clc522 National Semiconductor Corporation, clc522 Datasheet - Page 9

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

Application Division
Figure 2 illustrates the resulting CLC522 bandwidths as a
function of the maximum and minimum input voltages when
V
Adjusting Offsets
Treating the offsets introduced by the input and output
stages of the CLC522 is easily accomplished with a two step
process. The offset voltage of the output stage is treated by
first applying −1.1Volts on V
input stage and multiplier core from the output stage.
As illustrated in Figure 3 , the trip pot located at R14 on the
CLC522 Evaluation Board should then be adjusted in order
to null the offset voltage seen at the CLC522’s output (pin
10). Once this is accomplished, the offset errors introduced
by the input stage and multiplier core can then be treated.
The second step requires the absence of an input signal and
matched source impedances on the two input pins in order to
cancel the bias current errors. This done then +1.1Volts
should be applied to V
adjusted in order to mull the offset voltage seen at the
CLC522’s output. If a more limited gain range is anticipated,
the above adjustments should be made at these operating
points.
Gain Errors
The CLC522’s gain equation as theoretically expressed in
Eq. 2 must include the device’s error terms in order to yield
out
is held constant at 1V
FIGURE 2. Bandwidth vs. V
FIGURE 3.
g
and the trip pot located at R10
pp
g
.
, which effectively isolates the
(Continued)
inputmax
DS012718-32
vs. A
vmax
DS012718-33
9
the actual gain equation. Each of the gain error terms are
specified in the Electrical Characteristics table and are de-
fined below and illustrated in Figure 4 .
GACCU : error of A
GCNL : deviation from theoretical expressed as
.
V
V
Combining these error terms with Eq. 2 gives the gain
envelope equation and is expressed in Eq. 7. From the
Electrical Characteristics table, the nominal endpoint values
of V
Signal-Channel Nonlinearity
Signal-channel nonlinearity, SGNL, also known as integral
endpoint linearity, measures the non-linearity of an amplifi-
er’s voltage transfer function. The CLC522’s SGNL, as it is
specified in the Electrical Characteristics table, is measured
while the gain is set at its maximum (i.e. V
Typical Performance Characteristics plot lableled SGNL &
Gain vs V
through its full range. As can be seen in this plot, when the
gain
the lowest gains.
Noise
Figure 5 describes the CLC522’s input-referred spot noise
density as a function of A
contributing terms. At A
typical input referred spot noise density (e
The input RMS voltage noise can be determined from the
following single-pole model:
<
V
g high
g low
0.02%(−74cB) at V
g high
g
: voltage on V
: voltage on V
are: V
, V
as
g
g low
reduced
g high
illustrates the CLC522’s SGNL as V
: error of V
= 990mV and V
g
Vmax
g
producing A
g
producing A
from
=0 and then degrades somewhat at
FIGURE 4.
, expressed as
V max
V max
g high
. The plot includes all the noise
A
, V
= 10V/V, the CLC522 has a
V max
g low
g low
Vmin
Vmax
,
expressed as
= −975mV.
SGNL
= 0V/V.
.
±
dB.
ni
) of 5.8nV/
g
=+1.1V). The
improves
www.national.com
±
g
±
DS012718-34
is swept
mV.
(6)
to
.