Datasheet

MAXIMUM GAIN =
1 +
R
2
R
1
·
R
F
R
G
K
·
2
V
IN
R
2
V
O
V
G
R
G
R
C
R
1
25:
+
-
LMH6624
LMH6505
3
1
6
7
4
R
F
GAIN (dB)
V
G
(V)
PARAMETER:
GAIN ACCURACY (TYPICAL) = B-C
GAIN ACCURACY (+MAX) = D-C
GAIN ACCURACY (-MAX) = A-C
GAIN MATCHING (+MAX) = D-B
GAIN MATCHING (-MAX) = A-B
THEORETICAL GAIN
MAX GAIN LIMIT
MIN GAIN LIMIT
TYPICAL GAIN
D
C
B
A
LMH6505
www.ti.com SNOSAT4E –DECEMBER 2005–REVISED APRIL 2013
Figure 42. LMH6505 Gain Accuracy & Gain Matching Defined
GAIN PARTITIONING
If high levels of gain are needed, gain partitioning should be considered:
Figure 43. Gain Partitioning
The maximum gain range for this circuit is given by the following equation:
(4)
The LMH6624 is a low noise wideband voltage feedback amplifier. Setting R
2
at 909Ω and R
1
at 100Ω produces
a gain of 20 dB. Setting R
F
at 1000Ω as recommended and R
G
at 50Ω, produces a gain of about 26 dB in the
LMH6505. The total gain of this circuit is therefore approximately 46 dB. It is important to understand that when
partitioning to obtain high levels of gain, very small signal levels will drive the amplifiers to full scale output. For
example, with 46 dB of gain, a 20 mV signal at the input will drive the output of the LMH6624 to 200 mV and the
output of the LMH6505 to 4V. Accordingly, the designer must carefully consider the contributions of each stage
to the overall characteristics. Through gain partitioning the designer is provided with an opportunity to optimize
the frequency response, noise, distortion, settling time, and loading effects of each amplifier to achieve improved
overall performance.
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