Frequency synthesizer and related method for generating wideband signals
View Patent ↗A frequency synthesizer includes a phase-locked loop circuit having an output. A frequency divider is connected to the output of the phase-locked loop circuit for receiving the signal therefrom and dividing the frequency of the signal. A tunable bandpass filter is connected to the frequency divider and is tuned for selecting a harmonic frequency to obtain a fractional frequency division for a signal output from the phase-locked loop circuit.
1. A frequency synthesizer, comprising:
a signal reference circuit that generates a signal reference;
a first phase-locked loop circuit path connected to said signal reference circuit and comprising,
a first phase-locked loop circuit comprising a phase detector and a voltage controlled oscillator connected thereto and a feedback loop extending from the voltage controlled oscillator to the phase detector and a frequency divider positioned within the feedback loop, and a phase-locked loop output at the voltage controlled oscillator through which an RF signal is generated at a first frequency;
an integer frequency divider connected to the phase-locked loop output and operative to receive the signal therefrom and to divide the first frequency of the signal output from the first phase-locked loop circuit by an integer number;
a tunable bandpass filter connected to said integer frequency divider that is tuned for selecting a harmonic frequency to obtain a fractional frequency division to produce a local oscillator signal used for a first frequency specific digital television application;
a second phase-locked loop circuit path connected to said signal reference and comprising,
a second phase-locked loop circuit having an output;
a direct digital synthesizer connected to said second phase-locked loop circuit;
a mixer connected to said direct digital synthesizer and receiving a digital television service signal for mixing with signals for said direct digital synthesizer and producing a local oscillator signal used for a second frequency specific digital television application; and
a television signal frequency divider that receives the digital television service signal and generates a plurality of digital television service signals of different frequencies, and a switch connected between the mixer and frequency divider for selecting a desired frequency to be mixed with signals from the direct digital synthesizer.
2. The frequency synthesizer according to claim 1 , which further comprises a switch connected between the mixer and direct digital synthesizer for bypassing the mixer for analog television service.
3. The frequency synthesizer according to claim 1 , wherein said tunable bandpass filter is operative for removing a fundamental frequency and leaving the rest intact.
4. The frequency synthesizer according to claim 1 , wherein said frequency divider is operative for dividing the frequency output from the phase-locked loop circuit by an integer number such that after selection of the harmonic frequency by said tunable bandpass filter a fractional division is accomplished.
5. The frequency synthesizer according to claim 1 , wherein said tunable bandpass filter comprises a plurality of serially connected and tunable bandpass filters.
6. The frequency synthesizer according to claim 5 , and further comprising a bandpass filter select circuit operatively connected to each of said tunable bandpass filters for controlling said bandpass filters for tuning the bandpass filter to a fundamental harmonic frequency.
7. The frequency synthesizer according to claim 1 , and further comprising a variable attenuator connected to said tunable bandpass filter.
8. The frequency synthesizer according to claim 7 , wherein said variable attenuator comprises a filter circuit operable with said tunable bandpass filter for shaping said signal.