Test tone generator and method therefor

A test tone generator for a receiver that comprises a local oscillator (LO), the test tone generator comprising:

• an input arranged to receive an LO input signal;
• a dual-modulus divider circuit arranged to receive the LO input signal and generate a tone therefrom in a series of pulses at an offset frequency from the LO input signal;
• a modulation control circuit connected to an output of the dual-modulus divider circuit and arranged to provide a modulation control signal to the dual-modulus divider circuit;
• a tone shaping circuit having an input connected to the output of the dual-modulus divider circuit or an output of the modulation control circuit and arranged to convert the series of pulses into an output test tone;
• and
• an output connected to an output of the tone shaping circuit;
• and
• wherein the dual-modulus divider circuit and tone shaping circuit in combination are arranged to generate a test tone from the series of pulses at an offset frequency from the LO input signal, that does not contain frequency content at an image frequency.

A method for test tone generation for testing a receiver, the method comprising:

• receiving a local oscillator (LO) input signal at by a dual-modulus divider circuit in a test tone generator;
• generating a series of pulses at an offset frequency from the LO input signal by the dual-modulus divider circuit;
• counting a number of the pulses using at least one counter and resetting the dual-modulus divider circuit when a count threshold is reached;
• converting the series of pulses into an output test tone at an offset frequency from the LO input signal wherein the offset frequency is equal to a receiver image frequency under test, that does not contain frequency content at a desired receiver frequency or at other image frequencies that are not under test, by a tone shaping circuit connected to an output of the dual-modulus divider circuit;
• and
• outputting the output test tone to the receiver.

A wireless communication unit comprising:

• a test tone generator circuit an input arranged to receive a local oscillator (LO) input signal;
• a dual-modulus divider circuit arranged to receive the LO input signal and generate a tone therefrom in a series of pulses at an offset frequency from the LO input signal;
• a modulation control circuit connected to an output of the dual-modulus divider circuit and arranged to provide a modulation control signal to the dual-modulus divider circuit;
• a tone shaping circuit having an input connected to the output of the dual-modulus divider circuit or an output of the modulation control circuit and arranged to convert the series of pulses into an output test tone;
• and
• an output connected to an output of the tone shaping circuit;
• and
• wherein the dual-modulus divider circuit and tone shaping circuit in combination are arranged to generate a test tone from the series of pulses at an offset frequency from the LO input signal, that does not contain frequency content at an image frequency.