A stepped-up tree encoder for the 10-ps Wave Union TDC

We proposed a stepped-up tree encoder (SUTE) to deal with the issue of non-thermometer-to-binary (NTH2B) for our 10-ps Wave Union FPGA TDC. The encoder is made up of two pipelining stages: a pre-encoding and a parallel-encoding, and is capable of bubble error correction (BEC) as well. With this encoding algorithm applied in Xilinx Virtex-4 FPGA, we achieved a NTH2B conversion rate of up to 100 MHz for more than 200-bit non-thermometer codes.