Method and circuit for producing a reference frequency signal using a reference frequency doubler having frequency selection controls

An integrated circuit (IC), comprising:

• a reference frequency generator input for generating a first reference frequency, a frequency doubler connected to the input, and an output;
• and
• a phase locked loop (PLL);
• the frequency doubler including:
• a delay circuit coupled to the input;
• an XOR circuit having a first input coupled to an output of the delay circuit and a second input coupled to the input;
• and
• an output of the first XOR circuit coupled to the input the PLL including:
• a frequency phase detector having a first input coupled to the output of the reference frequency generator;
• a filter having an input coupled to an output of the frequency phase detector;
• a voltage-controlled oscillator (VCO) having an input coupled to an output of the filter;
• a divider having an input coupled to an output of the VCO and an output coupled to a second input of the frequency phase detector;
• and
• the delay circuit including:
• a first delay element coupled to the input;
• a second delay element having in input coupled to an output of the first delay element;
• and
• a multiplexer, having a first input coupled to the output of the first delay element and a second input coupled to an output of the second delay element, and having an output coupled to the first input of the XOR circuit, the multiplexer for selecting the output of the first delay element or the second delay element based on a frequency of the first reference signal.