VCA8500BOARD: default power up mode was lose efficacy

user6022821

Part Number: VCA8500BOARD

When I used default power up mode by VCA8500, I give it a 500khz 100mv AC signal,then the signal wasn't amplified,and present a square wave.

over 5 years ago

0 Praveen Aroul over 5 years ago

TI__Mastermind 49786 points

Hello,

Welcome to TI E2E forum.

A couple of questions.
1. Do you notice the square wave on all the 8 channels? Can you attach the scope waveforms of the input and the output channels?
2. Have you tried the PC control mode to control the VCA8500 device functionality?

0 user6022821 over 5 years ago in reply to Praveen Aroul

Prodigy 40 points

1.Here is the input (yellow)and the output(purple) scope waveforms,and 8 channels are identical.

2.Yes,I have tried PC control mode, the output waveform doesn't change.

Thanks!

0 Praveen Aroul over 5 years ago in reply to user6022821

TI__Mastermind 49786 points

Hi,

Square wave occurs in cases when the signal chain gain is too high.

With 20dB fixed LNA gain, 20dB PGA gain, the signal chain gain is 40dB (assuming 0dB attenuation), this would amplify the signal amplitude by 100.

You may want to reduce the input amplitude and check.

0 user6022821 over 5 years ago in reply to Praveen Aroul

Prodigy 40 points

Hi,

I've reduce the input signal to ±20mv,but the output signal was still wrong.

The first picture is my test bed, did there something wrong?

Thanks for your reply!

0 Xiaochen (Sean)Xu over 5 years ago in reply to user6022821

TI__Expert 6040 points

in your plot, red plot shows about 250mVpp sine signal. make sure the Vcntl signal is applied correctly. 0V is min gain and 1.2V is the highest gain.

the setup has a lot of noise due to cables. we suggest you use SMA/BNC cable to minimize the coupling noise.

if you input 100mVpp, you can adjust the Vcntl to make the device out put unclampped waveforms. please note VCA8500 has clamp function on the VCA output as well. if signal is too big, the output will be clamped.

Thanks!

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VCA8500BOARD: default power up mode was lose efficacy