Design and Analysis of an Electrical Balance Duplexer With Independent and Concurrent Dual-Band TX-RX Isolation

An electrical balance duplexer (EBD) supports dual-band TX-RX isolation enabling frequency-division duplexing (FDD) operation at 5-7 GHz for Wi-Fi 6/6E. A programmable balance network in the EBD can balance the antenna impedance (
$Z_{\text {ANT}}$
) in the TX channel and RX channel independently and simultaneously. An on-chip passive bandstop filter as a part of the balance network is implemented, achieving sub-2-dB passband insertion loss (IL) and >20-dB stopband rejection with 10% frequency spacing. This filter separates two impedance tuners in the balance network and enables the independent tunability at two bands. A comprehensive and rigorous analysis of general
LCR
two-ports shows the limit of the
$s_{21}$
frequency selectivity when built with finite-
$Q$
elements. The analysis guides the filter design, which guarantees the maximum frequency selectivity. The analysis is then extended to
LCR

${N}$
-ports as the complete analysis. The EBD provides >40-dB isolation in an 80-MHz channel bandwidth in the TX band (5-6 GHz), for any
$Z_{\text {ANT}}(f_{\text {TX}})$
within VSWR = 2, and independently in the RX band (6-7 GHz) when
$Q_{\text {ANT}}< 4.3$
. The EBD is designed for ≤4-dB RX IL and ≤3.8-dB TX IL, and it supports +29-dBm TX output. The EBD is implemented in Towerjazz 65-nm RF silicon-on-insulator (SOI) CMOS technology and occupies an area of 2.3 mm
²
.