/bɜːrt/
n. "Test instrument measuring bit error ratios in high-speed serial links using known PRBS patterns."
BERT, short for Bit Error Rate Tester, comprises pattern generator and error detector validating digital communication systems by transmitting known sequences through DUT (Device Under Test) and comparing received bits against expected, quantifying performance as BER = errors/total_bits (target 1e-12 for SerDes). Essential for characterizing CTLE, DFE, and CDR under stressed PRBS-31 patterns with added sinusoidal jitter/SJ.
Key characteristics of BERT include: Pattern Generator produces PRBS7/15/23/31 via LFSR or user-defined CDR-lock patterns; Error Counter accumulates bit mismatches over test time (hours for 1e-15 BER); Jitter Injection adds TJ/SJ/RJ stressing receiver tolerance; Loopback Mode single-unit testing via DUT TX→RX shorting; Bathtub Analysis sweeps voltage/jitter revealing BER contours.
Conceptual example of BERT usage:
# BERT automation script (Keysight M8040A API example)
import pyvisa
rm = pyvisa.ResourceManager()
bert = rm.open_resource('TCPIP::BERT_IP::inst0::INSTR')
# Configure PRBS-31 + 0.5UI SJ @ 20% depth
bert.write(':PAT:TYPE PRBS31')
bert.write(':JITT:TYPE SINU; FREQ 2e9; AMPL 0.1') # 2GHz SJ, 0.1UI
# Run 1e12 bit test targeting 1e-12 BER
bert.write(':TEST:START')
bert.write(':TEST:BITS 1e12')
bert.query(':TEST:BER?') # Returns '1.23e-13'
# Bathtub sweep: Vth vs RJ
bert.write(':SWEEp:VTH 0.4,0.8,16') # 16 voltage steps
bert.write(':SWEEp:RUN')
bathtub_data = bert.query(':TRACe:DATA?') # BER contoursConceptually, BERT functions as truth arbiter for USB4/DisplayPort PHYs—injects PRBS through stressed channel, counts symbol errors post-CTLE/DFE while plotting Q-factor bathtub curves. Keysight M8040A/MSO70000 validates 224G Ethernet hitting 1e-6 BER pre-FEC, correlating eye height to LFSR error floors; single-unit loopback mode transforms FPGA SerDes into self-tester, indispensable for PCIe5 compliance unlike protocol analyzers measuring logical errors.