Biomedical Engineering Reference
In-Depth Information
Fig. 13 Low-noise amplifier
(LNA) circuit schematic
together with the added
inductors
Vdd
L L
R L
L D
M3
V Cascode
M2
I buffer
L C
R S
L 1
C 1
L g
M1
C P
V in
L 2
C 2
L S
Design Example for Ultra-Wideband Receiver
The general block diagram of a UWB receiver was introduced previously in Fig. 7 .
In this section, an example design and implementation of a UWB LNA and a mixer
as two of the most important blocks of the receiver will be presented.
Ultra-Wideband Low-Noise Amplifier
Gain and Bandwidth
In the design presented, a CS (Common Source) configuration with inductive de-
generation and a multi-section reactive network for input matching is utilized. The
matching network is first proposed in [ 24 ]. Also, two auxiliary inductors are added
to boost the bandwidth of the amplifier. In the circuit shown in Fig. 13 , the drain
current i d can be written as
i d =
V G g m
s ( C p +
F ( s ) V in g m
s ( C p +
C gs ) ω t L s =
C gs ) ω t L s ,
(1)
assuming F ( s ) is the Chebyshev filter transfer function. In the above analysis, C gd
is not taken into account. This is mainly because of the very low impedance of the
cascode stage seen from drain of M 1 . This will result in very weak Miller effect on
gate of M 1 ,so C M is
C M =
C gd ( 1
+
g m ( r o
R L ) ) .
(2)
Here, R L =
1/ g m2 is small enough to make the Miller capacitance negligible, so the
LNA gain without considering L D and L C will be
v out
v in =
F ( s ) g m
s ( C p +
( sL L + R L )
C gs ) ω t L s
C gd3 ) .
(3)
1
+
sR L ( C db2 +
C gd3 )
+
s 2 L L ( C db2 +
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