A121: Hybrid charge sensitive preamplifier-discriminator. Company advantage inventory.

A101 Preamplifier/Discriminator

A111 Preamplifier/Discriminator

ModelA121 is a hybrid charge sensitive preamplifier-discriminator designed for fast pulses

Microchannel plate, channel electron multiplier, count mode for low gain photomultiplier

tubes, proportional counters and solid state detectors.

feature:

?Fixed dead time

?Sensitivity: 5 x 104 electrons (voltage

? Adjustable)

? Frequency: 12 MHz periodic

?Analog monitor output

? Output pulse: min. 35 ns (adjustable)

?Vs = +5 to +7 VDC (25 mW)

?Input noise: 15 x 10-16 coulombs RMS;

? 9,650 e-RMS;_19% of threshold

? Noise Slope: 1.8 x 10-17 Coulombs RMS/pF

Notes on A121

1. PIN 1, enter

The DC level at pin 1 is 1.2 volts. This DC level must not be changed by external circuitry. Pin 1 should be AC coupled to

Detector. High voltage coupling capacitors should have adequate voltage ratings to prevent breakdown

This could damage the A121.

For detectors with anodes at ground potential:

• An anode at ground potential requires a DC path to ground to maintain a fixed potential. Can be provided by DC

Coupled to the input of the A121, it will keep the anode around 1.2 V. Alternatively, you can do AC coupling, but use

The higher value resistor (1 MEG) is grounded on the anode side of the capacitor.

2. The protection of A121 can be as follows:

3. PIN 3, threshold adjustment

The threshold of the A121 can be changed remotely by changing the voltage level on pin 3. A resistor that can connect pin 3 to Vs

Added to increase the threshold for A121. The impedance of pin 3 is about 10k ohms. (See Figure B)

4. PIN 5, analog display

Pin 5 provides a positive analog pulse output from the preamplifier section before the discriminator with a rise time

about 10 ns. At highest sensitivity (pin 3 = 0 volts), the amplitude of this pulse is proportional to the input charge A = 15V/pC. At threshold, this would correspond to a 120 mV pulse. The magnitude of the analog pulse if there is voltage on pin 3

Divide the resulting voltage by the same threshold decay factor. Example: If 1.3 volts is present on pin 3

(6 dB attenuation is a multiple of 2), the size of the analog pulse will be 60 mV. This output must be capacitively coupled to

External circuitry to monitor detector gain changes by performing pulse height analysis.

5. PIN 9, output

The final output stage of the A121 is produced by a 74AC00 gate with a 200 ohm series resistor.

Detector A121

1 NF

(HV)

200

VS

1

I/O 9

The PC121 is a printed circuit board designed to facilitate testing of the A121. Please visit http://www.amptek.com/

a121.html for full specs.