PLL and phase detection circuit therefor

An integrated circuit including a frequency synthesizer for receiving a first signal at a first frequency and for generating a second signal at a second frequency, the frequency synthesizer comprising:

• a phase detection circuit for receiving a first input signal indicative of the first signal of the frequency synthesizer, and for receiving a second input signal indicative of the second signal of the frequency synthesizer, the phase detection circuit comprising:
• an exclusive gate having first and second gate inputs for receiving first and second gate input signals, and a gate output providing a gate output signal that is the exclusive combination of the first and second gate input signals, the first gate input signal being the first signal and the second gate input signal being the second signal;
• a first effective resistance coupled between a first voltage source and a common node;
• a second effective resistance coupled between a second voltage source and the common node, the second effective resistance receiving the gate output signal to control the effective resistance thereof, the first and second resistance cooperating to develop a signal at the common node;
• and
• a comparator having first and second comparator inputs and a comparator output, the first comparator input coupled to the common node, the second comparator input coupled to a threshold value, the comparator output providing a signal that takes on a first value when the average value of the signal developed at the common node is greater than the threshold value, and a second value when the average value of the signal developed at the common node is less than the threshold value, whereby the comparator output signal is indicative of whether the first and second input signals to the exclusive gate are in phase;
• an oscillator control circuit for receiving the comparator output, and for providing an oscillator control signal in response to the comparator output;
• and
• an oscillator for receiving the oscillator control signal and for producing the second signal, the oscillator capable of adjusting the phase of the second signal in response to the control signal.

An integrated circuit including a phase detection circuit, comprising:

• an exclusive OR gate having first and second gate inputs for receiving first and second gate input signals, and a gate output providing a gate output signal that is the exclusive OR combination of the first and second gate input signals;
• a first effective resistance coupled between a first voltage source and a common node;
• a second effective resistance coupled between a second voltage source and the common node, the second effective resistance including a transistor, the transistor having a first terminal coupled to the second voltage source, a second terminal coupled to the common node, and a control terminal coupled to the gate output signal to control the effective resistance of the second effective resistance in response to the gate output signal, the first effective resistance and second effective resistance cooperating to develop a signal at the common node;
• a comparator having a comparator input, a threshold input, and an output, the comparator input coupled to the common node and the threshold input coupled to a predetermined threshold value, the comparator output providing a signal that takes on a first value when the average value of the signal developed at the common node is greater than the predetermined threshold value, and a second value when the average value of the signal developed at the common node is less than the predetermined threshold value, whereby the comparator output signal is indicative of whether the first and second gate input signals to the exclusive OR gate are in phase.