Datasheet

LMH6624
SNOSA42F –NOVEMBER 2002–REVISED MARCH 2013 www.ti.com
Figure 51. Inverting Amplifier Configuration
TOTAL INPUT NOISE vs. SOURCE RESISTANCE
To determine maximum signal-to-noise ratios from the LMH6624/LMH6626, an understanding of the interaction
between the amplifier’s intrinsic noise sources and the noise arising from its external resistors is necessary.
Figure 52 describes the noise model for the non-inverting amplifier configuration showing all noise sources. In
addition to the intrinsic input voltage noise (e
n
) and current noise (i
n
= i
n
+
= i
n
−
) source, there is also thermal
voltage noise (e
t
= √(4KTR)) associated with each of the external resistors. Equation 1 provides the general form
for total equivalent input voltage noise density (e
ni
). Equation 2 is a simplification of Equation 1 that assumes
Figure 52. Non-Inverting Amplifier Noise Model
(2)
R
f
||R
g
= R
seq
for bias current cancellation. Figure 53 illustrates the equivalent noise model using this assumption.
Figure 54 is a plot of e
ni
against equivalent source resistance (R
seq
) with all of the contributing voltage noise
source of Equation 2. This plot gives the expected e
ni
for a given (R
seq
) which assumes R
f
||R
g
= R
seq
for bias
current cancellation. The total equivalent output voltage noise (e
no
) is e
ni
*A
V
.
Figure 53. Noise Model with R
f
||R
g
= R
seq
16 Submit Documentation Feedback Copyright © 2002–2013, Texas Instruments Incorporated
Product Folder Links: LMH6624