NE592 video amplifier

[PbFoot]

Hi,

I am working on a circuit to sense very small infrared pulses. I am using a TAOS TSL267 for a sensor. It's a got the PIN diode and transimpedance amp in one device. I am using four of those summed together. Then, I want to pass the signal to a NE592 video amp to bump up weak signals. I will be configuring the amp as single sided instead of differential input.

I am looking at the NE592 datasheet, but I am very new to this type of a device. Looking at some of the example circuits, I am trying to figure out exactly how to get the signal into the 592 so it will be happy.

In the attached image, what are the 51 ohm resistors on the left side (the inputs) for? I know it's a basic question, so please pardon my ignorance.

[GK]

They are just there to terminate the input signal into ~50 ohms. When sending (just for example) high frequency signals over a length of coax, the receiving end needs to be properly terminated.

The 51 ohm resistor on the unused input could be omitted (pin just shorted to ground) with very little effect on quiescent DC balance, which isn't of any consequence as the output signal(s) are ac coupled.

This part is essentially the same as the long obsolete uA733. There are plenty of cheap high speed op-amps available that would do the job just as well (since you don’t need differential inputs anyway). Any particular reason for picking this part? Or do you need differential outputs?

[PbFoot]

Thanks for the info! I only chose the 592 because it seemed like it would be good for receiving fast pulses, and I saw it used in some designs that are similar in application to mine. I don't need differential inputs or outputs. I plan to output to a 74121, and then into a microcontroller. I have some AD620 on hand. Maybe those would be better?

Any advice you can offer on a good choice for a single sided amp would be greatly appreciated.

Thanks!

-PbFoot

[GK]

Since you intend to trigger a monostable (74**121) what you really need is some form of threshold detector. Your best bet would be a comparator IC with a logic level output that can drive the trigger input of the monostable directly. How fast (duration) are your pulses? Perhaps even something basic like an LM311 with a logic-level pull-up resistor would be adequate.

I don’t have the time right now to look up the datasheet for your IR receiver, but depending on its gain and signal output level you may not even require a signal gain stage in the middle.