The scientific goals of the KamLAND experiment presents several challenging experimental problems with implications for electronic system design. Reconstruction of signal events and efficient rejection of backgrounds both depend on the quality of the primary data. In an experiment such as KamLAND, where the number of expected true events is not large and the potential backgrounds are numerous, it is clear that all information that can contribute to the quality of the data should be recorded. The KamLAND experiment will use high-speed (~400 MHz) waveform recording of the photomultiplier tube (PMT) outputs to capture as much of this essential signal information as possible.

The KamLAND front end electronic (FEE) system is based on an innovative Application Specific Integrated Circuit (ASIC) developed at LBNL, the Analog Transient Waveform Digitizer (ATWD). The ATWD simultaneously can capture four channels of independent signals at sample speeds from 200 MHz to well over one GHz. The sampling action is generated internally without the need for high-speed external clocks. The use of the ATWD permits extremely high sampling speeds while allowing the engineer to design for a conservative board-level clock frequencies (e.g. 40 MHz). The ATWD is equipped with a common-ramp parallel Wilkinson 10-bit ADC, permitting the direct conversion on-chip of the captured analog signal. Digitization and readout of the entire 128-sample waveform requires about 25 microseconds at 40 MHz for the 10-bit range.

The FEE design includes 12 electronics channels per board. A total of 200 boards will be used to instrument all KamLAND PMT's, including both the the inner and outer detectors. The board circuitry for each channel includes two ATWD chips, which alternately acquire waveforms in a ping-pong arrangement. This setup almost completely eliminates deadtime from the electronics, as the second ATWD can acquire data if a pulse arrives which the first ATWD is digitizing. The multiple input channels to each ATWD are used to acquire the same waveforms at different gains. This gives the FEE boards a very large dynamic range, as the same waveform can be analyzed at a lower gain if it overflows the highest-gain channel. With this setup, we can accurately record waveforms which vary in size by over three orders of magnitude.

The basic design of the FEE board has been extensively tested with four prototype boards. These boards have validated the main features of the

KamLAND FEE design, including the dual-ATWD ping-pong scheme and the use of multiple ATWD channels to extend the dynamic range. We used these boards to study the noise environment at the KamLAND experimental site in an on-site test in October 2000, as described in a separate Annual Report. Figure 1 shows a sample multiple-pulse waveform collected during these tests. This sample data illustrates the ability of this electronics setup to resolve multiple pulses in close time sequence. Our experience with the prototype boards also suggested some improvements to the board design, most notably the introduction of separate power distribution for the analog and digital components of the board to prevent crosstalk signals from the digital components from appearing in the recorded analog waveforms.

We now have the final design of the FEE boards in hand, and we are beginning to move into full-scale production. We have developed a testing routine for ATWD chips, as described in a separate Annual Report. We expect to begin full scale board production in April, and plan to test a full crate of electronics at the KamLAND site by early summer.

Figure 1. A sample multiple-pulse waveform recorded with the prototype FEE board in the on-site KamLAND electronics test. Both raw and pedestal-subtracted waveforms are shown, with the pedestal in dashed red, and a flat baseline in dashed green. (The horizontal scale is about 2.3 ns per sample, while the vertical is approximately 0.8 mV per count.)