Double-conversion television tuner using a Delta-Sigma Fractional-N PLL

A double-conversion tuner, comprising:

• an input for receiving an RF signal having a number of channels;
• a first mixer configured to up-convert said RF signal to a first IF signal using a first local oscillator signal;
• a first local oscillator having a delta-sigma fractional-N phase lock loop to produce said first local oscillator signal, said delta-sigma fractional-N phase lock loop configured to perform fine tuning of said first local oscillator signal and configured to have a wide tuning range sufficient to cover said number of channels, and said delta-sigma fractional-N phase lock loop including
• a feedback path having a programmable frequency divider, and
• a delta-sigma modulator configured to receive a static fractional input and generate an output having a plurality of pulses that when averaged over time have an amplitude corresponding to said static fractional input, said delta-sigma modulator including
• an input multiplier at an input to said delta-sigma modulator, said input multiplier configured to multiply said static fractional input by a coefficient,
• a series of stages, each stage including
• a first summer,
• a second summer,
• a register, and
• a stage multiplier, and
• a slicer configured to quantize an output of a last register of a last stage of said series of stages so as to produce an integer at an output of said slicer,
• wherein said stage multiplier is configured to multiply an output of said slicer by a coefficient, output of said stage multiplier coupled to an input of said first summer, output of said first summer coupled to an input of said second summer, output of said second summer coupled to an input of said register, output of said register coupled to said input of said first summer and an input of a subsequent stage, and output of said input multiplier coupled to an input of a first stage of said series of stages;
• a bandpass filter configured to select a subset of channels from said first IF signal;
• a second mixer configured to down-convert said subset of channels to a second IF signal using a second local oscillator signal;
• and
• a second local oscillator configured to generate said second local oscillator signal, and configured to perform coarse frequency tuning and have a narrow tuning range relative to said first local oscillator.

A method of receiving an RF signal, the method comprising the steps of:

• (a) receiving an input RF signal having a number of channels;
• (b) generating a first local oscillator signal;
• (c) fine-tuning said first local oscillator signal, said fine-tuning including:
• (i) receiving a reference signal and a static fractional input,
• (ii) modulating said reference signal with said static fractional input to generate an averaged output having a plurality of pulses that when averaged over time have an amplitude corresponding to said static fractional input, said modulating step including
• processing said reference signal and said static fractional input through a series of alternating summers and registers,
• quantizing the result of the processing step to produce said averaged output, and
• multiplying said averaged output by a plurality of coefficients,
• (iii) summing said averaged output with a value,
• (iv) dividing the frequency of said first local oscillator signal by said summed output of step (iii), and
• (v) comparing said divided first local oscillator signal with said reference signal;
• (d) up-converting said input RF signal to a first IF signal using said first local oscillator signal;
• (e) filtering said first IF signal to select a subset of channels from said first IF signal;
• (f) generating a second local oscillator signal;
• (g) coarsely-tuning said second local oscillator signal relative to said fine-tuning of step (c);
• and
• (h) down-converting said subset of channels to a second IF signal using said second local oscillator signal.

A method of receiving an RF signal, the method comprising the steps of:

• receiving an input RF signal having a number of channels;
• up-converting said input RF signal to a first IF signal using a first local oscillator signal;
• filtering said first IF signal to determine a selected channel from said first IF signal;
• down-converting said selected channel to a second IF signal using a second local oscillator signal;
• and
• fine tuning said selected channel by adjusting said first local oscillator signal, and coarse tuning said selected channel by adjusting said second local oscillator signal,
• said fine-tuning step including:
• (i) receiving a reference signal and a static fractional input,
• (ii) modulating said reference signal with said static fractional input to generate an averaged output having a plurality of pulses that when averaged over time have an amplitude corresponding to said static fractional input, said modulating step including
• processing said reference signal and said static fractional input through a series of alternating summers and registers,
• quantizing the result of the processing step to produce said averaged output, and
• multiplying said averaged output by a plurality of coefficients,
• (iii) summing said averaged output with a value,
• (iv) dividing the frequency of said first local oscillator signal by said summed output of step (iii), and
• (v) comparing said divided first local oscillator signal with said reference signal.