1. Basic principles of design: Reasonable design of voltage dividers is crucial for the correct use of photomultiplier tubes. Improper voltage dividers can cause changes in the resolution, linearity, and stability of the tubes. The design of the voltage divider should be considered based on the requirements for the photomultiplier tube, such as optimal signal-to-noise ratio, high gain, and high current output. The voltage divider of a photomultiplier tube can be divided into three parts: the front stage (cathode first multiplier), the middle stage, and the final stage,



(1) Cathode - First multiplier. It is important to maintain an appropriately high electric field between the cathode and the first multiplier. The distribution of the front stage voltage is determined by the electron collection efficiency, the first multiplier secondary electron emission coefficient, time characteristics, and signal-to-noise ratio. The front stage voltage of photomultiplier tubes used in energy spectrum analysis is determined by parameters such as pulse amplitude resolution or noise.
(2) The voltage of the intermediate stage multiplier can be selected according to the desired gain. In some cases, it is desired to reduce the gain of the transistor without changing the total voltage. A simple method is to adjust the potential between the intermediate multiplier poles to achieve (which is applicable within a certain range). The intermediate multiplier poles generally use a uniform voltage divider, but for focusing structures (linear focusing structures), the voltage between the first few multiplier poles still has a significant impact on parameters such as pulse amplitude resolution and time characteristics, and should be carefully selected.
(3) The final stage multiplier voltage divider is determined by the output linearity. In some applications (such as high-energy physics), there is a strong pulse signal output. In order to reduce the space charge effect, the voltage applied to the last few multiplier electrodes and anodes with high charge density should be appropriately increased, and the voltage gradient of the last few multiplier electrodes and anodes should be increased. Based on this consideration, a conical voltage divider is generally used. In order to avoid affecting the potential distribution of the multiplier due to excessive signal pulse current in the last few multiplier poles, it is often necessary to connect coupling capacitors (pulse signal type voltage dividers) to the last few multiplier poles. The capacitance value depends on the output charge. If the linearity requirement is better than 10%, the capacitance value should reach at least 100 times the output charge of each pulse,

2. Universal voltage divider



(1) DC output type



(2) Pulse signal type



Connect the coupling capacitor to the last few multiplier electrodes, and during the pulse period, supplement the charge of the photomultiplier tube to suppress the decrease in the final multiplier and anode voltage, greatly improving the pulse linearity.
(3) Time based


3. Typical voltage dividers are divided into high linear (high current) output voltage dividers, voltage dividers that reduce oscillation, and gain controllable voltage dividers. High linear (high current) output voltage dividers include incremental (conical) voltage dividers, voltage regulator voltage dividers, unidirectional multiplier voltage dividers, and transistor voltage dividers. The voltage dividers with controllable gain include (taking measures) short circuiting the multiplier and anode, and adjusting the potential of the multiplier.

1) High linearity (high current) output voltage divider circuit

(1) Incremental (conical) voltage divider

(2) Voltage regulator and voltage divider.

By switching the voltage divider resistor to a Zener diode in both the front-end and back-end stages, regardless of the voltage applied between the cathode and anode, the electrode voltage can be maintained at a constant level, ensuring stable operation of the photomultiplier tube and achieving maximum output linearity.

(3) Unidirectional multiplier voltage divider.

The unidirectional multiplier voltage divider is connected in series with a capacitor at each contact, which is a voltage divider with both power supply and high output linearity

(4) Transistor voltage divider.

In scintillation counting applications, output linearity issues often occur when photomultiplier tubes are used for high counting. In this situation, transistors can be used instead of voltage divider resistors. This linear decrease in output caused by the resistance of the voltage divider can be improved. It is recommended to use this method to test high counting rate in the near detector of the dual detector carbon oxygen ratio spectroscopy logging instrument.

2) In a fast (below 10ns) stress field, the voltage divider that reduces oscillation can be reduced by connecting the damping resistors Rn+1 and Rn+2 to the final second stage multiplier pole, with a resistance value of 10-100 Ω,



3) The output control of a photomultiplier tube in a gain controllable voltage divider circuit is usually achieved by changing the applied voltage. But sometimes it is not desired to change the high voltage, and in situations where the gain of the tube is high and the working voltage is low, due to the low multiplier voltage, the collection efficiency and secondary emission coefficient will decrease. In this case, the following two methods can be used.

(1) Short circuit the multiplier pole to the anode. This is actually reducing the number of doubling poles to control gain, and can increase the inter pole voltage and signal-to-noise ratio. It can be output from the anode or multiplier.



(2) Adjust the intermediate multiplier potential. Add an adjustable resistor (potentiometer) to the intermediate multiplier, adjust the voltage of the intermediate multiplier, and control the gain of the photomultiplier tube. The experiment shows that it is effective to adjust the gain of the photomultiplier tube by only changing the voltage of the intermediate multiplier electrode while keeping the space potential of the front stage constant.