Power control circuit for a radio frequency transmitter

A transmitter for transmitting a transmit signal at a power level within a predetermined range of output power levels, the transmitter comprising:

• a signal generator for generating the transmit signal, at an intermediate frequency;
• a first variable gain stage, coupled to the signal generator, for controlling a power level of the transmit signal at the intermediate frequency responsive to a first gain control signal;
• a signal upconvertor, coupled to the first variable gain stage, for converting the frequency of the transmit signal from the intermediate frequency to a radio frequency;
• a second variable gain stage, coupled to the signal upconvertor, for controlling the power level of the transmit signal at the radio frequency responsive to a second gain control signal;
• and
• a gain controller, coupled to the first variable gain stage and the second variable gain stage, for providing the first gain control signal and the second gain control signal responsive to an output power level control signal, wherein the first gain control signal controls a gain of the first variable gain stage to vary the power level of the transmit signal at the intermediate frequency causing the output power level of the transmit signal to vary over a lower range of the predetermined range of output power levels, and wherein the second gain control signal controls a gain of the second variable gain stage to vary the power level of the transmit signal at the radio frequency causing the output power level of the transmit signal to vary over an upper range of the predetermined range of output power levels;
• wherein the gain controller further comprises:
• a crossover circuit for providing continuous output power level control of the transmit signal between the lower range and the upper range of the predetermined range of the output power levels by controlling the first gain control signal and the second gain control signal responsive to the output power level control signal and a crossover threshold signal,
• wherein the crossover circuit further comprises:
• a first clamp, coupled to receive the output power level control signal and the crossover threshold signal, for producing a first clamp output signal representative of the first gain control signal, wherein a level of the first clamp output signal is clamped to a level of the crossover threshold signal when a level of the output power control signal is greater than the level of the crossover threshold signal, and wherein the level of the first clamp output signal is equal to the level of the output power level control signal when the level of the output power control signal is less than the level of the crossover threshold signal;
• and
• a second clamp, coupled to receive the output power level control signal and the crossover threshold signal, for producing a second clamp output signal representative of the second gain control signal, wherein a level of the second clamp output signal is clamped to a level of the crossover threshold signal when a level of the output power control signal is less than the level of the crossover threshold signal, and wherein the level of the second clamp output signal is equal to the level of the output power level control signal when the level of the output power control signal is greater than the level of the crossover threshold signal,
• wherein the gain controller further comprises:
• a first linear transformer, coupled to receive the first clamp output signal from the first clamp, for converting the first clamp output signal to a first linear transformer output signal representative of the first gain control signal;
• and
• a second linear transformer, coupled to receive the second clamp output signal from the second clamp, for converting the second clamp output signal to a second linear transformer output signal representative of the second gain control signal, and
• wherein the gain controller further comprises:
• a first predistortion circuit, coupled to the first linear transformer, for predistorting the first gain control signal responsive to the first linear transformer output signal to compensate for nonlinearities in a first transfer function representative of gain as a function of the first gain control signal for the first variable gain stage;
• and
• a second predistortion circuit, coupled to the second linear transformer, for predistorting the second gain control signal responsive to the second linear transformer output signal to compensate for nonlinearities in a second transfer function representative of gain as a function of the second gain control signal for the second variable gain stage.

A transmitter for transmitting a transmit signal at a power level within a predetermined range of output power levels, the transmitter comprising:

• a signal generator for generating the transmit signal at an intermediate frequency, wherein the signal generator further comprises:
• a transmit intermediate frequency local oscillator for providing a transmit intermediate frequency local oscillator signal;
• and
• a modulator for modulating the transmit intermediate frequency local oscillator signal with an information signal to produce the transmit signal at the intermediate frequency;
• a first variable gain stage, coupled to the signal generator, for controlling a power level of the transmit signal at the intermediate frequency responsive to a first gain control signal;
• a signal upconvertor, coupled to the first variable gain stage, for converting the frequency of the transmit signal from the intermediate frequency to a radio frequency, wherein the signal upconvertor further comprises:
• a transmit radio frequency local oscillator for providing a transmit radio frequency local oscillator signal;
• a mixer for upconverting the transmit signal at the intermediate frequency to the transmit signal at the radio frequency responsive to the transmit radio frequency local oscillator signal;
• and
• a second variable gain stage, coupled to the signal upconvertor, for controlling the power level of the transmit signal at the radio frequency responsive to a second gain control signal;
• and
• a gain controller, coupled to the first variable gain stage and the second variable gain stage, for providing the first gain control signal and the second gain control signal responsive to an output power level control signal, wherein the first gain control signal controls a gain of the first variable gain stage to vary the power level of the transmit signal at the intermediate frequency causing the output power level of the transmit signal to vary over a lower range of the predetermined range of output power levels, and wherein the second gain control signal controls a gain of the second variable gain stage to vary the power level of the transmit signal at the radio frequency causing the output power level of the transmit signal to vary over an upper range of the predetermined range of output power levels,
• wherein the gain controller further comprises:
• a crossover circuit for providing continuous output power level control of the transmit signal between the lower range and the upper range of the predetermined range of the output power levels by controlling the first gain control signal and the second gain control signal responsive to the output power level control signal and a crossover threshold signal,
• wherein the crossover circuit further comprises:
• a first clamp, coupled to receive the output power level control signal and the crossover threshold signal, for producing a first clamp output signal representative of the first gain control signal, wherein a level of the first clamp output signal is clamped to a level of the crossover threshold signal when a level of the output power control signal is greater than the level of the crossover threshold signal, and wherein the level of the first clamp output signal is equal to the level of the output power level control signal when the level of the output power control signal is less than the level of the crossover threshold signal;
• and
• a second clamp, coupled to receive the output power level control signal and the crossover threshold signal, for producing a second clamp output signal representative of the second gain control signal, wherein a level of the second clamp output signal is clamped to a level of the crossover threshold signal when a level of the output power control signal is less than the level of the crossover threshold signal, and wherein the level of the second clamp output signal is equal to the level of the output power level control signal when the level of the output power control signal is greater than the level of the crossover threshold signal.

A code division multiple access (CDMA) radiotelephone comprising:

• a receiver for receiving a closed loop correction signal and for generating a received signal strength indication (RSSI) signal;
• and
• a transmitter for transmitting a transmit signal at a power level within a predetermined range of output power levels, the transmitter comprising:
• a radiotelephone controller for providing a first gain control signal and a second gain control signal responsive to the output power level control signal, wherein the output power level control signal is a sum of a channel gain adjust signal, the received signal strength indication signal and the closed loop correction signal;
• a signal generator for generating the transmit signal at an intermediate frequency;
• a first variable gain stage, coupled to the signal generator, for controlling a power level of the transmit signal at the intermediate frequency responsive to a first gain control signal;
• a signal upconvertor, coupled to the first variable gain stage, for converting the frequency of the transmit signal from the intermediate frequency to a radio frequency;
• a second variable gain stage, coupled to the signal upconvertor, for controlling the power level of the transmit signal at the radio frequency responsive to a second gain control signal;
• and
• a gain controller, coupled to the first variable gain stage and the second variable gain stage, for providing the first gain control signal and the second gain control signal responsive to an output power level control signal, wherein the first gain control signal controls a gain of the first variable gain stage to vary the power level of the transmit signal at the intermediate frequency causing the output power level of the transmit signal to vary over a lower range of the predetermined range of output power levels, and wherein the second gain control signal controls a gain of the second variable gain stage to vary the power level of the transmit signal at the radio frequency causing the output power level of the transmit signal to vary over an upper range of the predetermined range of output power levels,
• wherein the gain controller further comprises:
• a crossover circuit for providing continuous output power level control of the transmit signal between the lower range and the upper range of the predetermined range of the output power levels by controlling the first gain control signal and the second gain control signal responsive to the output power level control signal and a crossover threshold signal,
• wherein the crossover circuit further comprises:
• a first clamp, coupled to receive the output power level control signal and the crossover threshold signal, for producing a first clamp output signal representative of the first gain control signal, wherein a level of the first clamp output signal is clamped to a level of the crossover threshold signal when a level of the output power control signal is greater than the level of the crossover threshold signal, and wherein the level of the first clamp output signal is equal to the level of the output power level control signal when the level of the output power control signal is less than the level of the crossover threshold signal;
• and
• a second clamp, coupled to receive the output power level control signal and the crossover threshold signal, for producing a second clamp output signal representative of the second gain control signal, wherein a level of the second clamp output signal is clamped to a level of the crossover threshold signal when a level of the output power control signal is less than the level of the crossover threshold signal, and wherein the level of the second clamp output signal is equal to the level of the output power level control signal when the level of the output power control signal is greater than the level of the crossover threshold signal.

A method for controlling an output power level of a transmit signal within a predetermined range of output power levels, the method comprising the steps of:

• varying a power level of the transmit signal at an intermediate frequency to produce the output power level for the transmit signal within a lower range of the predetermined range of output power levels;
• varying a power level of the transmit signal at a radio frequency to produce the output power level for the transmit signal within an upper range of the predetermined range of output power levels;
• determining the output power level for the transmit signal;
• and
• comparing the output power level to an output power crossover threshold level;
• wherein the step of varying the power level of the transmit signal at an intermediate frequency is performed when the output power level is less than the output power crossover threshold level to produce the output power level for the transmit signal, and
• wherein the step of varying the power level of the transmit signal at a radio frequency is performed when the output power level is greater or equal to than the output power crossover threshold level to produce the output power level for the transmit signal.

A method for operating a code division multiple access (CDMA) radiotelephone comprising the steps of:

• receiving a closed loop correction signal;
• generating a received signal strength indication (RSSI) signal;
• generating an output power control signal responsive to the closed loop correction signal, the RSSI signal and a channel gain adjust signal;
• transmitting a transmit signal at an output power level within a predetermined range of output power levels responsive to the output power control signal, the step of transmitting further comprising the steps of:
• varying a power level of the transmit signal at an intermediate frequency to produce the output power level for the transmit signal within a lower range of the predetermined range of output power levels;
• varying a power level of the transmit signal at a radio frequency to produce the output power level for the transmit signal within an upper range of the predetermined range of output power levels;
• determining the output power level for the transmit signal;
• and
• comparing the output power level to an output power crossover threshold level;
• wherein the step of varying the power level of the transmit signal at an intermediate frequency is performed when the output power level is less than the output power crossover threshold level to produce the output power level for the transmit signal, and
• wherein the step of varying the power level of the transmit signal at a radio frequency is performed when the output power level is greater or equal to than the output power crossover threshold level to produce the output power level for the transmit signal.