Datasheet

FREQUENCY (Hz)
GAIN (dB)
1k 10k 100k 1M 10M 100M
Gain LMP7701
Phase LMP7701
PHASE (°)
100
80
60
40
20
0
-20
80
100
120
140
160
180
200
SENSOR
V
+
V
-
R
S
+
-
I
B
V
IN
+
V
S
+
-
R
1
R
2
LMP7707, LMP7708, LMP7709
www.ti.com SNOSAW5B –JUNE 2007–REVISED MARCH 2013
Figure 49. Noise Due to I
BIAS
USAGE OF DECOMPENSATED AMPLIFIERS
This section discusses the differences between compensated and decompensated op amps and presents the
advantages of decompensated amplifiers. In high gain applications decompensated amplifiers can be used
without any changes compared to standard amplifiers. However, for low gain applications special frequency
compensation measures have to be taken to ensure stability.
Feedback circuit theory is discussed in detail, in particular as it applies to decompensated amplifiers. Bode plots
are presented for a graphical explanation of stability analysis. Two solutions are given for creating a feedback
network for decompensated amplifiers when relatively low gains are required: A simple resistive feedback
network and a more advanced frequency dependent feedback network with improved noise performance. Finally,
a design example is presented resulting in a practical application. The results are compared to fully compensated
amplifiers (Texas Instruments LMP7701/LMP7702/LMP7704).
COMPENSATED AMPLIFIERS
A (fully) compensated op amp is designed to operate with good stability down to gains of ±1. For this reason, the
compensated op amp is also called a unity gain stable op amp.
Figure 50 shows the Open Loop Response of a compensated amplifier.
Figure 50. Open Loop Frequency Response Compensated Amplifier (LMP7701)
This amplifier is unity gain stable, because the phase shift is still < 180°, when the gain crosses 0 dB (unity gain).
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