KLM signal out

The KLM subsystem consists of barrel KLM and end-cap KLM. Barrel KLM is divided into forward and backward parts and each part consists of 8 sectors. End-cap KLM also consists of forward and backward parts and each part has 4 sectors. Each sector has 15 superlayers for barrel KLM and 14 superlayers for end-cap KLM. Each superlayer consists of 2 RPC layers. The output of superlayers has 48 copper strips (barrel $\phi$, $z$, and end-cap $\theta$ readout) or 96 copper strips (end-cap $\phi$ readout). Raw output signals are sent to readout boards, located at the Belle detector, to discriminate noise signals and then the number of channels is reduced by using a time-multiplex circuit implemented on Xilinx FPGAs mounted on the readout boards. The time-multiplex circuit converts the hit strip information of each 12-strip inputs to the timing signals of one channel output using a 10 MHz system clock. The output signal also has time information of the earliest input among 12 strips (Fast-OR). Fig.  shows a schematic diagram of signals of the readout board output. A Fast-OR signal is sent first, and then the converted position information is sent next. Finally, a marker signal which shows the end of position information and a parity signal which is used for checking the number of hit strips are sent. Thus, one signal train lasts at least 1.65 $\mu$s (max. 1.75 $\mu$s). The length depends on the timing of raw signal inputs, because Fast-OR is asynchronous to the system clock. The output signals are sent to the TDC inputs in the electronics hut via 50-m long twisted pair cables. For the triggering purpose, barrel $z$ and end-cap $\theta$ readouts are used.

Figure: Schematic diagram of readout board output signals.