Other Parts Discussed in Thread: OPA1662
Greetings.
I ran into a problem in trying to generate a sine wave with my PGA970EVM. In any mode, for any waveform generation settings, the actual frequency of the generated signal is almost two times lower. For example, for settings on image 1 (20kHz set on GUI), the real frequerency is 10.9 kHz.
I`ve found the root of the problem: In my PGA970 real update rate of the DAC is about 532 kHz, instead of 1MHz. You can see this on my oscilloscope, on image 2 (Settings of this waveform are on image 1).
Due to the discrepancy between the real and the set frequency, PGA970 incorrectly measures the signal amplitude when the frequency is set above 10 kHz (above 5 kHz real frequency). You can see it on images 1 and 3. S1P and S1N connected directly to P1A and P2A, jumpers J1, J4 closed, J2 and J7 tied between pins 2 and 3 (OPA1662 are bypassed). So, the measured signal must be the same as generated (an it is on image 3), but on frequencies above 10kHz (5kHz real) i`ve getting results like on image1. But 5kHz is too low frequency for my LVDT sensor, I need 15-20kHz.
Oh, and also maximum Gain on both ADC1 and 2 doesn`t work. When i set Gain to 1.33 and 1.67, everything is OK, but on Gain 2 i`ve getting the same results, as on Gain 1.
So, my questions are:
1. Was the DAC update rate in PGA970 changed from 1 Mhz to a lower frequency by Texas Instruments? Or it`s a bug in my PGA970?
2. Is there any way to change DAC update rate in PGA970? To set it to correct 1 MHz? Or it`as absolutely impossible, and my PGA970 hopelessly damaged?
3. And what about Gain 2x of ADC? It`s also bug, or it was disabled by Texas Instruments?
Image 1
Image 2
Image 3
