5.3.1 Standard Pulser Setup

In sections 5.3.2, 5.3.3, and 5.3.4, tests are described where signals produced by tail pulse generators (pulsers) are sent to the test pulse preamplifier inputs. The standard configuration for the pulsers is the described in the following. One pulser sends inverted signals to the Anode and Backanti preamplifiers, and the trigger output of this pulser is connected to the trigger input of a second pulser. When triggered by the first pulser, the second pulser sends non-inverted signals to the Sideanti, Wedge, Strip, and Zee preamplifiers. This configuration allows for signals of different amplitudes and polarities to be sent nearly simultaneously to the Anode and Backanti preamplifiers and the Sideanti, Wedge, Strip, and Zee preamplifiers. Throughout the testing described in the following three sections, the pulser was set to produce signals with 1 microsecond rise times and 500 microsecond decay times at a rate of 100 Hz.

5.3.2 Calibration of Electronics Channels Using the Pulser

Purpose

To measure the gain and the "offset" of the preamplifier/shaping amplifier combination for each electronics channel.

Testing Setup and Procedure

In conducting this test, initially one pulser is connected to the Anode preamplifier test pulse input while the other preamplifier test pulse inputs are disconnected. For each of ten pulser amplitude settings, the amplitude of the input signal to the preamplifier is measured on the scope and data is acquired until 1000 events have been collected. The procedure is similar for the other electronics channels. However, since data acquisition is only triggered when a Slow Anode signal triggers the SCA, it is necessary to pulse on the Anode electronics channel in addition to the channel being tested. Thus, in testing the Backanti, Sideanti, Wedge, Strip, and Zee electronics channels, one pulser is set to the lowest level which will still trigger the SCA. This pulser is connected to the input of the Anode preamplifier and its trigger output is connected to the second pulser. The second pulser is then connected to the channel being tested. As described for the Anode, scope measurements are made and data is acquired as the second pulser is ramped through ten amplitudes. Throughout the testing, the gain of the Fast Anode shaping amplifier is set to 38 and the gains of the other amplifiers are set to 5. During data acquisition, the high voltage is off.

Analysis and Results

Figures 5.3-1a to 5.3-1h show how the amplitude of the signal at the input to the ADC varies over the ten pulser settings for each electronics channel. For each IPC, eight graphs are plotted: one for each of the seven electronics channels and one showing the fastslow ratio at each setting. The fast amplifier (the unipolar shaping amplifier with a 200 ns time constant) saturates at a lower level than the other shaping amplifiers so fewer points are observed on the "FAST" and "FASTSLOW" graphs. For each point, the horizontal coordinate ("input to preamp") comes from a scope measurement of the signal at the input to the preamplifier of the electronics channel being tested, and the vertical coordinate ("input to ADC") is the mean of the digitized signal amplitudes converted to a voltage. Each mean value is found by calculating a Gaussian fit to a pulse height histogram. The conversion to voltage is based on the fact that a 10 Volt signal has the minimum amplitude which will saturate the 12 bit ADC.

A linear least squares fit is calculated to the data for each electronics channel giving a slope and an offset. The fits are shown in the figures. The slopes correspond to the gains of the preamplifier/shaping amplifier combinations for each electronics channel. The offsets correspond to the extrapolated signal amplitudes at the ADC inputs when the amplitude of the signal at the input to the preamp is zero. The fastslow ratio is calculated according to the following algorithm: The Fast Anode offset is subtracted from the Fast Anode input to ADC for each point and each result is divided by the gain of the Fast Anode channel. A similar procedure is carried out for the Slow Anode for each point. The fastslow ratio results when each of the Fast Anode results are divided by the corresponding Slow Anode results for each point. In Table 12, the gains and offsets are given for each electronics channel for the four IPCs.

5.3.3 Temperature Sensitivity of Analog Electronics

Purpose

To measure the gain and the offset of the preamplifier/shaping amplifier combination for each electronics channel and the noise in each electronics channel at three different temperatures in order to look for temperature variations in these parameters.

Table 12: Gains and Offsets for the Electronics Channels

Testing Setup and Procedure

During this test, the IPC is placed on a hot plate and enclosed in an insulating shell. Three temperature monitors are used: two thermocouple probes are connected to opposite sides of the IPC body and a temperature transducer is housed within the E-box. In contrast to the previous tests where the electronics channels are tested separately, all six preamplifiers are simultaneously connected to a pulser as described in section 5.3.1. At temperatures of 60°C, 45°C, and 25°C for LE1, LE2, and HE1 and 45°C and 25°C for HE2, one thousand events are collected at each of ten different pulser settings. Throughout the testing, the gain of the Fast Anode shaping amplifier is 38, the gains of the Slow Anode and Backanti shaping amplifiers are 5, and the gains of the Sideanti, Wedge, Strip, and Zee shaping amplifiers are 20. The high voltage is turned on and set to typical operating voltages during data acquisition.

Analysis and Results

Figures 5.3-2a to 5.3-2h show how the ampltude of the signal at the input to the ADC varies over the ten pulser settings for each electronics channel for each temperature. Eight graphs are plotted for each IPC: one for each of the seven electronics channels and one showing the the fastslow ratio for each setting. The fast amplifier saturates at a lower level than the other shaping amplifiers so fewer points are observed on the "FAST" and "FASTSLOW" graphs. For each point, the horizontal coordinate ("pulser level setting") is the setting of the knob which controls the pulser amplitude, and the vertical coordinate ("input to ADC") is the mean of the digitized signal amplitudes converted to a voltage. Each mean value is found by calculating a Guassian fit to a pulse height histogram.

A linear least squares fit is calculated for the data for each electronics channel giving a slope (the "gain") and an offset. The fits for the data taken at 25°C are shown in the figures. The algorithm used to calculate the fastslow ratio is given in section 5.3.2. Figures 5.3-3a to 5.3-3h show the temperature dependence of the fit parameters for the seven electronics channels for the four IPCs.

Figures 5.3-4a to 5.3-4h show how the electronic channel noise varies over the ten pulser settings for each electronics channel and for each temperature. For each pulser setting, the noise in a given channel is measured by the FWHM of the Gaussian fit to a pulse height histogram. Figures 5.3-5a to 5.3-5d show the temperature dependence of the noise level for the seven eletronis channels.

Concerning the data presented in this section, the following items are noted:

1. The HE1 Wedge, Strip, Sideanti, and Fast Anode are the only electronics channels which show significant variation in their fit parameters with temperature.

2. There is a deviation from linearity for the LE2 Fast Anode channel at 45°C due to a change in the pulser rise time. This problem was corrected for all subsequent data acquisition.

3. For LE1, the Fastslow ratio is temperature dependent for low amplitude signals.

4. The majority of electronics channels show a tendency for noise levels to increase slightly with increasing temperature.

5.3.4 Crosstalk Measurements

Purpose

To measure the interference between electronics channels.

Testing Setup and Procedure

Crosstalk measurements are made by connecting a pulser to one of the six preamplifiers and measuring the amplitudes of the signals at the shaping amplifier outputs of the other five. In performing this test, the pulser amplitude is adjusted so that the amplitude of the signal at the output of the pulsed channel's shaping amplifier is 4.0 V. The scope is used to measure all six signal amplitudes. For each IPC, two sets of crosstalk measurements are made: one set of measurements is made before the E-box is mounted to the IPC body to measure the crosstalk in the E-box, while the second set of measurements is made once the IPC is fully assembled.While measuring the crosstalk, the fast shaping amplifier gain is set to 38 (except for the measurements made for HE1 with the E-box disconnected from the IPC where the fast shaping amplifier gain was set to 15). In all cases, the gains of the other amplifiers are set to 5 and the high voltage is off.

Analysis and Results

Tables 13 and 14 contain the crosstalk measurements for the four IPCs. The crosstalk measurements made with the E-box disconnected from the IPC are given in Table 13, while those made with the E-box connected to the IPC are given in Table 14. In both tables, the measurements are quoted as a percentage of 4.0 V. A negative entry indicates that the crosstalk signal is inverted relative to the polarity of a signal for an x-ray event.

Concerning the crosstalk measurements, the following observations are made:

1. With the E-box connected to the IPC, the magnitudes of the largest crosstalk signals on the Backanti are 0.9%, 0.8%, 1.0%, and 0.2% for LE1, LE2, HE1, and HE2 respectively.

2. With the E-box connected to the IPC, the magnitudes of the largest crosstalk signals on the Sideanti are 2.6%, 2.3%, 2.8%, and 0.5% for LE1, LE2, HE1, and HE2 respectively.

3. The mutual crosstalk between the Wedge, Strip, and Zee channels is larger with the E-box connected to the IPC than it is with the E-box disconnected from the IPC due to the relatively large capacitances between the electrodes in the Wedge, Strip, and Zee pattern.

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