April 9, 2022
1、The sawtooth wave generating part of the mask
The generation of the sawtooth wave of a specific frequency is divided into two modules: one is to generate a 100KHz sawtooth waveform; the other is to generate a 30KHz sawtooth waveform.
The digital circuit can effectively reduce the influence of the characteristics of the analog device and the external ambient temperature on the generation of the sawtooth waveform. This design uses a circuit composed of NE555 timer and peripheral devices. The frequency of the generated sawtooth wave is in the range of 0 to 200kHz. Through parameter adjustment, a relatively linear and stable 100KHz sawtooth wave can be obtained. NE555 is used as a high-stability controller for precise timing pulses, and the fluctuation in the sweep frequency band range obtained after frequency modulation does not exceed 3dB, which makes the generated waveform more accurate and free of high-order harmonic components.
Pictuer 1 Sawtooth Wave
2、Voltage Controlled Oscillator Section of the shield
The voltage-controlled oscillator part is the core of this design. It is selected according to the frequency tuning range and output power, and only the downlink channel of the base station is shielded instead of the uplink channel. Voltage-controlled oscillator refers to the output frequency of the oscillator is a function of the input voltage signal. This design uses the MQE and MQW series voltage-controlled oscillators from Murata, Japan. Taking the GSM900 signal as an example, the MQE920-2079-T7 chip is used. The chip can meet higher phase noise requirements, has faster tuning speed, good frequency-temperature characteristics and frequency drift performance, good power flatness, and good electromagnetic compatibility.
Picture 2 Voltage Controlled Oscillator
3、Design of RF power amplifier module
The main function of the RF power amplifier module is to power amplify the 1800MHz signal output by the voltage-controlled oscillator. This design uses the yp242034 chip. The yp242034 chip is a high-efficiency power amplifier, covering a wide frequency range, from 1800MHz to 2.7GHz. , with high linearity, high gain and high power added efficiency and other characteristics, and integrated power detector, widely used in DCS or GPRS network. They are all automatically matched to 50Ω internally; input terminal and output terminal.