PeakTech 4035 Bedienungsanleitung Seite 71

4.1. Principle frame
Keyboard
Digital circuit
Amplitude
control
and AM
Offset setting
DDS
4 .2 Working principle of DDS
To generate a voltage signal, the traditional analog signal source adopts electronic components as oscillator
in different ways. So both frequency accuracy and stability are not high enough. Besides, it is of the
disadvantages of complicated technics, low resolution and inconvenient frequency setting and realization of
computer control. Direct Digital Synthesize(DDS) technique is a new developing method of generating
signals without any oscillator components, by which a series of data stream are generated using digital
synthesizing method and then a pre-established analog signal is generated from digital-analog converter.
To generate a sine signal, for example, the function of y＝sinx should be digitally quantized first, and then
taking x as the address and y as the quantized data to store them into 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
Displayer
器 器
MCU
DDS
s
Lowpas
Voltage
Power
amplification
amplification
Amplitude
Lowpass
control
Knob
Clock
Comparator
Output
attenuation
20-60dB
Output
Output A
protection
Power
amplification
-70-
Modulation
input
FM
TTL output
Output B