OPA657: Gain-Bandwidth Product of OPA657 in datasheet

JeongRok Gim

Part Number: OPA657
Other Parts Discussed in Thread: OPA818

Hi, I'm using the OPA657 as transimpedance amplifier(TIA), and also reading datasheet of OPA657.

I find it states 'OPA657 has 1.6GHz Gain-Bandwidth Product(GBWP)' and also figures open loop gain graph (magnitude and phase).

I think there are two poles in graph (between 100Hz and 1GHz), maybe 500kHz and 200MHz or 300MHz.

Anyway I have question about GBWP. This graph has intercept at 800MHz (when magnitude=0dB).

This specification doesn't match with 1.6GHz GBWP.

How can I interpret this?

Thanks.

over 1 year ago

JeongRok Gim over 1 year ago

Prodigy 50 points

OPA657's open loop gain graph I saw is here.

Michael Steffes over 1 year ago in reply to JeongRok Gim

Guru 48395 points

The GBP definition, and what you need for TIA design, is the single pole projection to 0dB. Get that by going to the Aol=40dB point and multiplying that frequency by 100X, 1.59GHz here,

This recent article tries to explain this confusion, and also some bad information in the industry.

https://www.planetanalog.com/why-is-amplifier-gbp-so-confusing-insight-12/

Also, the OPA657 has been upgraded by the OPA818.

And this useful TIA design presentation we did way back in the 2002 time frame and used to be on the TI website, one of several TechDay presentations we did back then,

7446.Transimpedance design flow using high speed op amps.pptx

JeongRok Gim over 1 year ago in reply to Michael Steffes

Prodigy 50 points

Thanks for your kind explain. This helps me to understand about GBWP.

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OPA657: Gain-Bandwidth Product of OPA657 in datasheet