Prepositioned frequency synthesizer and method therefor
AssigneeGeneral Dynamics Decision Systems, Inc.
InventorBruce Alan Fette
Life of this patent
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Abstract
A PLL-type frequency synthesizer (10) in which a loop filter (24) state is recorded during an earlier hop to a given frequency then assigned back to the loop filter (24) during a subsequent hop to the same frequency is disclosed. The state is recorded through an A/D converter (48) and assigned through a D/A converter (60). Offset and linearity error is compensated in a compensation circuit (54) so that the state subsequently assigned to the loop filter (24) accurately matches the state that was previously measured for recording. Reference frequency and output signal dividers (16, 40) are both immediately initialized at a hop boundary (82) so that the signals compared by a phase comparator (20) are forced into a phase-matched condition.
Claims21
A prepositioned frequency synthesizer for rapidly settling at new frequencies, said prepositioned synthesizer comprising:
- a first frequency divider configured to divide a frequency of a synthesizer-output signal by a number N;
- a second frequency divider configured to divide a frequency of a reference signal by a number M;
- a phase comparator having inputs coupled to said first and second frequency dividers;
- a loop filter coupled to said phase comparator;
- a variable frequency oscillator having an input coupled to said loop filter and an output configured to provide said synthesizer-output signal;
- a filter-state-recording circuit coupled to said loop filter and configured to record states exhibited by said loop filter;
- a filter-state-assigning circuit coupled to said loop filter and configured to assign states to said loop filter;
- and
- a controller coupled to said first and second dividers and to said filter-state-assigning circuit, said controller being configured to set said first and second frequency dividers to initial conditions and to assign a state to said loop filter when changing to a new frequency.
A prepositioned frequency synthesizer for rapidly settling at new frequencies, said prepositioned synthesizer comprising:
- a frequency divider configured to divide a frequency of a synthesizer-output signal by a number N;
- a reference frequency source;
- a phase comparator having a first input coupled to said frequency divider and a second input coupled to said reference frequency source;
- a loop filter coupled to said phase comparator;
- a variable frequency oscillator having an input coupled to said loop filter and an output configured to provide said synthesizer-output signal;
- a filter-state-recording circuit coupled to said loop filter and configured to record states exhibited by said loop filter;
- a filter-state-assigning circuit coupled to said loop filter and configured to assign states to said loop filter;
- and
- a compensation circuit coupled to said filter-state-recording circuit and to said filter-state-assigning circuit, said compensation circuit being configured to compensate for response differences between said filter-state-recording circuit and said filter-state-assigning circuit.
A method of operating a prepositioned frequency synthesizer to rapidly settle at a selected frequency, said method comprising:
- producing measured states by measuring actual states of a loop filter as said synthesizer outputs a plurality of discrete synthesizer-output frequencies, wherein said selected frequency is one of said plurality of discrete synthesizer-output frequencies;
- compensating said one of said measured states which corresponds to said selected frequency to generate an assigned state;
- assigning said assigned state to said loop filter, said assigned state being configured so that said loop filter exhibits substantially said actual state for said selected frequency after said assigning activity;
- initializing a synthesizer-output signal frequency divider to an initial state;
- initializing a reference signal frequency divider to an initial state;
- and
- programming said frequency dividers to divide by values that cause said synthesizer to generate said selected frequency.
Dependencies are inferred from the claim text.