Motorola Corporation

Eugene Walton Hodges, Iii

Wayne W Ballantyne

Leng H Ooi

Francis Robert Steel

Ralph T Enderby

A frequency synthesizer circuit, having first and second modes of operation, comprises a voltage-controlled oscillator (VCO) (64), a low-pass filter (74), a phase-locked loop (PLL) (67), an analog-to-digital converter (50), a digital-to-analog converter (56), a controller (48), and a VCO input switch. During the first mode, the VCO input switch couples the control input of the VCO to a control signal produced by the PLL, and the analog-to-digital converter measures the control signal and provides it to the controller which stores the control voltage measured by the analog-to-digital converter. During the second mode, the VCO input switch couples the control input of the VCO to the digital-to-analog converter which applies the stored control to the control input of the VCO.

Frequency synthesizer with VCO output control

A non-reciprocal signal path for RF over a broadband frequency range is provided by an isolator comprising two coils or meshes positioned at 90.degree. to each other adjacent at least one gyromagnetic or ferrite disc which is magnetically biased by a static magnetic field. Each coil is tuned by a parallel capacitor, each coil and capacitor having one end grounded to a surrounding electromagnetic shield. A resistive unilateralizing element is coupled between the input and output terminals and, being essentially non-reactive, provides the broadband characteristic. The energy from the reverse direction is dissipated externally in the resistive element. A magnetic return path of a high permeability material allows the use of smaller biasing magnets and reduces the effects of external magnetic fields.

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Eugene Walton Hodges, Iii