Transmitter circuits
A polar loop transmitter includes separate phase and envelope paths providing a linearising scheme for an efficient non-linear power amplifier. Loop filters are included in each of the phase and envelope paths to enable the path characteristics to be matched to one another. A polar loop transmitter and other types of envelope elimination and restoration transmitters control the output envelope of the power amplifier by connecting the output of the envelope detector, or in an envelope feedback transmitter, the envelope error signal, to the bias control input of the power amplifier. The transmitter can further include compensation means for compensating for non-linearities in the envelope control means and a loss of feedback control detector to ensure that the feedback signal remains within acceptable limits.
1. A polar loop transmitter, comprising:
an envelope loop;
a phase loop; and
components disposed within each of the phase and envelope loops configured to match the transfer characteristics of the phase and envelope loops, wherein said matching components comprise a loop filter in each of the phase and envelope loops, the polar loop transmitter being operable over an operating frequency range, wherein each loop filter is configured so that the transfer characteristics of the phase and envelope loops are matched over the operating frequency range.
2. A polar loop transmitter according to claim 1 , including a power amplifier for providing an output signal, wherein the envelope loop includes an envelope control system for the output signal.
3. A polar loop transmitter according to claim 2 , wherein the envelope control system includes a power supply modulator arranged to modulate the voltage supply of the power amplifier.
4. A polar loop transmitter according to claim 2 , wherein the envelope loop includes an envelope detector.
5. A polar loop transmitter according to claim 4 , wherein the envelope detector is connected to a bias control input of the power amplifier, whereby to provide the envelope control system.
6. A polar loop transmitter according to claim 2 , further comprising compensation means disposed in the envelope loop for compensating for non-linearities in the envelope control system.
7. A polar loop transmitter according to claim 2 , comprising first and second envelope detectors for detecting input and output envelopes respectively and a system for providing a difference signal representative of the difference between the input and output envelopes.
8. A polar transmitter according to claim 7 , wherein said difference signal providing system comprises a comparator.
9. A polar loop transmitter according to claim 7 , further comprising a detector configured to detect loss of feedback control.
10. A polar loop transmitter according to claim 9 , wherein the detector is operative on the difference signal.
11. A polar loop transmitter comprising:
an envelope loop;
a phase loop; and
components disposed within each of the phase and envelope loops configured to match the transfer characteristics of the phase and envelope loops, wherein said matching components comprise a loop filter in each of the phase and envelope loops, wherein each loop filter is configured so that the phase and envelope loops are of the same type and have substantially the same bandwidth and loop damping.
12. A polar loop transmitter comprising:
a power amplifier for amplifying an input signal having input phase and envelope components to produce an output signal having output phase and envelope components;
an envelope loop including elements configured to produce an envelope difference signal representative of the difference between the input and output envelope components, said envelope loop having a loop transfer characteristic;
a phase loop including elements configured to produce a phase difference signal representative of the difference between the input and output phase components, said phase loop having a loop transfer characteristic; and
elements disposed within each of the phase and envelope loops configured to match the transfer characteristics of the phase and envelope loops.
13. A portable communications device including a polar loop transmitter composing:
a power amplifier for amplifying an input signal having input phase and envelope components to produce an output signal having output phase and envelope components;
an envelope loop including elements configured to produce an envelope difference signal representative of the difference between the input and output envelope components, said envelope loop having a loop transfer characteristic;
a phase loop including elements configured to produce a phase difference signal representative of the difference between the input and output phase components, said phase loop having a loop transfer characteristic; and
elements disposed within each of the phase and envelope loops configured to match the transfer characteristics of the phase and envelope loops.
14. An envelope feedback transmitter including a power amplifier providing an output signal;
a controller for controlling the envelope of the output signal; and
a compensator for compensating for non-linear characteristics of the envelope controller wherein the power amplifier has a bias control input the feedback transmitter further comprising a difference signal generator means for providing a difference signal representative of the difference between input and output envelope components, wherein the difference signal is connected to the bias control input of the power amplifier to provide the envelope control means, wherein the difference signal generator comprises a comparator arranged to receive signals from first and second envelope detectors for detecting the input and output envelope components respectively, wherein the compensator is disposed between the output of the amplifier and the input to the comparator, and wherein the compensator comprises first and second compensation elements, the first compensation element being disposed between the first envelope detector and a first input to the comparator and the second compensation element being disposed between the second envelope detector and a second input to the comparator.
15. An envelope feedback transmitter according to claim 14 , wherein the first and second compensation elements have a large signal transfer function which approximates to the inverse of the large signal transfer function of the envelope control means.
16. An envelope feedback transmitter including a power amplifier providing an output signal,
a controller for controlling the envelope of the output signal; and
a compensator for compensating for non-linear characteristics of the envelope controller, wherein the power amplifier has a bias control input, the feedback transmitter further comprising a difference signal generator means for providing a difference signal representative of the difference between input and output envelope components, wherein the difference signal is connected to the bias control input of the power amplifier to provide the envelope control means, wherein the difference signal generator comprises a comparator arranged to receive signals from first and second envelope detectors for detecting the input and output envelope components respectively, wherein the compensator is disposed between the output of the comparator and the envelope controller, and wherein the compensation element has a linear transfer function with variable gain and a non-linear gain control.
17. An envelope feedback transmitter according to claim 16 , wherein the non-linear gain control is connected to either one of the first and second envelope detectors.