VCA2615: Different Non-Linear performance between chip to chip

Jenn Kim

Part Number: VCA2615

Hi,

I have been observing that the linearity performance (Power Input vs. Gain/IM3) of the VCA2615 chip behaves different between different chip.

Some of them were way worse than the others in which, the gain curve was not flat at all and had bad linearity before the compression point.

For our application, we have

Single-ended input to the LNP
LNP Gain set to 22dB
Gain Amplifier set to High Gain Mode

I started swapping VCA2615 chip with the new one on our PCB and saw that the linearity was completely different between the parts.

Also, I have noticed that most of the chips had non-linear performance at control voltage < 1V.

I was wondering if this is normal?

Do these VCA2615 chip have different performance (i.e., Linearity Performance - Gain and IM3) between chip to chip?

over 2 years ago

0 Bellala Kalyan over 2 years ago

TI__Intellectual 1590 points

Hi,

Thanks for reaching out to us. We're checking the production data of VCA2615 across different lots to learn about variability of device. Please let us review the data and get back to you.

Regards,

Kalyan

0 Bellala Kalyan over 2 years ago

TI__Intellectual 1590 points

Hi,

We looked at our production data. Only channel to channel gain matching is constrained to +/- 0.33 dB as mentioned in datasheet but device to device gain matching can be upto +/- 2.5 dB. So, what you're observing is expected.

Regards,

Kalyan

0 kai klaas69 over 2 years ago

Guru 140200 points

Hi Jenn,

as it cannot be seen from your description, I want to say that one major mistake with these VGA chips is to override the input stage with a too high signal.

Kai

0 Jenn Kim over 2 years ago in reply to Bellala Kalyan

Prodigy 10 points

Hi Bellala,

Are you also saying that the IM3 can be different between device to device?

Also, I see that in the DS, test condition was normally done with load resistance of 500ohms to GND.

How high of load resistance can I connect without causing distortion?

0 Bellala Kalyan over 2 years ago in reply to Jenn Kim

TI__Intellectual 1590 points

Hi Jenn,

Can you please elaborate what you mean by IM3 ? is it like third harmonic distortion HD3 ? or Intermodulation spur (IMD3) ?

Regards,

Kalyan

0 Jenn Kim over 2 years ago in reply to Bellala Kalyan

Prodigy 10 points

Hi Bellala,

I am referring to IMD3

Jenn

0 Bellala Kalyan over 2 years ago in reply to Jenn Kim

TI__Intellectual 1590 points

Hi Jenn,

We can't really comment on IMD3 as we don't have any production data or characterization data. Regarding your question related to load resistance, you can increase the load up to 100 ohm.

Regards,

Kalyan

0 Jenn Kim over 2 years ago in reply to Bellala Kalyan

Prodigy 10 points

Hi Bellala,

Would you possibly have some data from design group regarding IMD3 that you could comment from?

I would like to know IMD3 along with variation between devices.

Thank you!
Jenn

0 Bellala Kalyan over 2 years ago

TI__Intellectual 1590 points

Hi Jenn,

We have characterization data across devices for HD3, third harmonic distortion. IMD3 can be computed from HD3. We can share you the distribution plot but we can't post it on public forum. Please drop a message to support_us_afe_tx@list.ti.com where we can share you IMD3 calculations, all the required data and support directly.

Regards,

Kalyan

0 Jenn Kim over 2 years ago in reply to Bellala Kalyan

Prodigy 10 points

Hi Bellala,

Thank you for this!

I have sent an email for direct support.

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VCA2615: Different Non-Linear performance between chip to chip