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PGA855: The recommend triple waveform frequency in test and measurement EE.

Rannie Zhou
Intellectual 1400 points
Part Number: PGA855
Other Parts Discussed in Thread: PSPICE-FOR-TI, TINA-TI

Tool/software:

Hi team,

My customer wants to use PGA855 in the DGT loop to sense the triangle wave signal. 

If the Sine wave is to be measured, the frequency of the triangle wave should be controlled at about 40KHz. 

If you are measuring a ramp wave or a triangle wave, and you want to ensure the linearity of the PGA855 output, what is the frequency of the triangle wave that is most suitable for this amplifier?

Best regards,

Rannie

  • 0
    TI__Intellectual 1400 points

    Hi team,

    I also attached the BD for your reference. The previous stage is a DAC with the output of 10kHz (maximum), ±1V triple waveform. The DAC sample rate is 1us, 100uV. 

    So that's why customer wonder the suitable frequency with the input of triple waveform to ensure the linearity of the PGA855 output.

    Best regards,

    Rannie

  • 0 in reply to Rannie Zhou
    TI__Guru 51036 points

    Hi Rannie,

    An ideal pure triangle wave is not bandlimited, and its frequency spectrum consists of the fundamental, and an infinite number of odd harmonics.  Nevertheless, the higher harmonics roll-off proportionally to the inverse square of the harmonic number, therefore, most of the energy of the waveform can be captured within the few first harmonics.  Therefore, for a practical circuit implementation, limiting the bandwidth to the first few harmonics of the fundamental may be acceptable.

    The PGA855 offers a typical f(-3dB) bandwidth of 10-MHz (without external filters).  If the fundamental of the triangle wave is 10kHz, the device will have more than enough bandwidth to reproduce, the 3rd, 5th, 7th and 9th harmonic without issue. 

    The PGA855 TINA-TI or PSPICE-for-TI model  can be used to simulate the frequency response and slew-rate of the PGA855; so you can tune the circuit for your application needs using simulation.

    Can you define what is meant by "to ensure linearity of the PGA855 output"?  Can you quantify this requirement? Is there a % error specification that needs to be met?

    Thank you and Regards,

    Luis