KR19990055425A - Structure of Power Amplifier with Phase Shifter Using Vector Modulator - Google Patents

Abstract

The present invention relates to a structure of a power amplifier having a phase shifting device using a vector modulator.

The linear modulation method is characterized in that both amplitude and phase of the modulated signal are changed. Therefore, a power amplifier having high linearity is required for the transmission of the linearly modulated signal. However, when the linear amplifier is used, the power efficiency is low, so the power efficiency is a big problem in applications where power efficiency is important, such as portable terminals. A method for solving such a decrease in power efficiency is a method using a Cartesian feedback loop. This method has high linearity and power efficiency by linearizing an amplifier with good power efficiency but nonlinear characteristics using a feedback loop. When using a Cartesian feedback loop, an apparatus is needed to compensate for the phase delay occurring in the loop.

According to the present invention, a phase shifting device for compensating for phase delay occurring in a loop is implemented by using a vector modulator. The structure of the power amplifier having a phase shifting device using a vector modulator capable of improving the accuracy of phase adjustment and a range of phase variation can be achieved. Is presented.

Description

Structure of Power Amplifier with Phase Shifter Using Vector Modulator

The present invention relates to a structure of a power amplifier having a phase shifting device using a vector modulator. In particular, a phase shifting device of a power amplifier using a Cartesian feedback loop is implemented by using a vector modulator. A power amplifier having a phase shifting device using a vector modulator that can be improved.

In linear modulation schemes such as quadrature amplitude modulation (QAM) and single side band (SSB) modulation, the waveform of a transmitted signal has a characteristic that both amplitude and phase change. Therefore, high linearity is required in the amplification stage of the linearly modulated signal. For this purpose, when the class A linear amplifier is used, power efficiency is reduced, so battery life time is a problem in the application of the portable terminal. On the other hand, there is a problem in that the linearity is not good when using a power-efficient class C amplifier.

A Cartesian feedback loop has been proposed to solve this problem of power efficiency degradation. This is achieved by linearizing a power amplifier with good power efficiency but nonlinear characteristics by using a feedback loop. It is a technology to design a power amplifier stage.

However, when using a Cartesian feedback loop to improve power efficiency, the phase delay occurring in the loop must be well compensated.

Accordingly, the present invention implements a phase shifting device for compensating for phase delay occurring in a loop by using a vector modulator to improve the accuracy of phase adjustment and a range of phase variation. The purpose is to provide a structure.

The structure of the power amplifier having a phase shifting device using a vector modulator according to the present invention for achieving the above object is a loop filter for maintaining the stability of the in-phase signal and the quadrature component signal input, and modulating the input signal A local oscillator for generating a carrier signal, a vector modulator for modulating the input signal stabilized through the loop filter at high frequency using a carrier signal input from the local oscillator, and the high frequency modulated signal through the vector modulator A high frequency power amplifier for amplifying an input signal to produce an appropriate transmit power, a directional coupler for sampling the input signal amplified through the high frequency power amplifier, and for delaying the phase of a carrier signal input through the local oscillator; Phase shifting device and the directional grain And a vector demodulator for demodulating the input signal sampled by the device using a carrier signal delayed by the phase shifting device, and a differential operator for matching and combining the phase of the input signal and the demodulated signal output from the vector demodulator. It features.

1 is a structural diagram of a power amplifier using a Cartesian feedback loop according to the present invention;

2 is a structural diagram of a phase shifting device using a vector modulator according to the present invention;

<Description of the symbols for the main parts of the drawings>

11: loop filter 12: modulator

13: high frequency amplifier 14: directional coupler

15 demodulator 16: local oscillator

17: phase shift device 18, 19: difference operator

21, 22: variable resistor 23, 24: multiplier

25: combiner

Hereinafter, with reference to the accompanying drawings will be described in detail the present invention.

1 is a structural diagram of a power amplifier using a Cartesian feedback loop.

The input signals Inphase (I) and Quadrature (Q) are baseband signals and the loop filter 11 is a lowpass filter for maintaining the stability of the loop. The input signals I and Q are modulated into a high frequency signal in the vector modulator 12 and passed through a high frequency power amplifier 13 to produce an appropriate transmit power. Since the high frequency power amplifier 13 used here has a nonlinear characteristic, the distortion component is added to the signal. Some of the modulated transmit power is sampled in the directional coupler 14 and then in the vector demodulator 15 And Is demodulated to a baseband signal of. The demodulated signal thus contains a distortion component generated by the nonlinear characteristic of the power amplifier. In the first-order operator 18 of the loop, I signal and Are subtracted from each other, and in the second order operator 19, The signals are subtracted from each other and this difference signal drives the loop. The loop can reduce the distortion caused by the nonlinearity of the power amplifier by the principle of the negative feedback system.

At this time, in the difference operators 18 and 19, , The phase of the signal must be subtracted, and if the phase difference is out of range, it affects the stability of the loop. This phase difference is due to the propagation delay experienced by the signal through elements in the loop, such as preamplifiers, power amplifiers, and demodulators. Therefore, this propagation delay is compensated for by the I and Q signals. , The phase of the signal must be matched.

In the power amplifier using the Cartesian feedback loop, the propagation delay problem of the signal generated from the modulator to the demodulator is passed between the preamplifier and the power amplifier. The propagation delay problem of the power amplifier using the Cartesian feedback loop is applied to the local input of the modulator. Compensation can be made by placing a relative difference between the phase of the carrier applied and the phase of the carrier applied to the local input of the demodulator. To this end, in the present invention, the phase of the carrier generated by the local oscillator 16 of the transmitter is arbitrarily delayed by the phase shifting device 17 to be applied to the demodulator to compensate for the propagation delay of the loop.

2 is a structural diagram of a phase shifting device using a vector modulator according to the present invention.

This phase shifter can be implemented by using a vector modulator, and has a function of adjusting the phase of the output carrier by the relative magnitude of the DC signals applied to the I and Q inputs of the vector modulator. 1].

here, cos (w _c t) Frequency w _c Is the carrier and x and y are direct current signals that adjust the phase of the carrier at the vector modulator output. As can be seen in Figure 1, x, y can be implemented by the voltage source (Vcc) and the variable resistor (21, 22), in-phase component (I) and quadrature component (Q) in the multipliers (23, 24) in the vector modulator Are multiplied by the carriers, respectively. The two signals are then added at combiner 25 and then modulated into a high frequency signal. As such, by adjusting the two variable resistors 21 and 22, the relative sign and magnitude of the x and y values can be changed to adjust the phase of the carrier obtained at the output of the vector modulator, thereby adjusting the accuracy of the phase adjustment and the range of the phase variable. Can improve.

As described above, according to the present invention, by implementing a phase shifting device used in a Cartesian feedback loop to increase power efficiency by using a vector modulator, the accuracy of phase adjustment and the range of phase variation can be widened, and the cost can be increased. There is an excellent effect that can be saved.

Claims (1)

A loop filter for maintaining stability of the in-phase component signal and the quadrature component signal to be input; A local oscillator for generating a carrier signal for modulating the input signal; A vector modulator for modulating the input signal stabilized through the loop filter at a high frequency by using a carrier signal input from the local oscillator; A high frequency power amplifier for amplifying the high frequency modulated input signal through the vector modulator to produce appropriate transmit power; A directional coupler for sampling the input signal amplified by the high frequency power amplifier; A phase shifting device for delaying a phase of a carrier signal input through the local oscillator; A vector demodulator for demodulating the input signal sampled by the directional coupler using a carrier signal delayed by the phase shifter; A power amplifying unit comprising a difference calculator configured to match and phase a demodulation signal output from the input signal and the vector demodulator; The phase shifting device includes a first multiplier for coupling a first DC signal generated by a voltage source and a variable resistor and an in-phase component signal according to a carrier signal input from a local oscillator; A second multiplier for combining a second direct current signal generated by the voltage source and the variable resistor and a quadrature component signal according to a 90 ° phase shifted signal of the carrier signal input from the local oscillator; And a combiner for coupling the outputs of the first multiplier and the second multiplier.