Charge pump circuit for a phase locked loop

A circuit, comprising:

• a first current source coupled between a power supply node and a first node;
• a first switch coupled between the first node and a second node and controlled by a first control signal;
• a second switch coupled between the second node and a third node and controlled by a second control signal;
• a second current source coupled between the third node and a ground node;
• a third switch coupled between the first node and an output node and controlled by a complement of the first control signal;
• a fourth switch coupled between the second node and the output node and controlled by a third control signal;
• a fifth switch coupled between the second node and a fourth node and controlled by the third control signal;
• a first capacitor coupled between the second node and the fourth node;
• a second capacitor coupled between the second node and ground;
• a sixth switch coupled between the fourth node and a fifth node and controlled by an inverse of the third control signal;
• a loop filter coupled between the fifth node and ground;
• an amplifier having a non-inverting terminal coupled to the fifth node, an inverting terminal coupled to the output node, and an output terminal coupled to the output node;
• and
• a seventh switch coupled between the output node and the third node and controlled by an inverse of the second control signal.

A circuit, comprising:

• a first current source coupled between a power supply node and a first node;
• a first switch coupled between the first node and a second node and controlled by a first control signal;
• a second switch coupled between the second node and a third node and controlled by a second control signal;
• a second current source coupled between the third node and a ground node;
• a first resistor coupled between the second node and a fifth node;
• a second resistor coupled between the second node and a fourth node;
• a third switch coupled between the fourth node and a sixth node and controlled by a third control signal;
• a loop filter coupled between the fifth node and ground;
• and
• an amplifier having a non-inverting terminal coupled to the fifth node, an inverting terminal coupled to the sixth node, and an output terminal coupled to the sixth node.

A phase locked loop, comprising:

• a phase frequency detector (PFD) configured to compare phases of an input signal and a feedback signal, and to generate therefrom control signals;
• a logic circuit configured to compare phases of the input signal and the feedback signal, and to generate therefrom a selection signal indicating locking of the phased locked loop;
• a charge pump circuit to be selectively coupled in series with the PFD based upon the selection signal indicating that the phase locked loop has not locked and comprising:
• first and second current sources;
• a loop filter coupled between a voltage controlled oscillator (VCO) control node and a ground node;
• a buffer having an input coupled to the VCO control node;
• a first switch configured to couple the first current source to the VCO control node such that the voltage at the VCO control node increases, based upon the control signals indicating that the phase of the input signal leads the phase of the feedback signal,
• a second switch configured to couple the second current source to the VCO control node such that the voltage at the VCO control node decreases, based upon the control signals indicating that the phase of the feedback signal leads the phase of the input signal;
• an attenuation circuit to be selectively coupled in series with the PFD based upon the selection signal indicating that the phase locked loop has locked and comprising:
• first and second current sources;
• a loop filter coupled between a voltage controlled oscillator (VCO) control node and a ground node;
• a buffer having an input coupled to the VCO control node;
• an impedance network coupled to the VCO control node and comprising at least one impedance element configured to be:
• coupled to the first current source such that voltage at the VCO control node increases, based upon the control signals indicating that the phase of the input signal leads the phase of the feedback signal, and
• coupled to the second current source such that the voltage at the VCO control node decreases, based upon the control signals indicating that the phase of the feedback signal leads the phase of the input signal;
• a VCO coupled to the VCO control node and to generate an output signal based upon a signal at the VCO control node, the phase of the output signal matching the phase of the input signal;
• wherein the feedback signal is based upon the output signal.