Pre amplifier

The signal from PMT was amplified at a gain of $\sim$10 on a pre amplifier card. The average output from PMT per one photo-electron was 1.8 pC in charge and it corresponded to a pulse hight of $\sim$20 mV with 50$\Omega$ load with less than 5 ns pulse width.

The pre amplifier consisted of a non-inverting gain circuit using a monolithic operational amplifier (National Semiconductor CLC401) . Criteria for operational amplifier selection was the bandwidth. The CLC401 was chosen because it is a wideband fast-settling (0.1% settling in 10 ns) operational amplifier with the -3 dB bandwidth of 150 MHz and rise/fall time of 2.5 ns. Fig. 39 shows a circuit diagram of pre amplifier unit. This unit is made of CLC401, protection diodes, resistors and capacitors. The 50 $\Omega$ resistors were used for $R_{in}$ and $R_{out}$, in order to make the impedance matching to 50 $\Omega$. The circuit gain G is decided by, G = ${(R_{1}+R_{2}})/{R_{1}}$. The gain of $\times$20 was chosen with $R_{1}$ = 75 $\Omega$ and $R_{2}$ = 1.5 K $\Omega$, in order to achieve circuit gain of $\times$10 (Output 50 $\Omega$ resister and 50 $\Omega$ makes the gain of pre amplifier card $\times$10). In order to reduce the noises, two 10 $\Omega$ resistors were used at power supply line both positive and negative.

図 39: Circuit diagram of the Pre amplifier Circuit Unit made of CLC401, resistors, capacitors and protection diodes.

The pre amplifiers card were mounted on RICH vessel to minimize the cable length and avoid possible signal degradation. Each card consisted of 16 operational amplifier circuits and the card was composed of five copper layers to guard the signals from outer noises.