Phase locked loop including an integrator-free loop filter
View Patent ↗A phase locked loop PLL having a forward path and a feedback path is disclosed. A phase detector drives an oscillator in the forward path of the phase locked loop. The feedback path includes a frequency divider that connects the oscillator output to the phase detector. The phase locked loop further includes an integrator-free loop filter configured to control the oscillator. The integrator-free loop filter enables a reduction in the required PLL bandwidth without reducing the signal quality when the PLL is used as a modulator.
1. A phase locked loop, comprising:
a phase detector comprising a first input configured to receive a reference signal, and a second input;
a controlled oscillator comprising a control input, and an output forming an output of the phase locked loop;
a frequency divider in a feedback path of the phase locked loop, the frequency divider comprising an input connected to the output of the controlled oscillator, and comprising an output connected to the second input of the phase detector; and
an integrator-free loop filter coupled between the output of the phase detector and the control input of the controlled oscillator, wherein the loop filter comprises a transfer function having at least one passive pole point in the Laplace plane.
2. The phase locked loop of claim 1 , wherein the loop filter comprises exclusively passive components.
3. The phase locked loop of claim 1 , wherein the at least one passive pole point is implemented by at least one associated RC element in the loop filter.
4. The phase locked loop of claim 1 , wherein the loop filter transfer function further comprises at least one complex-conjugate pole point pair in the Laplace plane.
5. The phase locked loop of claim 4 , wherein the loop filter comprises an operational amplifier.
6. The phase locked loop of claim 1 , further comprising a controlled current source having a control input connected to the output of the phase detector, and comprising a controlled path connected between a supply potential terminal and an input of the loop filter.
7. The phase locked loop of claim 6 , further comprising a resistor connected between the controlled current source and a reference potential.
8. A phase locked loop, comprising:
a phase detector configured to compare a reference signal to a divided feedback signal, and generate a control signal in response thereto;
a loop filter configured to receive the control signal and generate a tuning signal in response thereto, wherein the loop filter does not contain an integrating component, wherein the loop filter comprises:
an operational amplifier having a first input coupled to a reference potential, a second input, and an output forming an output of the loop filter;
a first capacitor coupled between the second input and the output of the operational amplifier;
a first resistor coupled between an intermediate node and the second input of the operational amplifier;
a second resistor coupled between the intermediate node and the output of the operational amplifier;
a second capacitor coupled between the intermediate node and the reference potential; and
a third resistor coupled between an input of the loop filter and the intermediate node, wherein the second capacitor and the third resistor form an RC element, or
wherein the loop filter comprises:
three series-connected RC elements extending between an input and an output of the loop filter, wherein each RC element comprises a resistor coupled between a respective input and a respective output, and a capacitor coupled between the respective output and a reference potential, or
wherein the loop filter comprises:
a transfer function having a complex-conjugate pole point pair in the Laplace plane without zero points;
a controlled oscillator configured to generate a phase locked loop output signal having a frequency that is a function of the tuning signal; and
a divider circuit in a feedback path configured to receive and divide down the phase locked loop output signal to form the divided feedback signal.
9. The phase locked loop of claim 8 , wherein the loop filter comprises a transfer function having at least one passive pole in the Laplace plane.
10. The phase locked loop of claim 8 , wherein the loop filter does not contain a pole at a zero location in the complex transfer function associated therewith.
11. A phase locked loop, comprising:
a phase detector configured to compare a reference signal to a divided feedback signal, and generate a control signal in response thereto;
a loop filter configured to receive the control signal and generate a tuning signal in response thereto, wherein the loop filter does not contain an integrating component;
a controlled oscillator configured to generate a phase locked loop output signal having a frequency that is a function of the tuning signal;
a divider circuit in a feedback path configured to receive and divide down the phase locked loop output signal to form the divided feedback signal; and
a controlled current source having a control input coupled to the output of the phase detector, and having a controlled current path coupled between a supply potential and an input of the loop filter, wherein a current in the controlled current path is a function of the control signal of the phase detector at the control input.
12. The phase locked loop of claim 11 , further comprising a load resistor coupled between the input of the loop filter and a reference potential, and configured to convert the current in the controlled current path to a voltage.