Radio transmitter architecture comprising a PLL and a delta-sigma modulator
AssigneeCadence Design Systems Inc. of San Jose
InventorMartin Wilson
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Abstract
The transmitter circuit architecture is disclosed based on a phase lock loop architecture and which uses a delta-sigma modulator with 2 point modulation. In order to restrict the bandwidth of the PLL, subsidiary analogue modulation is employed, which requires aligning with the delta-sigma modulation. Alignment of the modulation is accomplished by correction of the sensitivity of the PLL voltage controlled oscillator to modulation by correlating residual modulation in the PLL with the modulated signal input. The action of the modulation correlator trims the modulation and the PLL bandwidth without disturbing the normal operation of the transmitter, and allows the use of modulation bandwidths greater than the PLL bandwidth.
Claims17
A transmitter circuit means comprising:
- a phase lock loop including a phase detector means, a summation means, and a voltage controlled oscillator arranged in series, and a controllable frequency divider arranged to feedback an output of the voltage controlled oscillator to an input of the phase detector;
- and
- a baseband modulation source arranged to generate a modulation signal corresponding to information to be transmitted;
- a modulation correlation circuit means arranged to receive said modulation signal and to correlate said signal with residual modulation in the phase lock loop to generate one or more modulation correction signals;
- a delta-sigma modulator means arranged to receive said modulation signal and generate a delta-sigma control signal therefrom;
- and
- a modulation amplitude scaling means arranged to receive the modulation signal and the modulation correction signals and to scale the amplitude of the modulation signal in response thereto;
- wherein the scaled modulation signal is applied to the phase lock loop at the summation means in order to modulate the voltage controlled oscillator to produce a modulated RF output signal;
- and
- the delta-sigma control signal is applied to the controllable frequency divider in order to control the divide ratio thereof whereby the controllable frequency divider acts to substantially remove the modulation from the modulated RF output signal at the input to the phase detector.
A method for generating a modulated RF output signal in a phase lock loop including a phase detector means, a summation means and a voltage controlled oscillator arranged in series and a controllable frequency divider arranged to feedback an output to the voltage controlled oscillator to an input of the phase detector, the method comprising the steps of:
- generating a modulation signal corresponding to information to be transmitted;
- and characterized by further comprising the steps of:
- generating a delta-sigma control signal from the modulation signal in a delta-sigma modulator;
- applying the modulation signal to the summation means to modulate the voltage controlled oscillator to produce the modulated RF output signal as the output of said oscillator;
- applying the delta-sigma control signal to the controllable frequency divider in order to control the frequency divide ratio thereof;
- frequency dividing the modulated RF output signal in the controllable frequency divider in accordance with the frequency divide ratio of the divider;
- correlating residual modulation in the phase lock loop with the modulation signal, the result of the correlation being used to generate a modulation correction signal;
- and
- scaling the modulation signal applied to the summation means in response to the modulation correction signal;
- wherein said step of frequency dividing substantially removes the modulation from the RF output signal at the input of the phase detector.
Dependencies are inferred from the claim text.