Noise immunity circuitry for phase locked loops and delay locked loops

1. A clock circuit comprising:

a phase detector coupled to receive a reference clock signal and an output clock signal and configured to provide a phase signal indicative of a phase difference between the reference clock signal and the output clock signal; and

an output unit configured to provide the output clock signal, wherein the output unit is coupled to a first supply voltage node and a second supply voltage node, and wherein the output unit includes:

a biasing circuit coupled to receive a control voltage based on the phase signal and configured to generate, based on the control voltage, a bias voltage on a bias voltage node, wherein the bias voltage is decoupled from the second supply voltage node, wherein the biasing circuit includes an amplifier having an inverting input, a non-inverting input, and an output, wherein the inverting input is coupled to receive the control voltage; and

a voltage-controlled element coupled to the first supply voltage node and the bias voltage node, and wherein the voltage-controlled element is configured to adjust a parameter of the output clock signal based on the bias voltage.

2. The clock circuit as recited in claim 1 , wherein the reference clock signal, the output clock signal, the phase signal, the control voltage, and the bias voltage are each single-ended signals.

3. The clock circuit as recited in claim 1 further comprising a charge pump, wherein the charge pump is coupled to receive the phase signal and is configured to generate the control voltage based on the phase signal.

4. The clock circuit as recited in claim 3 , wherein the control voltage is provided on a control voltage node, and wherein the clock circuit further includes a low-pass filter coupled between the first supply voltage node and the control voltage node.

5. The clock circuit as recited in claim 1 , wherein the biasing circuit further includes a transistor, wherein a gate terminal of the transistor is coupled to the output of the amplifier, and wherein a channel of the transistor is coupled between the bias voltage node and the second supply voltage node.

6. The clock circuit as recited in claim 1 , wherein the non-inverting input of the amplifier is coupled to the bias voltage node.

7. The clock circuit as recited in claim 1 , further comprising a coupling capacitance coupled between the first supply voltage node and the bias voltage node.

8. The clock circuit as recited in claim 1 , wherein the clock circuit is a delay locked loop, and wherein the voltage-controlled element is a voltage controlled delay line, wherein the voltage controlled delay line is coupled to receive the reference clock signal and provide the output clock signal as a delayed version of the reference clock signal, wherein an amount of delay provided is based on the bias voltage.

9. The clock circuit as recited in claim 1 , wherein the clock circuit is a phase locked loop, and wherein the voltage-controlled element is a voltage-controlled oscillator, and wherein a frequency of the output clock signal is based on the bias voltage.

10. The clock circuit as recited in claim 1 , wherein the clock circuit further includes a level shifting circuit coupled to receive the output clock signal from the voltage-controlled element, wherein the level shifting circuit is configured to provide the output clock signal at a shifted voltage level.

11. A delay locked loop comprising:

a phase detector coupled to receive a reference clock signal and an output clock signal and configured to provide a phase signal indicative of a phase difference between the reference clock signal and the output clock signal;

a voltage-controlled delay line coupled to a first supply voltage node and a bias voltage node, wherein the voltage-controlled delay line is coupled to receive the reference clock signal; and

a biasing circuit coupled to the first supply voltage node and a second supply voltage node, wherein the biasing circuit is further coupled to receive a control voltage based on the phase signal and configured to generate a bias voltage based on the control voltage, wherein the bias voltage is decoupled from the second supply voltage node, wherein the biasing circuit includes an amplifier having an inverting input, a non-inverting input, and an output, wherein the inverting input is coupled to receive the control voltage;

wherein the voltage-controlled delay line is configured to adjust an amount of delay of the output clock signal with respect to the reference clock signal based on the bias voltage.

12. The delay locked loop as recited in claim 11 , wherein the reference clock signal, the output clock signal, the phase signal, the control voltage, and the bias voltage are each single-ended signals.

13. The delay locked loop as recited in claim 11 , wherein the biasing circuit further includes a transistor, wherein a gate terminal of the transistor is coupled to the output of the amplifier, and wherein a channel of the transistor is coupled between the bias voltage node and the second supply voltage node, and wherein the non-inverting input of the amplifier is coupled to the bias voltage node.

14. The delay locked loop as recited in claim 11 further comprising a charge pump, wherein the charge pump is coupled to receive the phase signal and is configured to generate the control voltage based on the phase signal, wherein the control voltage is provided on a control voltage node, and wherein the clock circuit further includes a filter capacitance coupled between the first supply voltage node and the control voltage node.

15. A phase locked loop comprising:

a phase detector coupled to receive a reference clock signal and an output clock signal and configured to provide a phase signal indicative of a phase difference between the reference clock signal and the output clock signal;

a voltage controlled oscillator coupled to a first supply voltage node and a bias voltage node; and

a biasing circuit coupled to the first supply voltage node and a second supply voltage node, wherein the biasing circuit is further coupled to receive a control voltage based on the phase signal and configured to generate a bias voltage based on the control voltage, wherein the bias voltage is decoupled from the second supply voltage node, wherein the biasing circuit includes an amplifier having an inverting input, a non-inverting input, and an output, wherein the inverting input is coupled to receive the control voltage, wherein the biasing circuit further includes a transistor, wherein a gate terminal of the transistor is coupled to the output of the amplifier, and wherein a channel of the transistor is coupled between the bias voltage node and the second supply voltage node, and wherein the non-inverting input of the amplifier is coupled to the bias voltage node;

wherein the voltage controlled oscillator is configured to generate the output clock signal based on the bias voltage.

16. The phase locked loop as recited in claim 15 , wherein the reference clock signal, the output clock signal, the phase signal, the control voltage, and the bias voltage are each single-ended signals.

17. The phase locked loop as recited in claim 15 , further comprising a charge pump, wherein the charge pump is coupled to receive the phase signal and is configured to generate the control voltage based on the phase signal, wherein the control voltage is provided on a control voltage node, and wherein the clock circuit further includes a filter capacitance coupled between the first supply voltage node and the control voltage node.

18. A clock circuit comprising:

a phase detector coupled to receive a reference clock signal and an output clock signal and configured to provide a phase signal indicative of a phase difference between the reference clock signal and the output clock signal; and

an output unit configured to provide the output clock signal, wherein the output unit is coupled to a first supply voltage node and a second supply voltage node, and wherein the output unit includes:

a biasing circuit coupled to receive a control voltage based on the phase signal and configured to generate, based on the control voltage, a bias voltage on a bias voltage node, wherein the bias voltage is decoupled from the second supply voltage node;

a voltage-controlled element coupled to the first supply voltage node and the bias voltage node, and wherein the voltage-controlled element is configured to adjust a parameter of the output clock signal based on the bias voltage; and

a level shifting circuit coupled to receive the output clock signal from the voltage-controlled element, wherein the level shifting circuit is configured to provide the output clock signal at a shifted voltage level.