A Research Of Variable Gain Power Amplifier For Microwave Drived Light Emitting Plasma

Light Emitting Plasma(LEP) is a new type of light source driven by microwave with continuous spectrum. It was born in the 90’s of last century, which has the advantages of high efficiency, energy saving, spectrum continuous approximation of natural light and the optical efficiency of up to 115-150lm/w. The novel LEP light source adapt microwave solid-state power module, which include sweep frequency source, variable gain amplification combination, coupling detection and control parts.The main purpose of this paper is to study the adjustable gain RF power amplifier, which is the fore part of variable gain amplification combination. It mainly includes pre-drive, drive and electric adjustable attenuator. It provides corresponding input signal power to end amplifier, and according to the requirements of the feedback loop adjusts the output power. The specific technical indicators are: operating bandwidth 420MHz~470MHz, the output power is greater than 30 dBm, the gain is greater than 30 dB, and the attenuation range is greater than 10 dB.This paper detailed analysis the circuit design and board map on the RF power amplifier, and discuss the design method of RF power amplifier. The ADS software is adopt to simulate the power amplifier stability, bias circuit, input and output matching circuit. In addition, small signal S parameters and large signal harmonic balance are carried out respectively. According to the working principle of electronic attenuator, performance parameters of the attenuator are simulated. Protel99 and AutoCAD2004 are used to design wiring board design and structure respectively.After the above design, the power amplifier was processed and manufactured, and the sub module debuggings were made including the power supply, pre-drive, drive and adjustable attenuator. If each module can meet the design target of the system, it is necessary to carry out the overall system test. In power supply module, there are five power supply, and a power voltage stabilizing chip is used to provide four power supply; In pre-driver module, if output power is 3W and 4W, power gain is about 15.8dB and 14.3db respectively. In the drive module, small signal gain is about 20 dB, if input power is larger than-1dbm, gain compression is more obvious. When input power increases to 3dbm, gain compression is more than 2dB and gain is about to 17.7db. In electrically tunable attenuator module, if attenuation voltage is 0V and 20 V, the attenuation value is 15.2dB and 3.0dB respectively.Finally, the overall system test results show that: in the working frequency range, if input power is 0dbm, output power is greater than 32.5dBm, gain is greater 32.5dB, and attenuation adjustment range is larger than 12.2dB. It meets the design requirements.