A unique method and apparatus modifies the load impedance at the output of a power amplifier by varying a voltage variable capacitor (VVC) (310) to maximize the efficiency of the power amplifier (304) A comparator (509) generates amplifier control signal (211) based upon a detected power output signal (216) and a reference signal In addition to providing power control, the control signal is also coupled to a VVC circuit (506) to control the output impedance of the power amplifier In an alternate embodiment, a separate VVC control signal (527) based upon a comparison of the power control signal and the battery voltage is coupled to a VVC In another alternate embodiment, a second VVC can be coupled in parallel to the first VVC The second VVC is preferably controlled by a signal (805) based upon the current in the power amplifier Finally, an alternate embodiment incorporates a VVC circuit (506) at the input of the power amplifier to compensate for variations in input impedance to improve other power amplifier parameters such as IM, gain, output power and noise level

Method and apparatus for amplifying a signal

The present invention, generally speaking, incorporates the power amplifier as a fundamental constituent of a modulator, using polar modulation techniques. Thus, it is possible to achieve the combination of precision signal generation (including envelope variations) along with high energy efficiency in combinations not possible heretofore. In accordance with one embodiment of the invention, a modulated radio (passband) signal generator produces high quality signals of general type, which specifically includes signals with varying envelopes. Signals are generated with high energy efficiency in the conversion of applied DC power to output RF signal power. The result is longer battery life for products such as mobile phone handsets. Dramatically improved efficiency also allows for a dramatic reduction (10 to 1 or greater) in the size of any required heatsink for the radio transmitter, which significantly lowers both cost and size. Furthermore, continuous operation of these radio transmitters is made possible with small temperature rises using small heatsinks, or even without any heatsink components. This provides for high operating reliability, as well as for greater throughput due to the longer operating time allowed. Another aspect of the invention allows the generation of high quality signals with wide bandwidth, without the need for continuous feedback during operation. This further reduces costs by greatly simplifying the design, manufacturing, and complexity of the transmitter circuitry.

High-efficiency power modulators

Improved temperature compensated, automatic output control (AOC) circuitry for RF signal power amplifiers is described that maintains the output power within one-half dB of a selected one of eight power levels varying from nine milliwatts to five watts, a dynamic range of twenty-eight dB. The amplification of the RF signal amplifier is proportional to a drive current signal provided by a current amplifier. A half-wave rectifier is coupled to the output of final amplifiers for generating an output power signal that has a magnitude proportional to the output power. The half-wave rectifier is temperature compensated for and biased by a diode coupled to the rectifier by one resistor and coupled to supply voltage by another resistor. The output power voltage is further coupled to an amplifier having an amplification factor selected by level control signals. The amplified output power signal is coupled to a comparator which varies the drive current provided by the current amplifier in response to the voltage difference between the amplified output power signal and a reference voltage.

Temperature compensated automatic output control circuitry for RF signal power amplifiers with wide dynamic range

A power amplifier controller for detecting saturation of the power amplifier (203) and correcting the automatic output control voltage (231) to avoid any further saturation. The controller detects the power of the RF output signal (211), generates a signal (229) correlated to the detected power, compares changes in that signal (229) to changes in the voltage of the AOC signal (231) in a comparator (217). The comparator (217) generates a signal (233) correlated to saturation of the power amplifier (203) for a DSP (223). The DSP checks the status of this signal (233). Upon detecting saturation, an algorithm contained within the DSP methodically reduces the voltage of the AOC signal (231) until there is a change in the power of the RF output signal (211).

Power amplifier saturation detection and correction method and apparatus

The present invention, generally speaking, provides for high-efficiency power control of a high-efficiency (e.g., hard-limiting or switch-mode) power amplifier. In one embodiment, the invention exploits the recognition that, for a constant-resistance circuit, power is equal to the square of the voltage across the circuit divided by the resistance of the circuit. In the case of certain switch mode amplifiers, such as Class E and Class F amplifiers, as well as saturated linear amplifiers, the amplifier may reasonably be regarded as having a constant resistance with varying power supply. In an exemplary embodiment, the supply voltage is controlled using a combination of two stages, a switch-mode converter stage that accomplishes gross power level control and a subsequent linear regulator stage that accomplishes more precise power envelope control, e.g., burst control. Control circuitry for the amplifier is simplified by combining control signals for power amplifier ramp-up transition, power level during a TDMA burst, and ramp-down transition, into a single control signal, and by eliminating feedback control (which also eliminates errors in the feedback control of output power due to the use of detecting diodes). Output noise from the variable output switch-mode voltage converter stage is filtered using the linear regulator stage that accomplishes burst control, further increasing circuit efficiency. Energy efficiency during ramp-up to the desired output power, during the burst at all output power levels, and during ramp-down from the transmitted power, is maximized. Reasonable expected efficiencies for the switch-mode converter stage and the linear regulator stage are 90% and 80%, respectively. A high-efficiency switch-mode amplifier may have an efficiency on the order of 80%, enabling an overall efficiency of greater than 50% to be achieved, comparing very favorably with current efficiencies of about 10%.

High-efficiency amplifier output level and burst control

A multistage radio frequency (RF) signal power amplifier is described that utilizes microstrip transmission line techniques for realizing essentially all of the matching circuitry for each stage of amplification. The power amplifier includes a variable gain predriver, a driver amplifier and a pair of paralleled final amplifiers, all of which are intercoupled by microstrip coupling circuitry. A power detector senses the magnitude of the final amplifier output and provides a forward power signal having a magnitude proportional thereto. A power output regulator is responsive to the forward power signal for providing a drive signal for varying the gain of the predriver amplifier to maintain the magnitude of the final amplifier output at a preset magnitude. The RF signal power amplifier further includes spurious signal suppression circuitry coupled to the output of the driver amplifier and final amplifiers for suppressing spurious signals generated by regenerative modes of oscillation occurring therein. The spurious signal suppression circuitry includes a resistor coupled to a microstrip transmission line having a length such that the line is a relatively low impedance at the spurious signal frequencies and a high impedance at the RF signal frequency. Thus, the spurious signals are attenuated by the resistor, while the RF signal is essentially unaffected. The RF signal power amplifier embodying the present invention may be advantageously utilized in a radio communication system for amplifying signals to be transmitted by a base station radio.

Thomas W. Hull

Papers

Radio frequency signal power amplifier