A 72GS/s, 8-bit DAC-based Wireline Transmitter in 4nm FinFET CMOS for 200+Gb/s Serial Links

Spectrally Efficient DMT Operation With BER-Informed Dynamic Bit and Power Loading

“…Although our experimental results are obtained using commercially available hardware as opposed to the silicon implementations in [7], [8], the specifications, such as speed and resolution, are comparable to those of the reported ADCs and DACs in today's wireline transceivers. Both the DAC and the ADC have 8 bits of vertical resolution [40], [41]-with the former having an effective number of bits (ENOB) of 5.5 bits at 30 GHz-and the measured noise in the setup is about 3.1 mV rms .…”

“…A spectral efficiency of 2.5 b/sample was also reported in [7], but at a BER of 2 × 10 −4 with a channel loss of 28 dB at 1 /4 the data rate of that work, whereas BPPA afforded a BER of 2 × 10 −5 at 33 dB loss at 1 /4 the data rate of our system. A higher spectral efficiency, namely 2.94 b/sample, was reported in [8]-although this number is based on the line rate and includes FEC overhead; the payload is 2.56 times the data converter sampling rate, not 2.94 times-but at 9 dB of channel loss at f s /2, which is 17 dB lower than the channel loss at f s /2 of our experimental demonstration, and with a pre-FEC BER of 5 × 10 −4 , an order of magnitude higher than the BER after BPPA in our work.…”

“…Both the DAC and the ADC have 8 bits of vertical resolution [40], [41]-with the former having an effective number of bits (ENOB) of 5.5 bits at 30 GHz-and the measured noise in the setup is about 3.1 mV rms . The DAC and ADC in [7] also have at least 8 bits of resolution, and so does the DAC in [8]. Finally, note that further improvement in our setup may be possible if we can independently control the IBO at the receiver using a VGA.…”

“…Existing efforts in DMT for wireline signaling can be classified into three categories: those with only bit loading, those with only power loading, and those with both bit and power loading. The DMT implementations or models in [7], [8], [10], [12] used uniform bit allocation across their subchannels (although [7] did bit-load in a very coarse way by reducing the constellation size of only 1 of 15 sub-channels), but they used power loading to improve the performance in the sub-channels facing a higher loss. By contrast, [5], [17] utilized bit loading but forwent power loading.…”

“…That work used the same fixed quadrature-amplitude modulation (QAM) in each DMT sub-channel (except for the highest-frequency one) regardless of its SNR or BER. Another work [8] reported orthogonal frequency-division multiplexing (OFDM)-which is the same as DMT in this context-operation at a line rate of 212 Gb/s (with a payload of 184 Gb/s when error correction overhead is disregarded) but a channel loss at half the sampling rate of 9 dB. In the present article, we demonstrate via simulations and measurements that a significant data rate increase with DMT is achievable over channels with higher losses through a BER-informed bit loading and power loading approach.…”