Frey also presented a highly
modular technique for implementing such filters from
a simple building block comprising a bipolar current mirror
whose emitters are driven by complementary emitter followers.
Log-domain filter operations are based on instantaneous
companding [4]–[7] and these previous circuits are
of theoretical and technological interest because they potentially
offer high-frequency operation, tunability, and
extended dynamic range under low power supply voltages
[8]–[14]. Log-domain circuits based on CMOS technology
were introduced [15] which need to bias in weak inversion
region. Complexity and low-bandwidth are the drawback
of this circuit.