A Digital Tester For Frequency Response Characteristic Base On The High Performance DDS Chip AD9954

The digital tester for frequency response characteristic, which is also called frequency-sweeping instrument, plays a very important role in modern electronic measurement. It can be used to measure the amplitude-frequency characteristic and phase-frequency characteristic of the unknown network, and give the real-time the transmission-characteristic measurement of the unknown network. The traditional analog frequency-sweeping instrument, which mostly uses the LC circuit as the frequency oscillator, is more expensive, too much bigger and heavy to carry. It can only display the curve of amplitude-frequency, but can't used to measure the phase-frequency, and can't used to print the curve of frequency response characteristic either. It brings many discommodity to the user.In the paper, the digital tester for frequency response characteristic based on the high performance DDS chip AD9954 is presented. The signal generator of sweep frequency is based on DDS device AD9954,the signal measuring circuit is based on gain and phase detector AD8302,the real-time control and deal circuit is based on TMS320VC5409,and the periphery interface circuit is based on AT89S52.The system can generate sweep frequency signal with the frequency range from 100KHz to 150MHz, and with the power range from -45dBm to +18dBm.It can measure the gain and phase of the network, display the measure data by liquid crystal displayed and print it by the printer. Digital and miniaturization be fulfilled in the design of the frequency characteristic. Cost for the instrument. The instrument provides many kinds of periphery interface, make it very convenient to use.