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8/10/2019 Current Reuse
http://slidepdf.com/reader/full/current-reuse 1/2
2. CURRENT REUSE CASCADE MPL IFIER
J n order to achieve a system with low power consumption operati11g in the
6 GHz band the power consumption of each build ing block has to be
minimized by focusing on the el imination
of
any possible power wastages .
n addition due to the high operating frequency the rniUimeter-wave CMOS
amplifier has to operate at a significant fraction
of
the cut-off frequency of the
transistor. Currently it
is
difficult to obtain sufficient gain using a conventional
single-stage amplifier. However increasing the number of stages in a cascade
connection increases the power consumption. Therefore the approach to
optimum power usage is to improve the gain ofeach single-stage block. In this
section a 60 GHz ampl ifier has been designed to demonstrate a building block
for
reduced power consumption. This amp
li
fie r implements a current-reuse
technique to
be
explained in the follow ing sections. Although there are otber
amplifiers that use an alternative current-reuse teclmique
67
-
7
for
bo
osting the
gain
of
microwave c
ir
cuits without having an accompanied increase in power
consumption the technique is difficult to apply at millimeter-wave frequencies
since many passive components are required in the circuit The passive
components usually leads to high insertion losses at high frequencies. n th is
work a current-reuse technique
fo
r gain-boosting without consuming
additional power bas beeo proposed through a simple
to
pology.
8/10/2019 Current Reuse
http://slidepdf.com/reader/full/current-reuse 2/2
2 1 Principles o Operation
Du
ri
ng operation, this amp
li
fier reuses
th
e drain current to bias two
transistors, as in the case of the cascode topology, and feeding
th
e signal
from one stage
to
the other through a resonance path. A review
of
the
conventional cascode topology, shown in Fig. I0-4 a),
re
veals that the
cascode transistor M2 does not effectively contribute to the gain.
The
common-gate cascode transistor may increase the output impedance by a
factor of g
r r
2
where
2
and r
2
is the transconductance and the dra in
sou
rc
e resis
ta
nce
of
M2, but it does not increase the ga
in
in the amplifier
because the load impedance is always
li
mited to a low value in a microwave
circuit. The gain is provided by the common-source transistor of the
topology.
As
a result, M2 is main ly used to improve the
re
verse isolation. To
improve the gain, the function of the common-gate transistor M2 should
be
re-visited. From here, a new cascade circuit shown in Fig. 10-4 b) is
proposed , where
an
inductor at the gate of a common-gate transistor is
inse11cd By using this
ga
te inductor, the operation of M2 changes from a
common-gate amplifier
to
that of a common-source. A cascade connection is
formed by the feed-through
of
the high-frequency signal through the gate
sourcc capaci t
or
of
M2, which results in gain-boosting. This circuit
is
referred
to
as a current-reuse cascade amp lifier CRCA), hereafter.
The
operation of the
CRCA
is further desc
ri
bed below.