The MCU used in the input and output and MCU control unit is the single-chip AT89S51. The input circuit uses rotary encoders, buttons and potentiometers. The output signal frequency and amplitude display circuit is designed by HD7279 with 8-bit frequency effective digital and 4-bit output signal. A circuit with effective amplitude display function.
The design of the signal generator and filter The signal generation circuit uses direct digital signal synthesis (DDS) technology and is implemented by the AD9834 of Analog Devices. The device has the characteristics of high precision, low power consumption, simple interface (serial), few peripheral components and complete functions. The internal phase accumulator of the device is 28 bits (that is, 2P is divided into 2 equal parts), the output frequency is (M represents the frequency control word, its range is -1), and the minimum output frequency f phase modulation register is 12 bits. Changing its initial value $ U can realize the modulation of the initial phase angle U of the output waveform (U = 2P $ U / 2 master clock f is up to 50MHz; it can generate sine wave, square wave and triangle wave.
DDS signal generator and LPF circuit are shown as in Fig. 3.
In the circuit, in order to further improve the stability of the signal generated by the DDS signal generator, the main clock of the DDS chip UF uses a 16MHz active crystal oscillator. In order to minimize the impact of the DDS chip on the power supply, the digital ground and analog ground should be designed separately, and 0.1LF ceramic decoupling capacitors should be added between the digital ground / analog ground pins of the chip and the ground line. When designing the PCB, you should increase the copper area of ​​the power supply and the ground wire as much as possible, use the ground wire to shield the high-frequency part such as the crystal oscillator, and minimize the parasitic inductance and parasitic capacitance of the signal line and the ground wire, thereby improving The anti-interference ability and stability of the circuit system.
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