Datasheet

A(V/V) = K x 
R
F
R
G
x
1
1 - V
G
1 + e
V
C
LMH6502
www.ti.com SNOSA65D –OCTOBER 2003–REVISED MARCH 2013
ADJUSTING OFFSET
Offset can be broken into two parts; an input-referred term and an output-referred term. The input-referred offset
shows up as a variation in output voltage as V
G
is changed. This can be trimmed using the circuit in Figure 59 by
placing a low frequency square wave (V
LOW
= 0V, V
HIGH
= 2V into V
G
with V
IN
= 0V, the input referred V
OS
term
shows up as a small square wave riding a DC value. Adjust R
10
to null the V
OS
square wave term to zero. After
adjusting the input-referred offset, adjust R
14
(with V
IN
= 0, V
G
= 0) until V
OUT
is zero. Finally, for inverting
applications V
IN
may be applied to pin 6 and the offset adjustment to pin 3. These steps will minimize the output
offset voltage. However, since the offset term itself varies with the gain setting, the correction is not perfect and
some residual output offset will remain at in-between V
G
's. Also, this offset trim does not improve output offset
temperature coefficient.
Figure 59. Nulling the output offset voltage
GAIN ACCURACY
Defined as the actual gain compared against the theoretical gain at a certain V
G
(results expressed in dB).
Theoretical gain is given by:
(4)
Where K = 1.72 (nominal) & V
C
= 90mV @ room temperature.
For a V
G
range, the value specified in the tables represents the worst case accuracy over the entire range. The
"Typical" value would be the worst case difference between the "Typical Gain" and the "Theoretical gain". The
"Max" value would be the worst case difference between the max/min gain limit and the "Theoretical gain".
GAIN MATCHING
Defined as the limit on gain variation at a certain V
G
(expressed in dB). Specified as "Max" only (no "Typical").
For a V
G
range, the value specified represents the worst case matching over the entire range. The "Max" value
would be the worst case difference between the max/min gain limit and the typical gain.
NOISE
Figure 60 describes the LMH6502's output-referred spot noise density as a function of frequency with A
VMAX
=
10V/V. The plot includes all the noise contributing terms. However, with both inputs terminated in 50Ω, the input
noise contribution is minimal. At A
VMAX
= 10V/V, the LMH6502 has a typical input-referred spot noise density (e
in
)
of 7.7nV/ flat-band. For applications extending well into the flat-band region, the input RMS voltage noise can
be determined from the following single-pole model:
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