What Is a Linear Amplifier?

The non-linear distortion of the RF power amplifier will cause it to generate new frequency components. For example, for the second-order distortion, it will generate the second harmonic and two-tone beat frequency, and for the third-order distortion, it will generate the third harmonic and multi-tone beat frequency. If these new frequency components fall within the passband, they will cause direct interference to the transmitted signal, and if they fall outside the passband, they will interfere with the signals of other channels. To this end, the RF power amplifier needs to be linearized, which can better solve the problem of signal spectrum regeneration.

Linear amplifier

The non-linear distortion of the RF power amplifier will cause it to generate new frequency components. For example, for the second-order distortion, it will generate the second harmonic and two-tone beat frequency, and for the third-order distortion, it will generate the third harmonic and multi-tone beat frequency. If these new frequency components fall within the passband, they will cause direct interference to the transmitted signal, and if they fall outside the passband, they will interfere with the signals of other channels. To this end, the RF power amplifier needs to be linearized, which can better solve the problem of signal spectrum regeneration.

Chinese name

Linear amplifier

Foreign name

linear amplifier

Brief introduction

Standard nuclear instrument plug-in

gain

5 750 times continuously adjustable

linear amplifier

Linear amplifier IC is an indispensable part of various electronic products. How to design high-quality electronic products, in addition to requiring the best overall solution, whether the amplifier design is reasonable and reliable directly affects the system performance of the entire electronic product.

This instrument is a standard nuclear instrument plug-in. It is inserted into the FH0001 plug-in chassis. It is mainly used to shape and amplify the output signals of scintillation detectors, proportional counter tubes, fission chambers and semiconductor detectors. In addition to its characteristics, it also has better linearity and stability. Therefore, it is a new NIM plug-in that replaces the above two amplifiers.

1. Magnification: 5 750 times continuously adjustable.

2. Long-term stability of magnification: 0.1%.

3 Magnification temperature stability: 0.02% / .

4 Integral nonlinearity: 0.2%.

5. Input-referred noise: 10V.

6. Overload: 200 times overload, recover to 2% of baseline at 2.5 times non-overload pulse width.

7. Input polarity: positive or negative. Output polarity: Positive output impedance 50.

8. Forming time constant: 0, 0.5, 1, 2, 3, 4, 5, 6 S.

9. The instrument can work normally when the relative humidity is 90% (30 ° C).

10 Transportation test: Under the condition that the acceleration is (1 to 1.2) x 9.8m / s2 and the frequency is 20 to 40 Hz, the transportation simulation test should work normally after 8 hours.

Temperature range: 0 50

Relative humidity: 90% (at 40 ° C)

Power supply: ± 24V, 30mA, ± 12V, 10mA, 2W

The non-linear distortion of the RF power amplifier will cause it to generate new frequency components. For example, for the second-order distortion, it will generate the second harmonic and two-tone beat frequency; for the third-order distortion, it will generate the third harmonic and multi-tone beat frequency. If these new frequency components fall within the passband, they will cause direct interference to the transmitted signal, and if they fall outside the passband, they will interfere with the signals of other channels. To this end, the RF power amplifier needs to be linearized, which can better solve the problem of signal spectrum regeneration. The principle and method of the basic linearization technology of the RF power amplifier is nothing more than taking the amplitude and phase of the envelope of the input RF signal as a reference, comparing it with the output signal, and then generating an appropriate correction. There are three commonly used techniques for linearizing RF power amplifiers: power backoff, predistortion, and feedforward.

The criterion for judging non-linearity and linearity can be: use a fixed frequency f1 and level input for the amplifier, observe the output of the amplifier, if its output contains additional frequency components (generally its harmonics 2f1, 3f1 ...) The amplifier is then non-linear.

In practice, the linear / non-linear region of any amplifier depends on the input signal level. When the input signal level is greater than a certain value (P1dB), the output nonlinear frequency component will increase sharply. In order to reduce non-linear products, the input signal is generally required to be 3 ~ 6dB lower than the amplifier P1dB.

There is also a problem with the signal modulation method. For example, the PAR (peak / mean) of a GMSK-modulated signal has a low linearity requirement on the amplifier, because the signal does not exceed the P1dB point and pushes the amplifier into the saturation region. QPSP's PAR = 6 ~ 10dB, its amplifier has higher linear requirements, otherwise the signal can easily exceed the P1dB point and push the amplifier into the saturation region. OQPSK has a lower peak value than QPSK, so the power amplifier used by CDMA mobile phones does not have to be completely linear.

In fact, the most fundamental explanation of this problem is to read the book of low-frequency and high-frequency electronic circuits. The amplification curve of the tribasic tube is linearly amplified only at the lower section of the operating point. When the operating point is raised, it enters the nonlinear amplification interval. Usually class A and B power amplifiers work in the linear section, but the starting efficiency is very low, usually only 30% to 40%. Most of the energy is consumed by the internal resistance of the electrode and the flow angle is large; Class-A amplifiers work in a non-linear region with high efficiency, which can reach 70% to 80%, but the waveform of the output amplified signal will be distorted, which will generate harmonic components. Therefore, Class-C amplifiers must be connected in the LC oscillation circuit. Because the LC oscillation circuit can play a certain filtering role, filter some harmonic components and retain the fundamental component.

Therefore, if you use a constant-inclusive modulation method, you can use a non-linear amplifier; if you use a non-constant-inclusive modulation method, especially when the peak average is relatively large, you must use a linear method.