OPA1S2384: op-amp selection

Hello Hale,

I will get an update to this thread to you by the end of the day today in Arizona.  

I believe I have the key information I need to recommended a few devices; does your customer have any priority preference for any of the following features?

- integrated switches/switching

- Low Vos and Vos drift

- Rail-to-rail inputs and/or outputs

- Higher slew rate

- Lower noise

I did notice your input impedance of 100 Ohms request; most of our high-speed amplifiers will have high-impedance inputs relative to the rest of the circuit.  Is there a particular signal standard or first stage circuit I should be aware of when making a recommendation?

Best,

Alec

Alec,

The customer requirement is included sample and hold function. And the other requirement is as above:

3.3V supply,
input signal differential swing 550mV
Bandwidth 80Mhz
Input signal impedance 100ohm

Please help make sure whether OPA1S2384  is the best option

Alec

Alec Saebeler said:

Is there a particular signal standard or first stage circuit I should be aware of when making a recommendation?

No specific signal. Just follow above requirement is enough.

Hello Hale,

The OPA1S2384 remains an option for your customer.  I also have seen prior support on projects for sample & hold with the OPA860 and OPA615:

OPA860: OPA860 sample& hold circuit - Amplifiers forum - Amplifiers - TI E2E support forums

I do have an older document which details the sample & hold circuit design & implementation process, but we would use either the OPA860 or OPA1S2384 in place of the older amplifiers within the article:

https://www.ti.com/lit/an/snoa603/snoa603.pdf

I will take another look later today once I have a break from projects & meetings.  At the moment I believe you have a good product selection for the design.

Best,

Alec

Hello Hale,

I did miss the S&H section in the OPA1S2384 datasheet.  We have the OPA1S2385 which has inverted logic for the internal switch compared to the OPA1S2384.

Either of these parts would appear to be good recommendations for your customer's system.

If I may ask, which customer are you supporting here on this project?

Best,

Alec

Alec,

So the option is opa860, OPA1S2384 and OPA1S2385. Could you help make comparison and show the differences?

This requirement is from Sourcephotonics which is the optical module supplier. And it's also my first time to know this kind of requirement.  It's pre-research.

Hello Hale,

I will compose a comparison for you.  Together we can help support the customer and work towards design-in and WIN.

Best,

Alec

Hi Alec,

Please help provide the comparison with us. Thanks.

Hello Hale,

I will provide the comparison by end of day today.  I apologize for any delay.

Best,

Alec

Hello Hale,

Please find my comparison below:

sample_and_hold_comparison.xlsx

The key differences between OPA1S2384/5 and OPA860/1 are here:

- OPA860/1 are OTA, or operational transconductance amplifiers.  They are primarily intended for laser drivers and transimpedance applications, but can be used in S&H circuits.

- OPA1S2384/5 are nearly identical devices, with the only difference being whether the internal switch is active HIGH or active LOW.

- OPA1S2384/5 are also designed for transimpedance applications, but have an entire detailed section in the datasheet supporting sample & hold applications.

Best,

Alec

Hi Alec,

The customer want to use OPA1S2384 devices. But we have a little confused about this device.

1. What's the SC control signal voltage? How long does it take from 0V to high level logic voltage? Can GPIO give the signal toSC?

2.Could you help provide the close loop gain bandwidth when gain is 10?

In below picture, the bandwidth is 90Mhz

And in below picture, the bandwidth is 10Mhz

What's the condition differences? And the customer need 40hz, what's the typical gain bandwidth when gain =10?

Hi Alec,

So *if the customer application is no capacitance load, the GBWP is 10MHz and it can't meet their requirement. Is that right?

Hello Hale,

Is the customer requirement 40Hz or 40MHz?  The OPA1S2384 can likely be used unless the bandwidth required is in excess of the available bandwidth in a gain of 10V/V.

Please confirm the operating frequency and bandwidth for the customer circuit.  Please also confirm the required gain (10V/V?) and if the customer would be willing to use a gain stage prior to the OPA1S2834 if the bandwidth is not sufficient for all of the gain to be on the S&H stage.

Best,

Alec

Hi Alec,

Thanks for your explanation about SC signal.

And about the 90Mhz bandwidth in capacitive load application and 10Mhz bandwidth in fig 6, I am still confused. Because if we add capacity load to the op-amp, it will reduce the bandwidth. But from current datasheet, it seems that capacity load enhance the bandwidth. It's weird. Please help check about the bandwidth issue in below condition. I am still confused about the differences.

Hi Alec,

Could you help share the phase frequency, amplitude frequency graph in different capacity load and resistor load with me?