THS7530-Q1: Saturation behavior

Hello Giora,

Let me move this to the high-speed amplifiers forum, they should be able to help you.

Regards,
Karl

Giora,
Can you please provide a detailed schematic of your circuit? Are you testing it on your own PCB or are you using the TI Evaluation Module? What quiescent current are you measuring?

-Samir

Samir,

I am using my own PCB.

The schematic is like: Figure 19. AC-Coupled Single-Ended Input With AC-Coupled Differential Output on page 13

of the THS7530 data sheet. The differences are:

1. The 24.9 ohm resistors are 0 ohms and no 33p cap.

2. The outputs are terminated by 51 ohm resistors.

3. The current in DC was ~ 40ma

Giora

Giora,
I will have to try this on the EVM to confirm what I am seeing. Can you please send me:

1. Scope shots of what you are seeing at the output when changing the gain in saturation.

2. What gain voltages you are setting.

3. What your clamp voltages are.

-Samir

Samir,

1. I do not have a scope picture but I add a drawing of the output pulse shape when in saturation. (see below).

2. Gain was minimal.

3. No clamp voltage - pins are open.

Hello Giora,
I tried this on an EVM and do observe the same phenomena that you are seeing. Unfortunately this is a very old device and the designer no longer works at TI. I spoke to some other designers about it and they believe that the overdriven output signal and the gain control block are interacting with each other when the amplifier outputs are saturated. Unfortunately this phenomena is unavoidable for this particular amplifier structure.

-Samir

Hello Samir,

Thanks for your help.

Giora