TLE2662 Datasheet, PDF (26/40 Pages) Texas Instruments – DUAL uPOWER JFET-INPUT OPERATIONAL AMPLIFIER WITH SWITCHED-CAPACITOR VOLTAGE CONVERTER

TLE2662
DUAL µPOWER JFET-INPUT OPERATIONAL AMPLIFIER
WITH SWITCHED-CAPACITOR VOLTAGE CONVERTER
SLOS118B – DECEMBER 1992 – REVISED AUGUST 1994
APPLICATION INFORMATION
typical application (continued)
5V
Signal ^RI
From
Preamplifier
Shutdown
SCIN
SCOUT
Voltage
Converter
FB/SD
SCREF
RF
Signal
RI
–
From
+
Amplifier 1
Transducer
RL
RF
–
To ADC
+
Amplifier 2
Figure 50. Equivalent Schematic: Amplifier 1 Driving Resistive Load,
Amplifier 2 Interfacing to an ADC
Though simple, this configuration has the inherent disadvantage of having ripple and switching-noise
components on SCOUT. These are coupled into the amplifier’s signal path, effectively introducing distortion into
the output waveform. The effect is most pronounced when the outputs are driven low, loading the negative rail
generated by the charge pump. A first approach to minimizing these effects is to increase the size of COUT using
a low-ESR type capacitor (refer to the switched-capacitor selection section under capacitor selection and output
ripple). Figures 51 and 52 compare the ripple and noise present at the amplifier output with COUT = 10 µF and
COUT = 100 µF, respectively, with the outputs driven low into a 600-Ω load.
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