Biomedical Engineering Reference
In-Depth Information
Fig. 6 Simulation results of
low noise amplifier (LNA) S 11
and S 21 versus C 2 variation
Fig. 7 Schematic of the
squarer
Squarer
The schematic of the proposed squarer is shown in Fig. 7 [ 13 ]. Transistors NM 1 4
have the same sizing and the same DC biasing point in saturation region. Differential
RF input signals are fed into NM 1 2 to perform squaring function while NM 3 4 are
AC grounded, so as to cancel the output DC components. The total biasing current
is set by the current source I bias .NM 5 6 are cascode stages to enhance the squarer
output impedance. Large output impedance is desired to boost the output voltage
swing, hence active load is used here using PMOS transistors PM 1 2 and they are
biased with a common-mode feedback (CMFB) circuit. It is well known that active
load value decreases with increasing frequency due to the large parasitic capacitance.
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