Abstract A PLL frequency synthesizer comprises a reference oscillator (1, 2), a frequency divider (8), a phase comparator (3) for phase-comparing the output of the reference oscillator (1, 2) with the output of the frequency divider (8), and first and second loop filters (5 and 13, resp.) coupled to the output of the phase comparator (3). First and second level holders (19 and 20, resp.) hold the output levels of the first and second loop filters (5 and 13, resp.) in response to first and second control signals, respectively (A and B, resp.) and first and second voltage controlled oscillators (6 and 14, resp.) vary oscillation frequencies in response to the outputs of the first and second level holders, respectively. Switch means (23) selectively supply the output signals of the first and second voltage controlled oscillators (6 and 14, resp.) to the input of the frequency divider (8) in response to a third control signal. Such a transmit receive PLL frequency synthesizer has a small circuit scale and consumes a minimum of power (Fig. 2).
A PLL frequency synthesizer comprising: reference oscillation circuit means; frequency divider circuit means; phase comparator means for phase-comparing the output of said reference oscillator means with the output of said frequency divider circuit means; first and second loop filter means coupled to the output of said phase comparator means; first and second level holder means for holding the output levels of said first and second loop filter means in response to first and second control signals, respectively; first and second voltage controlled oscillator.means for varying oscillation frequencies in response to the outputs of said first and second level holder means, respectively; and switch means for selectively supplying the output signals of said first and second voltage controlled oscillator means to the input of said frequency divider circuit means in response to a third control signal.
Claim 2
Dependent Claim
135 words
A PLL frequency synthesizer comprising: reference oscillation circuit means; frequency divider circuit means; phase comparator means for phase-comparing the output of said reference oscillator means with the output of said frequency divider circuit means; first and second loop filter means coupled to the output of said phase comparator means; first and second level holder means for holding the output levels of said first and second loop filter means in response to first and second control signals, respectively; first and second voltage controlled oscillator.means for varying oscillation frequencies in response to the outputs of said first and second level holder means, respectively; and switch means for selectively supplying the output signals of said first and second voltage controlled oscillator means to the input of said frequency divider circuit means in response to a third control signal.
Claim 3
Dependent Claim
32 words
A PLL frequency synthesizer as claimed in claim 1, wherein said reference oscillation circuit means comprises a reference oscillator and a reference frequency divider for frequency-dividing the output of said reference oscillator.
Claim 4
Dependent Claim
46 words
A PLL frequency synthesizer as claimed in claim 1 or 2, wherein said frequency divider circuit means comprises a prescaler connected to the output of said switch means, and a programmable frequency divider responsive to a fourth control signal for frequency-dividing the output of said prescaler.
Claim 5
Dependent Claim
43 words
A PLL frequency synthesizer as claimed in any of claims 1 to 3, further comprising first and second charge pump circuit means provided between the output of said phase comparator means, and the inputs of said first and second loop filter means, respectively.
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