VARIABLE GAIN AMPLIFIER HAVING WIDE GAIN VARIATION AND WIDE BANDWIDTH
There is provided a variable gain amplifier that is implemented with a CMOS device and has wide band variation and wide bandwidth by a predetermined exponential function. A variable gain amplifier having wide gain variation and wide bandwidth according to an aspect of the invention may include: a differential amplification section differentially amplifying an input signal according to a gain adjustment signal; and a gain adjustment section supplying the gain adjustment signal on the basis of an approximated exponential function determined according to a predetermined bias current, and adjusting a gain of the differential amplification section.
1 . A variable gain amplifier having wide gain variation and wide bandwidth, the variable gain amplifier comprising:
a differential amplification section differentially amplifying an input signal according to a gain adjustment signal; and
a gain adjustment section supplying the gain adjustment signal on the basis of an approximated exponential function determined according to a predetermined bias current, and adjusting a gain of the differential amplification section.
2 . The variable gain amplifier of claim 1 , wherein the approximated exponential function satisfies the following equation:
f
(
x
)
=
[
1
+
ax
+
k
(
ax
)
2
/
2
]
[
1
-
ax
+
k
(
ax
)
2
/
2
]
,
Equation
where k and a are constants determined by the bias current, and x is an independent variable.
3 . The variable gain amplifier of claim 1 , wherein the gain adjustment section comprises a current converter converting a current level of a predetermined adjustment signal into a current level of the gain adjustment signal having a different current level from that of the adjustment signal.
4 . The variable gain amplifier of claim 3 , wherein the gain adjustment section further comprises:
a voltage-to-current converter converting a voltage level of a control signal from the outside into the current level of the adjustment signal; and
a bias circuit supplying the bias current to the voltage-to-current converter.
5 . The variable gain amplifier of claim 3 , wherein the current converter comprises:
a plurality of amplification units connected in parallel with each other and each having at least two amplifier devices connected in series to each other between a driving power supply terminal supplying predetermined driving power and a ground terminal; and
a current squaring unit connected in parallel with the amplification units between the driving power supply terminal and the ground terminal, and having a plurality of amplifier devices mirroring a current from the amplification units.
6 . The variable gain amplifier of claim 4 , wherein the voltage-to-current converter comprises:
a level converting circuit having a plurality of amplifier devices connected in parallel with each other between a driving power supply terminal supplying predetermined driving power and a ground terminal, and converting a voltage level of the adjustment signal into a current level; and
a current mirror circuit having a plurality of amplifier devices connected in parallel with each other between the level converting circuit and the ground terminal, and mirroring a current from the level converting circuit.
7 . The variable gain amplifier of claim 4 , wherein the bias circuit comprises:
a bias unit mirroring a current from the predetermined driving power and supplying the bias current; and
a cascode amplification unit amplifying the bias current.
8 . The variable gain amplifier of claim 1 , wherein the differential amplification section further includes:
a cascode input terminal increasing an operating frequency bandwidth by adjusting the capacitance of an input terminal of the input signal; and
an inductive active load connected to an output terminal of the differential amplification section, adjusting the capacitance of the output terminal, and increasing an operating frequency bandwidth.