VCA822: Low Pass filter

Andrea Fontana1

Prodigy 210 points

Part Number: VCA822
Other Parts Discussed in Thread: TINA-TI

Hello,

I'm using VCA822 into an AGC system in the configuration of Gmax = 10 (Rf = 1K, Rg =200) from a single-ended source.

VCA822 has quite big bandwidth (> 100MHz), and i need to filter out all the signal components up to 125 KHz.

I was thinking to realise the low-pass filter by adding a capacitor, let's call it Cg, in parallel to Rg.

Have you the formula that allow me to calculate the proper value of Cg ?

Or, eventually, can you suggest (if any) an alternative method ?

Thanks in advance

Andrea

over 4 years ago

0 kai klaas69 over 4 years ago

Guru 140200 points

Hi Andrea,

why not running a simulation with the TINA-TI reference design?

VCA822 TINA-TI Reference Design (Rev. B)

Kai

+1 Michael Steffes over 4 years ago

Guru 48395 points

Morning Andrea,

The VCA822 input stage is two buffers turning your input voltage into a current for the multiplier core - that current then goes through a CFA output amplifier configured as transimpedance to get back to voltage - these are all very fast stages so filtering towards the input will not bandlimite the noise of later stages. Perhaps best to add a filter after the output as either a simple RC or perhaps an active filter stage with another amplifier.

0 kai klaas69 over 4 years ago in reply to Michael Steffes

Guru 140200 points

And running the TINA-TI simulation will give a big surprise

Kai

0 Andrea Fontana1 over 4 years ago in reply to kai klaas69

Prodigy 210 points

Found the surprise !

Thanks

0 kai klaas69 over 4 years ago in reply to Andrea Fontana1

Guru 140200 points

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VCA822: Low Pass filter

VCA822 TINA-TI Reference Design (Rev. B)