Cisco Systems Wireless Networking (Australia) Pty Limited

Cisco Technology, Inc.

Stephen C Avery

Andrew Robert Adams

Neil Weste

A frequency synthesizer, a calibrator thereof, and an operating controller thereof are described. The synthesizer comprises a main charge pump that drives a voltage controlled oscillator (VCO) through a loop filter. The calibrator includes a second, replica charge pump that can also drive the VCO, but is set up to output only its maximum or minimum analog output control voltage. Since the construction and characteristics of the replica charge pump duplicate the main charge pump, the main charge pump's minimum and maximum analog control outputs can be cloned out to the VCO on demand. A VCO calibration procedure therefore includes switching the VCO to each of its ranges set by a bank of fixed capacitors, and using the replica charge pump to drive the VCO to its minimum and maximum frequency for each range setting. The min-max frequency data is stored in a lookup table, and operational requests to switch to a new channel frequency can be supported with a priori information about which fixed-capacitor range selection will be best. The operating point controller includes a sensor to sense the operating point and a controller that provides a switching input to a switchable bank of capacitors to change the operating point. The change can be determined according to calibration data.

Frequency synthesizer using a VCO having a controllable operating point, and calibration and tuning thereof

A phase locked loop (PLL) frequency synthesizer includes a voltage controlled oscillator (VCO) to provide a VCO frequency signal, a frequency offset circuit including a mixer accepting the VCO frequency signal and a signal from a second oscillator to produce a shifted-frequency signal having a frequency significantly lower than the VCO output frequency, a programmable divider accepting the shifted-frequency signal and dividing the frequency of the shifted-frequency signal by a settable amount, a phase detector to compare the phase of the output of the programmable divider to that of a reference oscillator and produce a phase difference signal; and a loop filter to filter a function of the phase difference to produce a control input to the VCO. The offset circuit shifts down the frequency without increasing the divide ratio of the loop as would a prescaler achieving the same frequency conversion as the frequency offset circuit.

Offset mode phase locked loop frequency synthesizer with reduced divide ratio

A local oscillator calibrator comprises a main charge pump that drives a voltage controlled oscillator (VCO) through a loop filter. A second, replica charge pump can also drive the VCO, but is setup to output only its most positive or most negative analog output control voltage. Since the construction and characteristics of the replica charge pump duplicate the main charge pump, the main charge pump's minimum and maximum analog control outputs can be cloned out to the VCO on demand. A VCO calibration procedure therefore includes switching the VCO to each of its ranges set by a bank of fixed capacitors, and using the replica charge pump to drive the VCO to its minimum and maximum frequency for each range setting. The min-max frequency data is stored in a lookup table, and operational requests to switch to a new channel frequency can be supported with a priori information about which fixed-capacitor range selection will be best.

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Kellyville, Australia

Stephen C Avery