MMIC POWER AMPLIFIER THESIS

MMIC POWER AMPLIFIER THESIS

The DPD coeffi- cients are optimized for each value of xmax and for each nonlinearity measure see 4. Higher gate resistance leads to lower gain for a power FET device. The low 3rd harmonic power values are due to a low-pass filter matching network at the output of the pHEMT amplifier—if a two-tone signal was the input to the PA and the third-order intermodulation IM3 was measured, an increase in the range of 10 dB to 20 dB would be expected. There- fore the voltage at the load RL is purely sinusoidal with amplitude vd1. For a typical biasing path with gate and drain biases varying proportionally to the input power red thick line there is only 1. AET 7—12V yields the highest gain.

In this case, the maximum average output power that could be obtained with dynamic biasing was 1. There is a 4. EVM, distortion power and average power gain are recorded for all of these cases. Mmic power amplifier thesis Resistor R2 makes it possible to adjust the gain. For a typical biasing path with gate and drain biases varying proportionally to the input power red thick line there is only 1.

The transistor is biased in class A condition at maximum envelope amplitude, i.

As expected, E0 and Eyx yielded almost exactly the same results. Another possibility would be to have the gate bias depend on the input signal to the PA, that is the predistorted signal, while the drain bias depends on the power of the modulated signal. The other scenario is auxiliary envelope tracking AETdescribed in Section 5.

mmic power amplifier thesis

Thus another important difference with ET is that the drain bias does not follow the envelope down to the lowest levels. For the specific case of the Saleh model with continuous gate and drain variation the class-A and -B biased transistor yielded 3. This will unfortunately lead to re- duced transconductance and increased capacitance, resulting in further gain diminishment. The chapter begins by explaining the automated measurement setup, and the modifications to the optimization method from Chapter 4.

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Varying the gate linearly with the input power in combination with AET can be almost as effective as quadratic variation, having the advantage of reduced computational or circuit complexity and reduced bias bandwidth, since the square of the input power need not be computed.

Though the efficiency at high and low amplitudes may be degraded, the average efficiency can be maximized for any signal [48]. The preference for a set of bias functions over another is based on the variable being optimized i. The drain tracker design was challenging because of the difficulties involved in the drain bias current measurement. A maximum gain of The average gain is relative to class-A gain.

For the HBT, the optimization was carried out from simulation data as de- scribed in Section 4. These considerations imply that the selection of an appropriate load, and of the biasing functions are dependent on the device, and of course on the appli- cation.

Mmic power amplifier thesis

It is important to clarify that it is solely with illustrative or explanatory pur- poses that gain or phase responses are used. For the chance of pursuing this PhD am I most grateful to Mikael Gidlund, who encouraged me to apply, was a good reference, and a good supervisor and guide while I was finishing my master thesis in Sweden.

The improvement respect to the static biased class-AB is of 1. This case illustrated how the selection of the bias function can result in a trade-off between efficiency and output power, and showed that the resistive load can be adjusted to the biasing functions to obtain the desired voltage swing for maximum output power.

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Dynamic gate biasing can add amlifier tenths of a dB in gain, while ET had some tenths of a decibel less gain than the static biasing case. The measurements where taken for an average output power values of 28, 29 and 30 dBm. For example, Nemati et al.

In FETs, channel current can be increased by increasing the gate width. It requires no additional hardware, since the algorithms are imple- mented in a digital signal processor or FPGA unit [55].

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mmic power amplifier thesis

A case study of dynamic biasing Table 3. Nevertheless, the bandwidth of the bias signal at the drain is still of concern.

Though the technique is attractive because of the poaer efficiency inherent to switching amplifiers, it is very sensible to time misalignment between the bias and the RF signal, and to distortions in the bias signal due to imperfect envelope amplification i. The baseband signal was root-raised-cosine filtered with a roll-off ammplifier of 0.

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For a typical biasing path with gate and drain biases varying proportionally to the input power red thick line there is only 1. Ideally, taking a single-tone input power sweep for varying gate bias could help us see how the PA would react to bias current increase at peak input power, but the temperature increase due to higher dissipated power would limit the output power capability of the device.

A typical Doherty amplification system [1]. Though dynamic gate in- creases the drain bias current near compression, it does not diminish PAE noticeably.

When the RF signal is large in bandwidth, the high frequency components will be distorted due to the limited frequency response of the envelope amplifier. Measurement of different device technologies Table 5. If DPD is combined with ET, the bias source will have to track the envelope of the predistorted signal which has much higher bandwidth, thus setting a very high demand on the bandwidth of the envelope amplifier.

It will soon be shown that varying the bias with respect to power drives the amplifier into class-AB mode, even if the starting point is a class-A amplifier.

mmic power amplifier thesis