0 Preface The signal source is the basic electronic equipment in the fields of measurement and debugging of electronic products and technical support for military equipment. With the development of science and technology and the advancement of measurement technology, ordinary signal generators have been unable to meet the needs of production debugging in the field of electronic technology. DDS technology is an emerging direct digital frequency synthesis technology with high frequency resolution, fast frequency switching, continuous switching phase, low phase noise of output signal, programmable, all-digital easy integration, small size and light weight. Therefore, it has broad application prospects in the fields of radar and communication. 1 system design The design scheme of the full digital-controlled function signal generator using DDS as the signal generation core device proposed in this paper can be set according to the output signal waveform type, the output signal amplitude and frequency can be numerically controlled, the output frequency is wide, etc., and the American A/D company is selected. The AD9850 chip controls and processes the 32-bit frequency control word of the AD9850 through a single-chip program, and then amplifies it to a digital attenuation network with a digital potentiometer as the core, thereby realizing the full range of signal amplitude, frequency, type, and output options. digital control. The structure of the function signal generator is shown in Figure 1. The system is mainly composed of a single chip, a DDS direct frequency signal synthesizer, a digital attenuation circuit, a true RMS conversion module, an A/D conversion module, and a digital integral selection circuit. 2 The basic principles of DDS The Direct Digital Synthesizer is a frequency synthesis technique that directly synthesizes the desired waveform from the phase concept. A direct digital synthesizer typically consists of a phase accumulator, an adder, a waveform storage ROM, a D/A converter, and a low pass filter (LPF). The composition of the DDS is shown in Figure 2. Where K is the frequency control word (also called phase increment), P is the phase control word, W is the waveform control word, fc is the reference clock frequency, N is the word length of the phase accumulator, D is the ROM data bit and D/ The word length of the A converter. The phase accumulator is accumulated by the step length K under the control of the clock fc, and the output N-bit binary code is added to the phase control word P and the waveform control word W to address the waveform ROM as the address of the waveform ROM, and the waveform ROM output is output. The D-bit amplitude code S(n) is converted into a staircase wave S(t) by D/A conversion, and then smoothed by a low-pass filter to obtain a synthesized signal waveform. Since the synthesized signal waveform depends on the amplitude code stored in the waveform ROM, an arbitrary waveform can be synthesized using DDS. Capacitor Leakage Test Power Supplies The ADP series capacitor leakage test power supply is specially designed and customized for capacitor manufacturers` product quality control process or users of capacitors for capacitor ripple current durability life test.
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