I need help figuring out how an evaluation board for an op amp works

Question

What I am trying to do: I have a special photo detector(nano-wire, operates at very low temp) that creates an output trigger pulse every time it detects a photon. This trigger pulse(see picture attached) is 20-25ns wide and about 500mV in amplitude. We need to use this pulse to trigger more than one electronics in our set up but unfortunately the amplitude is too low to be able to do that. We are expecting that we will be recording photons at the rate between 1Hz-5kHz. So the trigger that this detector will produce will be irregular instead of a continuous stream. So for that purpose it was suggested that I use an operational amplifier as a comparator. I will feed the trigger from the detector into the comparator and once the pulse goes higher than a set reference(that I will provide) then the comparator will produce a signal higher in amplitude and I can use that as my trigger. So, I bought an op amp chip from analogue devices and also an evaluation board.

The thing I need help with : I don't know how to use the eval board and I have many questions including,

1. Where does the my opamp chip go? I purchased it separately. However it seems like there is already a chip attached in here.
2. How do I make the connections? Will I put in the trigger into the IN+ port and ground the IN-?
3. I thought I would have only one output but there are two output ports here.
4. On the left side, there are ports labeled Vcc and VTT, and on the side of these ports are tiny loops that are labeled VTT TP14 and VCCTP11. What are they for and what do these labels mean?
5. Then there is a SMA port 'LE-HYS'. What is that? Do I have to use all these extra ports?

Any help to get me started would be appreciated.

The eval board I am referring to : [1]: https://i.stack.imgur.com/NdmXN.jpg

Answer 1

You are using an ADCMP609 comparator. This is almost certainly not fast enough. Your pulse width in is 20 - 25 nsec, but the risetime on a 609 output is rated at 25 to 50 nsec. If you provide a 25 nsec input pulse, it's entirely possible that your output will only be partway through its change in output level before it drops again. This is called a runt pulse, and is not very useful. Furthermore, you state that your detector output is 500 mV, but you don't say what load it can drive. Your evaluation board has termination resistors on the inputs, almost certainly 50 ohms. Can your detector drive a 50-ohm load?

Before you do anything else, download the data sheet for the ADCMP609. Start studying it and ask someone for help. It's pretty clear you have no idea how your board works.

You will also need to track down the data sheet for the evaluation board. I recommend contacting Analog Devices.

Where does the my opamp chip go? I purchased it separately. However it seems like there is already a chip attached in here.

Your board does indeed have the chip already installed. Congratulations. You now have a spare chip.

How do I make the connections? Will I put in the trigger into the IN+ port and ground the IN-?

Connect your detector to the INP+ connector. Connect a variable DC voltage of about 250 mV to the INP- connector. Make sure both SMA connectors have their shield tied to ground.

I thought I would have only one output but there are two output ports here.

Yes. The ADCMP has complementary outputs. When one is high, the other is low. You REALLY NEED to look at the data sheet.

On the left side, there are ports labeled Vcc and VTT, and on the side of these ports are tiny loops that are labeled VTT TP14 and VCCTP11. What are they for and what do these labels mean?

The little loops are test points. You can grab them with a scope probe to monitor them while the circuit is operating. VCC and VTT are voltages which supply the chip. What voltages?

VTT should be tied to ground.

You REALLY REALLY NEED to look at the data sheet.

Then there is a SMA port 'LE-HYS'. What is that? Do I have to use all these extra ports?

Please. Read the data sheet.

Answer 2

Based on the photo, you have an evaluation board for a specific comparator, which would seem to be appropriate for your application, as described (perhaps not in input impedance).

Normally I would expect to find a datasheet for the board at least showing a schematic and Bill of Materials, however the AD page is not very helpful as of this writing.

You should contact AD and request the information on the evaluation board itself, part number
EVAL-ADCMP609BRMZ.

As to using another part, it would have to involve adapting the board to a different part, which may not be compatible pinout, and some fairly delicate soldering and probably hacking. You would want to have full data on the board and both parts.

Answer 3

1. Where does the my opamp chip go? I purchased it separately. However it seems like there is already a chip attached in here.

The board in your picture already has an ADCMP609BRMZ comparator IC installed.

2. How do I make the connections? Will I put in the trigger into the IN+ port and ground the IN-?

Yes, your signals go into IN+ and IN-.

3. I thought I would have only one output but there are two output ports here.

It's a comparator, so it provides logic signals at its outputs. Here is a description of each pin taken from the datasheet

The chip provides both Q and /Q signals for convenience -- you are free to use either one or both.

On the left side, there are ports labeled Vcc and VTT, and on the side of these ports are tiny loops that are labeled VTT TP14 and VCCTP11. What are they for and what do these labels mean?

"TP" stands for test point -- it's just a place where you can attach a probe -- oscilloscope or multimeter.

Vcc is your supply voltage to the comparator (see the link above to the datasheet). VTT is a conductive plane embedded in the PCB to which you can apply a termination voltage of your choosing. It is used in conjunction with properly terminating your input signals. This comparator is meant to be used with high-speed signals, and so the way they are terminated is important. More information may be found in this article:

https://www.marvintest.com/KnowledgeBase/KBArticle.aspx?ID=196

The use of the VTT plane is optional.

5. Then there is a SMA port 'LE-HYS'. What is that? Do I have to use all these extra ports?

It's used to program the comparator's hysteresis. Full details may be found in the datasheet.

Answer 4

It is not an Op Amp but rather a uncompensated comparator with high gain at 60MHz.

The convenient hysteresis input allows remote voltage control hysteresis if one wishes to estimate amplitude from pulse width after calibrating the impulse response with various thresholds and hysteresis levels using an integrate and dump circuit on the output pulse. However that feature is limited by overdrive levels above around 25 mV as the prop delay rises below this rapidly.