Transmitter PLL with bandwidth on demand

1. A system, comprising a transmitter, wherein the transmitter comprises:

a phase locked loop (PLL) having a dynamically controllable loop bandwidth, the PLL comprising an oscillator;

a transmit modulator coupled to the PLL for performing vector modulation in response to transmission symbols, wherein each transmission symbol comprises an amplitude signal and a phase signal; and

a controller coupled to the PLL and to the transmit modulator operable to detect when a criteria of the transmission symbols crosses a threshold and to adjust loop bandwidth in response to the criteria crossing the threshold.

2. The system of claim 1 , wherein the criteria of the transmission symbols comprises a function of the amplitude signal or a function of the phase signal.

3. The system of claim 2 , wherein the function of amplitude signal is selected from a group consisting of the amplitude signal, a first derivative of the amplitude signal, a second derivative of the amplitude signal, a square of the amplitude signal, and a derivative of the amplitude signal squared.

4. The system of claim 2 , wherein the function of the phase signal is selected from the phase signal, and a derivative of the phase signal.

5. The system of claim 1 , wherein the controller is operable to make a first adjustment to the loop bandwidth when the criteria of the transmission symbols crosses a first threshold and to make a second adjustment to the loop bandwidth when the criteria crosses a second threshold.

6. The system of claim 5 , wherein the controller is operable to delay making the first adjustment by a programmable time delay.

7. The system of claim 1 , wherein the controller is operable to make a first adjustment to the loop bandwidth when the criteria of the transmission symbols crosses a first threshold and to make a second adjustment to the loop bandwidth after a time delay interval.

8. The system of claim 7 , wherein the controller is operable to delay making the first adjustment by a programmable time delay.

9. The system of claim 1 , wherein the controller is operable to increase the loop bandwidth in response to detecting criteria of the transmission symbols being above the threshold.

10. The system of claim 1 , wherein the controller is operable to decrease the loop bandwidth in response to detecting criteria of the transmission symbols being below the threshold.

11. The system of claim 1 , wherein the PLL comprises:

a frequency reference input for receiving a reference clock;

a controllable oscillator for generating a radio frequency (RF) clock;

a phase detection circuit operational to provide phase error samples indicative of phase difference between the RF clock and the reference clock for controlling the controllable oscillator; and

a programmable filter connected to receive the phase error samples and connected to provide a filtered output to the controllable oscillator, the programmable filter comprising a proportional loop gain control having a programmable loop coefficient (alpha), wherein the loop bandwidth is adjustable in response to alpha.

12. The system of claim 11 wherein the programmable filter further comprises an integral loop gain control having a programmable loop coefficient (rho), wherein the loop bandwidth is adjustable in response to rho.

13. The system of claim 11 , wherein the programmable filter further comprises one or more linear filters each having a programmable linear filter coefficient, coupled to first receive the phase error samples, wherein the loop bandwidth is adjustable in response to the linear filter coefficients.

14. The system of claim 13 , wherein the programmable filter coefficients are configured such that at least one linear filter coefficient is changed before or after changing alpha.

15. The system of claim 11 wherein the programmable filter further comprises:

an integral loop gain control having a programmable loop coefficient (rho), wherein the loop bandwidth is adjustable in response to rho;

one or more linear filters each having a programmable linear filter coefficient, coupled to first receive the phase error samples, wherein the loop bandwidth is adjustable in response to the linear filter coefficients; and

wherein the loop bandwidth is adjusted by changing one or more of a group consisting of the one or more programmable filter coefficients, alpha and rho.

16. The system of claim 15 , wherein two or more of the group are changed simultaneously.

17. The system of claim 15 , wherein one or more of the group are changed in multiple steps.

18. The system of claim 1 being a cellular telephone, wherein the PLL forms a local oscillator.

19. A method for operating digital system comprising a transmitter having a phase locked loop with a dynamically controllable bandwidth, comprising:

performing vector modulation in response to transmission symbols, wherein each transmission symbol comprises an amplitude signal and a phase signal;

detecting when a criteria of the transmission symbols crosses a threshold; and

adjusting loop bandwidth in response to the criteria crossing the threshold.

20. The method of claim 19 , wherein adjusting loop bandwidth comprises:

making a first adjustment to the loop bandwidth when the criteria of the transmission symbols crosses a first threshold; and

making a second adjustment to the loop bandwidth after a time delay interval.

21. The method of claim 19 , wherein adjusting loop bandwidth comprises:

making a first adjustment to the loop bandwidth when the criteria of the transmission symbols crosses a first threshold; and

making a second adjustment to the loop bandwidth when the criteria crosses a second threshold.

22. The method of claim 19 , wherein adjusting loop bandwidth comprises delaying making each adjustment by a programmable time delay.