THS4531: Requirement of transformer at the input of amplifier

Shifali N

Expert 2040 points

Part Number: THS4531

Hi,

I am using THS4531IDGKR in my design. In the evaluation kit of the part I see a transformer at the input. what is the use of transformer. As the datasheet states that transformer are used to convert differential signals to single ended. My input signal will be differential. Even in this scenario is the transformer necessary. Or is it only needed if the input is single ended and to convert it into differential.

over 2 years ago

0 kai klaas69 over 2 years ago

Guru 140200 points

Hi Shifali,

the EVM does not contain an input transformer:

Kai

0 Shifali N over 2 years ago in reply to kai klaas69

Expert 2040 points

Hi,

I checked for the evaluation schematics and transformers are provided at both input and output section.(T1 at the input side) Not sure if its mounted on the board.

Is transformer only used to convert single ended input to differential? Or is there any other use case. Also why is the transformer present at the output.

0 kai klaas69 over 2 years ago in reply to Shifali N

Guru 140200 points

Hi Shifali,

the advantage of the transformer is that input and output windings are galvanically isolated against each other and that they can freely float to each other. By this you can very easily overcome DC bias voltage differencies and suppress common mode noise.

Kai

0 Shifali N over 2 years ago in reply to kai klaas69

Expert 2040 points

Hi Kai,

Hence its not required for single ended to differential conversion or vice versa as mentioned in datasheet. Is my understanding correct

0 Michael Steffes over 2 years ago in reply to Shifali N

Guru 47535 points

That is a pretty comprehensive schematic to test lots of different things - the Baluns make it easy to due network analyzer measurements but are not generally required when you are doing simple single to diff design - If you need AC coupling, blocking caps work as well. The basic idea is to check all your DC operating points first on the I/O nodes - make sure they are ok, then your AC response.

0 SimaJalaleddine over 2 years ago in reply to Shifali N

TI__Mastermind 22360 points

Hello Shifali,

The input transformer is not populated on the board, there are instead two 0 ohm resistors. We install transformers on the input of our EVMs for our differential amplifiers for testing. Most test equipment is single-ended so to check the high-frequency performance (transformers don’t work at DC and low frequencies) of our device in the lab with differential inputs we install a transformer. Similarly on the output of the FDA we install transformers because people generally have access to single-ended test equipment such as Oscilloscopes, Spectrum Analyzers and Network Analyzers. To ease testing of our amplifier at high-frequencies we install the output transformer. In the final application where the ADC has differential inputs no transformer is needed.

Thank you,
Sima

0 Shifali N over 2 years ago in reply to SimaJalaleddine

Expert 2040 points

Thanks for your reply.

Amplifiers

Amplifiers forum

THS4531: Requirement of transformer at the input of amplifier