Application Division (Continued)
Figure 2
illustrates the resulting CLC522 bandwidths as a
function of the maximum and minimum input voltages when
V
out
is held constant at 1V
pp
.
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
g
, which effectively isolates the
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
g
and the trip pot located at R10
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
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
Vmax
, expressed as ±dB.
GCNL : deviation from theoretical expressed as ±
.
V
g
high : voltage on V
g
producing A
Vmax
.
V
g
low : voltage on V
g
producing A
Vmin
= 0V/V.
∆V
g
high,∆V
g
low : error of V
g
high,V
g
low expressed as ±mV.
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
g
are: V
g
high = 990mV and V
g
low = −975mV.
(6)
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
g
=+1.1V). The
Typical Performance Characteristics plot lableled ″SGNL &
Gain vs V
g
″illustrates the CLC522’s SGNL as V
g
is swept
through its full range. As can be seen in this plot, when the
gain as reduced from A
V
max, SGNL improves to
<0.02%(−74cB) at V
g
=0 and then degrades somewhat at
the lowest gains.
Noise
Figure 5
describes the CLC522’s input-referred spot noise
density as a function of A
V
max. The plot includes all the noise
contributing terms. At A
V
max = 10V/V, the CLC522 has a
typical input referred spot noise density (e
ni
) of 5.8nV/ .
The input RMS voltage noise can be determined from the
following single-pole model:
DS012718-32
FIGURE 2. Bandwidth vs. V
inputmax
vs. A
vmax
DS012718-33
FIGURE 3.
DS012718-34
FIGURE 4.
CLC522
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