controlling waveform attenuation on 5412

[Chilango]

Hi,

I was wondering if there was any way to specify the attenuation from signal outputed from the High or low gain amplifier in the 5412 using the VI attribute NIFGEN_ATTR_POST_AMPLIFIER_ATTENUATION.  I tried using the setViAttribute function to control the post amlifier value but got an error.  It is my understanding that NIFGEN sets the post and pre values based on the gain/amplitude setting (say from configureStandardWaveForm) and probably includes the gain of the high/low gain opamps in figuiring what these values should be?  Is it expected that the user should control these pre/post attenuation settings or are they specifically meant for "only" the driver.

I imaginge that if I wanted a particular amplitude I would need to know the gain of the high/low opamps in the output path (which is fixed and not documented anywhere) in order to be able to configure these settings?

Thanks

[kirsch]

Hello Chilango,

The NI-FGEN driver selects the internal attenuators and gain amplifiers based on the value of NIFGEN_ATTR_ARB_GAIN (or NIFGEN_ATTR_FUNC_AMPLITUDE if you're in Function Mode). Since all analog components have part-to-part variations, NI-FGEN also fine adjusts the gain using a high precision DAC. The adjustment is based on the characterization of the hardware done during calibration and stored on the device's EEPROM.

The NIFGEN_ATTR_POST_AMPLIFIER_ATTENUATION is in the NI-FGEN API so that it can be used during external calibration and not during the normal usage of the device. If you are not performing external calibration, then use NIFGEN_ATTR_ARB_GAIN or NIFGEN_ATTR_FUNC_AMPLITUDE to get the desired output voltage.

Marcos (regiomontano)

[Chilango]

Hi Kirsch,

Just for clarification, the NIFGEN_ATTR_POST_AMPLIFIER_ATTENUATION and NIFGEN_ATTR_PRE_AMPLIFIER_ATTENUATION settings for the pre/post Amp attenuator blocks in the output path are different for different amplitude/gain settings....correct?  Meaning if I select 5.5V or 4.3V the driver would write different values for these settings?  That's the way I'm interpretting it, you just mentioned that they can be used during calibration so I wasn't sure if that was the only time they where changed.

I'm rewriting some tests that used a different scope that had post-output attentuation control.  It seems that the attenuators in the 5412 are configured internally by the driver (via the amplitude/gain settings) so changing the value of the amplitude and measuring via an external device in effect tests the 5412 attenuators.

[kirsch]

That's correct, the driver will select the attenuation settings based on the Gain/Amplitude chosen by the user.

If you want to verify which attenuators were selected by NI-FGEN for the current Gain/Amplitude, then you can read the NIFGEN_ATTR_POST_AMPLIFIER_ATTENUATION or NIFGEN_ATTR_PRE_AMPLIFIER_ATTENUATION (using NI-FGEN 2.4 and newer,  but not with previous versions).

Marcos