clc522 National Semiconductor Corporation, clc522 Datasheet - Page 8

• Manufacturer Part Number: clc522
• Description: Wideband Variable-gain Amplifier
• Manufacturer: National Semiconductor Corporation

www.national.com
Typical Performance Characteristics
−1dB Compression at Maximum Gain
Application Division
Theory of Operation
The CLC522 is a linear wideband variable gain amplifier as
illustrated in Figure 1 . A voltage input signal may be applied
differentially between the two inputs (+V
single-endedly by grounding one of the unused inputs.
The CLC522 input buffers convert the input voltage to a
current (I
(V
resistor (R
stage with a current gain of 1.85. The voltage controlled
two-quadrant multiplier attenuates this current which is then
converted to a voltage via the output amplifier. This output
amplifier is a current-feedback op amp configured as a tran-
simpedance amplifier. Its transimpedance gain is the feed-
back resistor (R
are all voltages. The output voltage can easily be calculated
as seen in Eq. 1.
INPUT
= +V
Rg
g
) that is a function of the differential input voltage
). This current (I
IN
− −V
f
). The input signal, output, and gain control
IN
) and the value of the gain-setting
FIGURE 1.
Rg
) is then mirrored to a gain
DS012718-25
IN
, -V
DS012718-26
IN
), or
(1)
(Continued)
8
The gain of the CLC522 is therefore a function of three
external variables; R
gain control voltage (V) has an ideal input range of −1V
+ 1V. At V
as expressed in Eq. 3.
Notice also that Eq. 3 holds for both differential and single-
ended operation.
Choosing R
R
peak
input voltage (V
the maximum allowable current through R
1.8mA. Once A
and desired output voltages, R
5. These values of R
the minimum possible values that meet the input voltage and
maximum gain constraints. Scaling the resistor values will
decrease bandwidth and improve stability.
g
is calculated from Equation 4. V
g
= + 1V, the gain of the CLC522 is at its maximum
f
and R
Vmax
pk
) determined by the application. I
g
g
is determined from the minimum input
f
, R
and R
f
and V
g
are
f
g
is then determined using Eq.
as expressed in Eq. 2. The
input max
g
is the maximum
and is typically
Rgmax
(2)
(3)
(4)
(5)
V
is
g