# How do you connect the pins of a Photomultiplier Tube (PMT) to an Analog to Digital Converter (ADC)?

I am using a Photomultiplier Tube (PMT) and trying to send a signal to a computer. The PMTs use a voltage and output an analog signal (continuous electrical signal) which cannot be read by a computer. I am planning on using a 16-Bit Analog to Digital Converter (ADC) to convert the analog signal of the PMT to a digital signal which a computer can read.

The problem is that I can't seem to figure how to attach the wires soldered to the output pins of the PMT and the input of the ADC. What color of wires do I need to achieve this task? And what wires should be attached to what pins to get the best results. If possible, please write what the pins on the ADC mean so I can research on this more, if there is no answer. Please provide schematics or sources if you have a potential answer to this question.

• I assembled a 70-IC tic-tac-toe machine using shiny tinned wires and slip-on transparent insulating sleeving. Thus the color of the wires...does not matter. The ADC should have VIN pin, where the analog input voltage enters to become a quantized measurement. Some ADCs have VREF pins, so you need to study the choices of reference voltages. And the timing of the start-conversion activity may require a trigger; likely you'll need an analog-comparator to trip on the PMT output, and the digital output should promptly start the ADC activity. – analogsystemsrf Jun 6 '18 at 3:35

It depends on how many photons you want to count. There are three modes:

Source: Hamamatsu PMT Handbook

If you want to observe lots of photons (not counting) then a transimpedance preamplifier will work just fine. The result is a current, you convert it to a voltage with the transimpedance amplifier, (and maybe add a lowpass filter to reduce noise) and measure the voltage with an ADC. The ammount of light is determined by back-calculating the current from the voltage, and if you know the current, the PMT's datasheet should tell you relation of incident light on the PMT's active area.

In the figure below, b) is for measuring pulses.

You can also count photons if you have a high speed pulse counter and a comparator (convert to a voltage, then set a voltage level for true=I found a photon and false= I didn't see one). However, if there are too many photons they start stacking together as a voltage and this circuit wont work.

You can do hybrids of these circuits, I built a circuit with a transimpedance amplifier and a comparator. (after the current is amplified to a voltage, you could also build both a counting circuit and ADC).

A transimpedance amplifier looks like this:

The resistance simply converts a current to a votlage with this relation:

$V = I*R_{gain}$

so if your PMT is has a max detection level of 1mA of current, and you have a resistance of 5k, this will equal 5V of most ADC's

Source: Hamamatsu PMT Handbook

The problem is that I can't seem to figure how to attach the wires soldered to the output pins of the PMT and the input of the ADC. What color of wires do I need to achieve this task?

Usually PMT's also come with a base, which could include a resistive divider and/or a high voltage power supply. For a PMT to be operational, it needs a high voltage supply and a resistive divider to step down the voltage at each dynode. Some PMTS make you supply the high voltage and include the resistive divider in the base, some don't have either. A decent multimeter should be able to find which pins are the resistive dividers. You would also need to find the pin that is the anode. The dynodes should have all similar resistances and the input pin should be the pin with the highest resistance between any two pins (if you have a base with resistors in it. The anode is the one you connect to an amp, make sure if you don't know what your doing you use a protection circuit on the amplifier as a high voltage could easily burn out your circuitry.

Source: Wikipedia PMT's

Remember to have fun! Hook the preamp up to a fast (1GHz) oscilloscope and put it in a very dark room, you can see the individual photons hitting the PMT, which is very cool.

A photomultiplier is really an electron multiplier and it produces a current. Various schemes are used to read the current from voltage across a load resistor to sensitive current amplifiers.

Because it is based on electron flow, the high voltage is negative with respect to ground, as electrons flow from negative to positive. PMTs require testing and adjusting voltage for the best response and precautions to avoid light while they are powered.

DO you just have a tube and socket? Or a socket with voltage divider resistors? This is a good source of information https://www.hamamatsu.com/resources/pdf/etd/PMT_handbook_v3aE.pdf