TFG2900A Series Function/Arbitrary Waveform Generator Users’ Guide
Suin Instruments Co., Ltd
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2.2 Working principle
2.2.1 Digital combination
: To generate a voltage signal, traditional analog generator uses electron
components to constitute oscillator. While its disadvantages are low frequency accuracy and
stability, complex technology, low resolution, not convenient for setting the frequency and
programming by the computer. DDS is a digital way of signal generating. It has no oscillator and
uses digit combination to generator a serial of data flow, and then generates an analog signal
through the D/A (digital analog converter).
For example, to generate a Sine, you should firstly make Y=SinX digital quantification, and then
store X as address and Y as quantification data to waveform memory one by one. DDS uses phase
accumulation technology to control the waveform memory’s address. In each sampling clock
period, it accumulates the phase increment to the real time value of the phase accumulator.
Through changing phase increment to change DDS output frequency value. According to the
address phase accumulator outputs, waveform memory gets out waveform’s quantification data,
and then converts to analog voltage through D/A and operational amplifier. Waveform data is
discontinuous sampling data, what DDS generator outputs is a staircase sine waveform. Higher
harmonic in the waveform has to be filtered by low pass filter (LPF), after that the outputs is
continuous sine wave.
2.2.2 Working principle
: There is a high resolution digital analog converter(D/A) inside device,
which uses high accuracy reference voltage source to provide reference voltage which can be set
for amplitude and offset control, thus we guarantee output amplitude’s and DC offset’s accuracy
and stability.
After amplitude and offset controlling, the signals will go through attenuator, voltage amplifier
and power amplifier, and then be output by output interface.
Microcontroller (ADSP) controls keyboard and displaying, when the keys are pressing, it will
recognize the code and then execute it. The display circuit will display instrument’s working status
and various parameters.
The knob in the front panel is used for changing the number in cursor position. Every rotating to
an angle there will be a trigger pulse generating. Controller can judge whether it is left or right
rotating, if it is left rotating, the number in cursor position will be decreased one; if it is right
rotating, the number will increase one, and carry or borrow a bit continuously.
