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from the conventional differential amplifier, in that in a conventional circuit, the same
current flows in the input and load transistors, while in the proposed circuit, the
currents in the input and load transistors are I
C1
/2 and I
C2
/2, respectively, which are
not equal; and it is by controlling these two currents by the control voltage, by the
circuit of Fig. 1, that a wide dynamic range VGA is obtained.
V
DD
M
1
M
4
M
3
I
O
V
C
I
C1
I
C2
C
1
C
2
M
2
M
5
M
6
I
O
V
SS
Fig. 1.
Circuit diagram of control stage [2]
V
C
Fig. 2.
Decibel scale plot of current ratio √ (I
C2
/I
C1
) of control circuit