Based On Orthogonal DDS SSB Modulation Amplitude Frequency Characteristics Of The Design Of The Analyze

Frequency characteristic test instrument is to point to in the frequency domain measurement on a frequency response of two-port network instrument, often referred to as frequency sweep instrument, instrument is a kind of evaluation of network characteristics, occupies an important position in the electronic measuring instrument. Frequency sweep meter of’ high-end products at home and abroad high measurement precision, wide frequency range, everything is very good, but its high price and maintenance costs, and prevent this kind of product promotion in colleges and universities. Low frequency band of frequency sweep meter products is less, and mostly in traditional measurement technology, product accuracy and stability is not high, so the high performance low cost low and middle frequency sweep meter has great demand in the market.Mainstream of sweep frequency source is direct digital frequency synthesis (DDS) and phase-locked loop frequency synthesis or phase-locked loop (PLL) and direct digital frequency synthesis (DDS+PLL) hybrid scheme. Advantages and disadvantages based on the analysis of these solutions is proposed on the basis of orthogonal SSB modulation scheme for synthesis of frequency sweep signal. The scheme through the spectrum of the linear moving, will generate the DDS chip 100 hz-100 MHZ frequency signal directly on the frequency conversion to 100 m-300 MHZ, makes the frequency sweep.source output frequency range of 100 hz～300 MHZ. The circuit of the output frequency sweep signal frequency precision, both retained the excellent DDS frequency resolution and stability, and realized the function of wideband frequency sweep.Another research paper is amplitude detection circuit, the circuit adopts the gain AD8302 detection chip as the core, through optimizing the analog input channel, ensure the AD8302 at low frequency and high frequency can obtain higher measurement accuracy.The whole system adopts STM32F429 as the host controller, using RA8875 as LCD drive, on the basis of embedded graphics rendering library STemWin developed friendly human-computer interaction interface design.