RF power amplifiers to achieve real-time detection

Radio and television transmitter is an integrated electronic system, which includes not only the wireless transmitter audio channels, but also the detection and control circuit channel, so in the design, it must ensure that wireless access in addition to the technical specifications in the normal range sampling must also be designed advanced alarm detection and protection circuitry to ensure that the transmitter is working to achieve the transmitters online automatic monitoring and control. In recent years, high-power solid-state TV Transmitter with multi-power synthesis technology development, more and more manufacturers to adopt a modular structure design, so a single power amplifier module is a transmitter of Ji Bence Dan Yuan Zheng Ge, this would Zhuozhongtaolun Detection of a single module and control circuitry to achieve the transmitters online automatic monitoring.

I. Work

In the power amplifier module, the main parameters for the detection and control of the supply voltage, the amplification of the operating current, output power, reflected power, over temperature and over-excitation protection, Figure 1 for the detection and control functions to achieve the above block diagram, which consists of sample to enlarge circuit, V / F conversion, isolation circuit, F / V transformation, A / D conversion, AT89C51, display circuit and output protection circuits and other components.

RF power amplifiers to achieve real-time detection

1, isolated circuit

In the power amplifier module, due to the application of high-power device, often a single module's output power than the larger, and therefore there is a big small-signal high-frequency disturbances such as not handled properly, will affect the ADC circuit after the class work resulting in inaccurate test data, display data beat phenomenon, and even malfunctions. Optocoupler used here to isolate, as optocoupler with small size, long life, wide operating temperature range, anti-jamming performance, the non-contact and input and output are completely isolated in the electrical characteristics, which will simulate the circuit and digital circuits completely isolated to protect the system in the high-voltage, high power radiation safe work environment.

2, LM331 voltage frequency converter

V / F transform and F / V transform with integrated block LM331, LM331 NS company of U.S. high performance and low cost integrated chips, used for precision frequency-voltage conversion Used. LM331 adopted a new temperature compensation bandgap reference circuit, the entire operating temperature range and low to 4.0V power supply has a high accuracy. At the same time it wide dynamic range up to 100dB; good linearity, the maximum nonlinear distortion is less than 0.01%, low frequency 0.1Hz good linear fashion; transformation of high precision, digital resolution of up to 12 ; external circuit is simple, just a few external components can access convenient form V / F or F / V converter and so on, and easy conversion to ensure accuracy.

Formed by the LM331 voltage frequency converter, LM331 comparator within the input, timing comparator, R-S flip-flop, output drive, multiple zero transistor bandgap reference circuit and the current switching components. Open collector output driver tube used, and thus the current through the selection logic and external resistance, flexibility to change the logic level output pulse to fit TTL, DTL and CMOS logic circuits such as different.

When the input Vi + input of a positive voltage, the input comparator output is high, so R-S flip-flop set, the output high, output drive tube conduction, f0 output logic low, while power supply Vcc also on the capacitor C2 through resistor R2 charge. When the charging voltage across capacitor C2 is greater than Vcc to 2 / 3, the comparator outputs a high time to make R-S flip-flop reset, output low, output drive tube cut-off, a logic high output power f0 level, the same time, complex zero transistor, capacitor C2 quickly through the complex zero-discharge transistor; electronic switch to discharge capacitor C3 to the resistance R3. When the capacitor C3 discharge voltage is equal to the input voltage Vi, the input comparator output is high again, so that R-S flip-flop set, such a repeated cycle, constitute a self-excited oscillation. F0 output pulse frequency is proportional to the input voltage Vi, to achieve a voltage - Frequency transformation. The input voltage and output frequency relationship: fo = (Vin × R4) / (2.09 × R3 × R2 × C2) by the resistance of the equation, R2, R3, R4, and C2 directly affect the conversion result of f0, and therefore the precision components certain requirements must be properly selected based on conversion accuracy. Resistor R1 and capacitor C1 form a low pass filter can reduce the interference of the input voltage pulse, helping improve the conversion accuracy.

Similarly, the LM331 can also constitute a frequency - voltage converter circuit.

3, data processing circuit

Data processing circuits including A / D digital-analog converter ADC0809, AT89C51 microcontroller and display circuit and other components. ADC0809 is a CMOS process using eight-channel single chip made of eight A / D successive approximation converter, successive approximation converter including a comparator, a number of analog conversion controller, a successive approximation register (SAR) and a logic control unit, the conversion of successive approximation is based on the variational principle be completed by the control logic unit, which is simple, easy to implement, no delays. AT89C51 is a high-performance 8-bit microcontroller, on-chip with 4k bytes of FLASH erasable programmable read only memory, the instruction set compatible with MCS-51, which can easily control the application of a variety of fields. In the design, P0 port as a data port, P1 port as a digital input output control, P2 as the display module and the ADC0809 the address control lines, INT0 interrupt input terminal for the keyboard, thus forming a simple measurement system microcontroller.

After LM331 F / V transformed voltage signal sent to digital-analog converter ADC0809, AT89C51 microcontroller reads the digital-analog converted real-time data, calculated by internal software, the results sent to the screen display, display mainly The amplifier tube current, supply voltage, output power and reflected power and so on. Enter the amount of detectable signal by the photoelectric switch directly after isolation of the P1 port into the AT89C51. Display circuit using 16 × 2 character dot matrix liquid crystal display module, the display module has a built-in 192 characters (5 × 7 點 font), indicating strong functions and can form various kinds of input, display and shift mode and other functions, and with MCS-51 series MCU interface is simple, and simple software programming features.

Second, software design

Block diagram of the basic structure of the software 3. Main program loop collection is mainly analog and switch signals, and calculated according to signal type, from the value sent to LCD display, while under the control requirements, the output control signals to realize the power amplifier module control, alarm and protection.

RF power amplifiers to achieve real-time detection

Keyboard interrupt subroutine is mainly used for view display, set some parameters such as alarm and RS232 communication baud rate and so on. RS232 communication aimed at a single power amplifier module to send data to the whole control unit, the total machine control module for processing and display, in order to achieve the remote control and server connections.

3, Conclusion

This article describes the power amplifier module detection control unit, because of high power and high magnetic field applications of radiation, so the key is to solve the signal acquisition and transmission of high frequency interference and the input and output circuits of the isolation measures, while the number of waves on the software also demanding.