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Design and manufacture of sine wave signal source based on MP430 control

Posted by: Yoyokuo 2022-10-15 Comments Off on Design and manufacture of sine wave signal source based on MP430 control

This system takes MSP430 as the control core to design and make a sine wave and pulse wave signal source. This experiment is divided into four modules, namely keyboard scanning module, sine wave generation module, pulse wave generation module and liquid crystal Display module. In the sine generation part, the DDS chip AD9851 is used to generate a sine wave with controllable frequency. In the practical test, the amplitude of the sine wave output from the AD9851 will change with the frequency. Finally, the amplitude error is significantly reduced through software programming.

This system takes MSP430 as the control core to design and make a sine wave and pulse wave signal source. This experiment is divided into four modules, namely keyboard scanning module, sine wave generation module, pulse wave generation module and liquid crystal display module. In the sine generation part, the DDS chip AD9851 is used to generate a sine wave with controllable frequency. In the practical test, the amplitude of the sine wave output from the AD9851 will change with the frequency. Finally, the amplitude error is significantly reduced through software programming. The pulse generation part uses Verilog programming to generate a pulse wave with adjustable duty cycle inside the FPGA, which solves the instability of the pulse wave generated by turning the sine wave into a square wave and sending it to the FPGA. The system works reliably and stably, and fulfills the requirements of the basic part and the play part well.

I. Overall programme

This system requires to design a signal source that can generate positive wave and pulse wave under the condition of given ±15V power supply voltage. The signal frequency is 20Hz~20kHz, and the frequency can be adjusted step by step (step size is 5Hz), and the duty cycle of the pulse wave can be adjusted step by step between 2% and 98% (step size 2%). The amplitude is required to be adjustable in steps from 100mv to 3V (the step size is 100mv), and the performance is required to be good (high frequency stability, small nonlinear distortion, etc.), and the scheme is considered as follows:

Sine wave generation

Option 1: Using a monolithic function signal generator (such as 8038), the 8038 can generate sine waves at the same time. Pulse wave, the method is simple and easy to implement, the output of the D/A converter is used to change the modulation voltage, and the frequency can be adjusted numerically, but the step size is difficult to meet the requirements, and the frequency stability is not high.

Scheme 2: Using a phase-locked frequency synthesizer and using a phase-locked loop to lock the output frequency of the voltage-controlled oscillator (vco) at the required frequency, this scheme has good performance, but it is difficult to meet the requirements of the output frequency coverage factor, and The circuit is complex and is not suitable for generating low frequency signals.

Scheme 3: Using the direct digital frequency synthesis chip AB9851, it is very convenient to generate sine waves and pulse waves. DDS is especially suitable for occasions with low frequency, wide frequency bandwidth, high frequency stability and accuracy, and complex waveforms.

pulse wave generation

Scheme 1: The voltage corresponding to the duty cycle is generated by the D/A converter, and the square wave of the required duty cycle can be obtained by comparing it with the sinusoidal signal. However, this method has poor accuracy, and it is difficult to achieve the step requirement of 2%.

Option 2: First transform the sine wave into a sawtooth wave or a triangular wave, and then compare. In this way, although the accuracy can be improved, the circuit is complex, the cost is high, and debugging is difficult.

Scheme 3: Using the counting timing method, first convert the sine wave into a square wave and send it to the FPGA, and then use its rising edge to trigger a timing circuit, which outputs a high level during the timing period and a low level after the timing is terminated. , so that the duty cycle of the pulse wave can be adjusted step by step, and the duty cycle is transmitted from the microcontroller to the FPGA. The two modules constituted by this scheme have influence, resulting in unstable signal source.

Scheme 4: Under the control of the microcontroller MSP430, the controllable duty cycle pulse wave is directly generated in the FPGA through software programming, which is relatively easy to implement and the signal source is very stable.

Based on the above analysis, the following options are selected:

(1) The sine wave is realized by using DDS chip AD9851 to generate the program dynamically.

(2) Generation of square wave The square wave is generated inside the FPGA by programming.

The principle block diagram of the signal source system is shown in the figure:

Design and manufacture of sine wave signal source based on MP430 control
Figure 1 Overall block diagram of the system

The Links:   SKD60-16 SKIIP31NAB12T16