OPA4354: 放大器论坛

Steven Wen

Part Number: OPA4354
Other Parts Discussed in Thread: OPA4325, OPA365, OPA354

Why does the OPA4325 perform better than the OPA4354 when the input is below 100 mV? My circuit is attached below. The DC input is applied at pin 10, and I'm measuring the output at pin 7. As shown by the dotted line, the OPA4325 provides better linearity. Why is that?

24 天前

0 Eirwen 22 天前

TI__Mastermind 25275 points

已经收到了您的案例，调查需要些时间，感谢您的耐心等待。

0 Eirwen 21 天前回复 Eirwen

TI__Mastermind 25275 points

The main difference between the OPA4354 and OPA4325 is the Voltage output swing from rail. The OPA4354 has typical value of 100mV from the rails while OPA4325 has typical of 10mV from the rail. Hence, you are seeing non-linearity for inputs <100mV for OPA4354. We are working on a new amplifier OPA4620 which swings close to output rails. The circuit is a peak detection circuit.

What is the minimum peak that you want to detect?
What is the required speed?

We also have OPA365, which is a zero cross over, 50MHz amplifier with output swing from rail <20mV across temperatures.

0 Steven Wen 21 天前回复 Eirwen

Prodigy 10 points

In our application we need to detect signals as small as 60 mV, with a required bandwidth of about 2 MHz. Could you clarify which datasheet parameter you are referring to in your explanation? Is it the 'Voltage Output Swing from Rails'?

Also, why is the OPA4325 able to swing closer to the supply rails (≈10 mV) compared to the OPA4354 (≈100 mV)? What design or architectural difference enables this improvement?zero-crossover input stage?

Could you clarify the relationship between the zero-crossover input stage and the output voltage swing from the rails? what are the key output-stage differences between OPA365/OPA4325 and OPA4354 that lead to ≈5–10 mV vs. ≈100 mV headroom?

0 Eirwen 8 天前回复 Steven Wen

TI__Mastermind 25275 points

I am sorry for not being clear before. Yes, I was talking about 'Voltage Output Swing from Rails'. There is no relationship between the zero-crossover input stage and output voltage swing from rails. However, the key difference between the OPA365/OPA4325 and OPA354 is that OPA354 has an extra circuitry to have one of the best overload recovery time which restricts the output swing to 100mV from supply rails.

I would suggest OPA365 for its

Output swing closer to rails that enables detection of 60mV
It has sufficient bandwidth
Good DC precision enabling less offset error at output.
Zero cross over enabling Wider input range without cross over distortion.
Low bias current for peak detectors.

0 Steven Wen 6 天前回复 Eirwen

Prodigy 10 points

Thanks for the reply. since OPA365 did not drop-in for OPA4354(old design) Could we use the OPA4325 instead of OPA4354?

I am not very clear about this parameter 'Voltage Output Swing from Rails'. how to simluate this parameter? Are there key design trade offs ? that influence why some OPA can swiing closer to rails~10mV like OPA4324 but like OPA4354 ~100mV?

0 Eirwen 5 天前回复 Steven Wen

TI__Mastermind 25275 points

OPA4325 is a lower bandwidth device with 5V/us slew rate. For peak detection, high slew rate and bandwidth is required. What is the fastest frequency of the input?

As mentioned before, we are releasing OPA4620 which is drop in for OPA4354 and will be the right fit.