliable transmissions. The disclosed apparatus is relatively immune to intentional or unintentional interference and will burn-through most conventional transmissions which may be transmitting on the same radio channel at the same time, without unduly bothering those other unrelated transmissions.

Narrow-band radio communication system

A circuit design extending the range and linearizing the transfer characteristic of a fast voltage controlled oscillator (VCO). In addition, a multi-range VCO is described. Range extension is achieved by modifying the delay cell of a current controlled ring oscillator. The VCO transfer characteristic is linearized by piece-wise linear current control added to the delay cell. Additionally, a VCO capable of multi-range operation is provided. With the addition of multiple current sources which control booster inverter current, and by selectively enabling the additional current sources, a VCO with multiple frequency ranges can be achieved.

Multi-range voltage controlled oscillator

A voltage controlled oscillator (VCO) having a generally linear transfer characteristic across a wide frequency range of operation. The VCO is comprised of a voltage-to-current converter (V-I) and a current-controlled oscillator (ICO). A linearization of the output response of the VCO is accomplished by proper selection of the output responses of the V-I and ICO circuits, where the V-I portion is designed to have an inverse nonlinearity response as compared to the nonlinearity response of the ICO portion of the VCO. The combined effect is a linear response for the VCO. A nonlinear V-I characteristic can be achieved by adding several piecewise linear responses together to produce a combined nonlinear response.

Linearization method and apparatus for voltage controlled oscillator

Extendible-range voltage controlled oscillator

1,237,985. Frequency synthesizers. RCA CORPORATION. 10 Nov., 1969 [26 Nov., 1968], No. 54926/69. Heading H3A. A digital stabilized frequency synthesizer has two phase locked loops around the same controlled oscillator there being means in the first loop whereby phase of the oscillator is corrected at a rate which is the same or a submultiple of the channel spacing frequency and means in this loop to select the channel at which the synthesizer operates, and means in the second loop whereby the oscillator phase is corrected at a variable rate considerably higher than the channel spacing and always a submultiple of the synthesizer output frequency. Voltage controlled oscillator 1 is coupled by variable-ratio divider 22 to phase-discriminator 26 the second input of which is derived from reference oscillator 30 over fixed divider 32: the output of phase discriminator 26 controls the frequency of oscillator 1, via low-pass filter 36. For control of the short-term stability of oscillator 1, it is coupled in a second loop comprising variable ratio divider 40, ganged with divider 22 but only dividing by the first four significant figures set up in divider 22, phase discriminator 44 and high-pass filter 60. The second input of phase discriminator 52 is derived from crystal oscillator 46, whose frequency is controllable over a small range, and fixed divider 50. The output from phase discriminator 44 also controls the frequency of oscillator 46, via low-pass filter 56.

David H Westwood

Papers

Digital frequency synthesizer

Anti-hunt circuit for electric motor follow-up systems

Electric pulse delay circuit