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waveform memorizer. DDS uses phase adding technique to control the address of waveform
memorizer. Add a phase increment on the present result of phase accumulator in each sampling
clock period so as to change the output frequency value by change phase increment. According
to the address from the phase accumulator, take the quantized data out from the wave
memorizer and then convert it into analog voltage via digit-analog converter and operation
amplifier. Since the waveform data are discontinuous sampling, stair sine waveform is output
from DDS generator. The included high-level harmonic wave should be filtered by lowpass
filter so to output a continuous sine wave. With high accurate reference voltage source in digit-
analog converter, the output waveform is if high amplitude accuracy and stability.
Amplitude controller is a digit-analog converter. Based on the amplitude value preset by
user, it generates a corresponding analog voltage and then multiplied by the output signal so to
guarantee the amplitude of output signal to be the preset value. Offset controller is a digit-
analog converter. Based on the offset value preset by user, it generates a corresponding analog
voltage and then added with the output signal so to guarantee the offset of output signal to be
the preset value. The synthesized signal from amplitude and offset controllers is amplified by
the power amplifier and then is output from output end A.
2.3 Working principle of operation control
MPU controls keyboard and display parts by interface circuit. When the key is pressed,
MPU identifies the code of pressed key and then executes the corresponding commands.
Display circuit displays the working state and parameters of the generator using menu
characters.
The knob on the panel can be used to change the number in the position of cursor. A
trigger pulse will be generated for each rotating of 15°. MPU can judge whether the rotation is
left or right. If it is left, the number in the position of cursor will be subtracted by 1; if it is right,
the number in the position of cursor will be added by 1 with continuous carry or borrow.
Chapter 3 Handling instruction
General operation rule
Frequency of channel A
Frequency of channel B
Frequency sweeping
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