TIDA-01187: Schemati Review of TIDA-01187 based design, using THS4541 as single ended output

Hello Shyam,

I understand you want to operate the circuit above 450MHz and utilize more of the THS4541 bandwidth.  There are a few considerations:

1. Use a more wide-band transformer, such as WBC1-1TL (750MHz)

2. Create an output network to load the THS4541 and also provide desired impedance to TLV3601 (such as a pi attenuator network, etc).  As long as both outputs of the FDA see the same impedance, you can create a load circuit to go single-ended.

3. Use an op-amp to go differential-to-single-ended after the output of the THS4541 FDA.

Best,

Alec

Dear Alec,

Thanks for responding

I wish not to expand BW on higher side but operate in Lower BW also

Currently the transformer cuts down the signal less than 8MHz or heavily attenuates

I wish to remove it and take the THS Output directly to comparator

1. What should be VCM in this case

2. How can i take Vout+ of THS safely to TLV3601

3. How to still properly maintain or terminate or balance the Vout- of THS ?

4. Can you draw the load network that you are suggesting in the attached simulation file or hand draw it for my understanding.

OPA857+THS4541+TLV3601_WITH_LOS(1).TSC

5.Also on other side suggest a diff-single ended converter opamp

Hello Shyam,

Okay thank you for the details.

How low in frequency do you need?  What is the highest frequency you need to pass without attenuation?

1. VOCM should be set to midsupply on the FDA, which in this case is still 1.65V.  You can also float the pin.

2. We would need either 1) transformer, 2) diff to single-ended op amp, 3) output load to match Vout+ to TLV3601

3. The transformer or balun helps with this; without one of these two devices we would need to load the outputs Vout+ and Vout - equally, and not connect Vout- to the rest of the signal chain.

4. I can work on a file for you; this option of an output network is the most likely to cause distortion or phase delay issues.  Using a transformer/balun with required frequency range or an op-amp would be better options.

5. If you need to go up to 450MHz with an op-amp as a buffer, your options include OPA356, OPA856, and LMH6629 for low-voltage supplies.  We also have high-bandwidth op-amps for supply voltages > 10V.

You may also consider if you need an FDA at all, if you are going differential to single-ended you could just choose a high performance op-amp.  It depends on your overall system requirements.

Best,

Alec

1. Frequency Requirement : 0-100MHz

2. I understood T/F is not a right option for requirement stated in No.1

3. OPA356 seems correct fit to me, correct me if i am wrong, what i need is a single supply op-amp and differential to single ended conversion
(i will pick a sample and try to place it in my current board to quickly see the performance)

Let me know if OPA356 is suitable, how i need to configure same

Hello Shyam,

You can proceed with trying OPA356.  I will find a good reference circuit for you on this topic. 

Best,

Alec

A Gentle Reminder, can you please throw some light on configuration of OPA356 as Diff to Single ended converter