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AWG7102: Scale and Amplitude

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cyklucifer
Posts: 2
Joined: September 13th, 2014, 6:03 am

AWG7102: Scale and Amplitude

Post by cyklucifer » October 31st, 2014, 9:11 am

I searched almost everywhere but did not get the answer I want: what is actually the scale functionality and the adjustment of the peak to peak amplitude doing in the AWG.

Can I understand the scale is just an internal analog signal amplification? or it scale the uploaded signal by some factor and then quantize them again? The rear case, huge distortion is introduced in the signal.

What about the Vpp that can be configured for every channel. Does this also related to quantization problem?

Hope get answers soon.

Thanks

Carl M
Tektronix Applications
Tektronix Applications
Posts: 797
Joined: July 30th, 2008, 4:45 pm
Country: United States

Re: AWG7102: Scale and Amplitude

Post by Carl M » November 13th, 2014, 5:09 pm

the awg5000 and awg7000 series operate very similarly so the following can be applied to 14-bit, 10-bit, and 8-bit modes.

the native data format is the AWG setup file. It is a single container for setup, all user waveform vectors, one main sequence, and (if available) all sub-sequences. waveform vectors can be in single precision float format (4 bytes per sample, 1 byte for marker vectors) called Real, or integer format with proprietary bit masking (2 bytes per sample, includes marker vectors) called Integer. bit and byte definitions are detailed further in the AWG Series Programmer Manual. http://www.tek.com/node/832085

Integer format is 1:1 with the digital DAC values. Aside from the proprietary bit masking, this is straight forward.

Real format is normalized from +1.0 to -1.0. After pressing the RUN button (which is the sequencer, it is always used internally even when you are in continuous or triggered run modes) the waveform is converted into the digital DAC values and moved from the PC memory to sequencer memory.

Waveform vectors in the Integer format are more efficient both in storage and transfer into the sequencer. Why use Real format? depending on your use case, it can be convenient. For the AWG7000 which can dynamically shift between 8-bit and 10-bit modes, using Real format ensures that you can actually use the extra precision after enabling 10-bit mode. With Integer format if you did not program your vectors for 10 bit mode, you will not receive the extra precision. Also if you perform waveform math operations, Real waveforms will be performed as floating point prior to digitization and type-conversion losses are minimized.

You may have now noticed that waveform vectors are not voltage samples. They are unit-less digitizing levels. The AWG output settings for amplitude and offset are what scale the digitizing levels into a voltage. For example: 0.5 Vpp amplitude, 0 V offset, and a Real sample value of -0.75 should result in a voltage of:

voltage = amplitude / 2 * Real Value + offset = -0.1875 volts

of course, this is a design specification. Just because we told it to output -0.1875 volts doesn't mean that it's this value. You'll need to cross reference the DC output accuracy specification for your awg from the Performance Verification and Specifications for that detail http://www.tek.com/node/869814

Also note that you can configure the awg display to show the digital dac values or the scaled voltages from the interface. View > Display Properties > Waveform Window Tab > Table > Analog or Digital (with binary or hex sub options for digital). Analog is scaled based on the amplitude setting. Digital displays the internal DAC value.

Hopefully you find this as fascinating as I do but I never expect our customers to have this kind of deep architectural knowledge. I'm much more interested in results. Could you briefly explain what you are trying to do? I could provide topical suggestions rather than overarching theory.
Tektronix Application Engineer

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