High frequency power amplification electric part and wireless communication system
View Patent ↗The present invention provides a high frequency amplifier suitable for use in a wireless communication system which performs detection of an output level necessary for feedback control by a current detection system, wherein control sensitivity in an area low in transmit request level is lowered so that an output level can be controlled over the whole control range with satisfactory accuracy. There is provided a high frequency power amplification electric part constituting a wireless communication system, which performs detection of an output level necessary for feedback control of output power by a current detection system, compares the output level detected signal and an output level designation signal and generates a bias voltage for a high frequency power amplifier according to the difference therebetween to thereby control gain, wherein an nth root converter or a logarithm converter is provided between a current detector and a current-voltage converter.
1. A power amplifier circuit for use in a wireless communication system, the power amplifier circuit comprising:
a power amplifier coupled to receive an input signal and amplifying the input signal to provide an output signal;
a first converter coupled to receive the output signal of the power amplifier and providing a first signal which follows a power of the output signal;
a non-linear converter coupled to receive the first signal and providing a second signal;
a second converter coupled to receive the second signal and providing a voltage based on the second signal;
an error amplifier coupled to both the voltage and an output level designation signal and providing a third signal corresponding to a difference therebetween; and
a bias circuit coupled to receive the third signal and providing to the power amplifier a bias in accordance with the third signal,
wherein the non-linear converter is an nth root converter converting the first signal into the second signal obtained by extracting the nth (where n is a positive integer) root of the first signal.
2. A power amplifier circuit according to claim 1 ,
wherein the nth root converter is a square root converter.
3. A power amplifier circuit according to claim 2 ,
wherein the square root converter is a circuit including field effect transistors and which receives the first signal and a reference current as input signals and outputs a current obtained by extracting the square root of the product of both the first signal and the reference current.
4. A power amplifier circuit for use in a wireless communication system, the power amplifier circuit comprising:
a power amplifier coupled to receive an input signal and amplifying the input signal to provide an output signal;
a first converter coupled to receive the output signal of the power amplifier and providing a first signal which follows a power of the output signal;
a non-linear converter coupled to receive the first signal and providing a second signal;
a second converter coupled to receive the second signal and providing a voltage based on the second signal;
an error amplifier coupled to both the voltage and an output level designation signal and providing a third signal corresponding to a difference therebetween; and
a bias circuit coupled to receive the third signal and providing to the power amplifier a bias in accordance with the third signal,
wherein the non-linear converter is a logarithm converter converting the first signal into the second signal obtained by log-transforming the first signal and outputs it therefrom,
wherein the logarithm converter includes:
a pair of diodes which receive the first signal and a reference current as input signals and cause the first signal and the reference current to flow therethrough respectively,
differential amplifiers which receive voltages converted by the diodes as inputs and output voltages each corresponding to the difference between the voltages, and
a temperature compensating device which compensates for temperature characteristics of the diodes, and outputs a temperature dependence-free voltage.
5. A power amplifier circuit according to claim 4 ,
wherein the logarithm converter includes a first-stage circuit having bipolar transistors.
6. A power amplifier circuit for use in a wireless communication system, the power amplifier circuit comprising:
a power amplifier coupled to receive an input signal and amplifying the input signal to provide an output signal;
a first converter coupled to receive the output signal of the power amplifier and providing a first signal which follows a power of the output signal;
a non-linear converter coupled to receive the first signal and providing a second signal;
a second converter coupled to receive the second signal and providing a voltage based on the second signal;
an error amplifier coupled to both the voltage and an output level designation signal and providing a third signal corresponding to a difference therebetween; and
a bias circuit coupled to receive the third signal and providing to the power amplifier a bias in accordance with the third signal,
wherein the first converter comprises: an output detecting transistor, and a current mirror circuit which includes a first transistor coupled in series with the output detecting transistor and a second transistor whose control terminal is mutually coupled in common to a control terminal of the first transistor, and
wherein the non-linear converter receives an output of the current mirror circuit as said first signal and outputs the second signal.