Handling Instruction - PeakTech 4055 Handbuch

3.2. Working principle of DDS
* To generate a voltage signal, the traditional analogue 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 technique, 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 analogue signal is generated from digital-
analogue 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-analogue converter. Based on the amplitude value preset by user, it
generates a corresponding analogue 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.
3.3. 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.

4. Handling instruction

4.1. General operation rule
4.1.1. Data input
* If an item is selected, the parameter value can be entered by ten numeric keys writing from left to right. If
there are more than one decimal point entered in a parameter, only the first one is valid. For the function
of "Offset", minus can be entered. To make the data come into effect, unit key must be entered after data
input. For wrong data input, there are two ways to modify. If the output end permits wrong output signal,
press any unit key to end and then re-enter data. If the output end does not permit wrong output signal, re-
select the same item and enter correct data, and then press unit key to end it.
* The input of data can use any assorted decimal point and unit, but the generator will display it in fixed
format. For example, the data 1.5kHz or 1500Hz entered will be effective displayed as 1.500.00kHz.
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