Datasheet

+15V
Digital
Output
-15V
V
OCM
V
COM
V
IN+
V
IN-
V
IN-
V
IN+
OPA1632
SBOS286B –DECEMBER 2003–REVISED JANUARY 2010 www.ti.com
It is important to maintain accurate resistor matching SHUTDOWN FUNCTION
on R
1
/R
2
and R
3
/R
4
to achieve good differential signal
The shutdown (enable) function of the OPA1632 is
balance. Use 1% resistors for highest performance.
referenced to the negative supply of the operational
When connected for single-ended inputs (inverting
amplifier. A valid logic low (< 0.8V above negative
input grounded, as shown in Figure 11), the source
supply) applied to the enable pin (pin 7) disables the
impedance must be low. Differential input sources
amplifier output. Voltages applied to pin 7 that are
must have well-balanced or low source impedance.
greater than 2V above the negative supply place the
Capacitors C
1
, C
2
, and C
3
should be chosen carefully amplifier output in an active state, and the device is
for good distortion performance. Polystyrene, enabled. If pin 7 is left disconnected, an internal
polypropylene, NPO ceramic, and mica types are pull-up resistor enables the device. Turn-on and
generally excellent. Polyester and high-K ceramic turn-off times are approximately 2ms each.
types such as Z5U can create distortion.
Quiescent current is reduced to approximately
0.85mA when the amplifier is disabled. When
FULLY-DIFFERENTIAL AMPLIFIERS
disabled, the output stage is not in a high-impedance
state. Thus, the shutdown function cannot be used to
Differential signal processing offers a number of
create a multiplexed switching function in series with
performance advantages in high-speed analog signal
multiple amplifiers.
processing systems, including immunity to external
common-mode noise, suppression of even-order
nonlinearities, and increased dynamic range. OUTPUT COMMON-MODE VOLTAGE
Fully-differential amplifiers not only serve as the
The output common-mode voltage pin sets the dc
primary means of providing gain to a differential
output voltage of the OPA1632. A voltage applied to
signal chain, but also provide a monolithic solution for
the V
OCM
pin from a low-impedance source can be
converting single-ended signals into differential
used to directly set the output common-mode voltage.
signals allowing for easy, high-performance
For a V
OCM
voltage at mid-supply, make no
processing.
connection to the V
OCM
pin.
A standard configuration for the device is shown in
Depending on the intended application, a decoupling
Figure 12. The functionality of a fully differential
capacitor is recommended on the V
OCM
node to filter
amplifier can be imagined as two inverting amplifiers
any high-frequency noise that could couple into the
that share a common noninverting terminal (though
signal path through the V
OCM
circuitry. A 0.1mF or 1mF
the voltage is not necessarily fixed). For more
capacitor is generally adequate.
information on the basic theory of operation for fully
differential amplifiers, refer to the Texas Instruments
Output common-mode voltage causes additional
application note SLOA054, Fully Differential
current to flow in the feedback resistor network. Since
Amplifiers, available for download from the TI web
this current is supplied by the output stage of the
site (www.ti.com).
amplifier, this creates additional power dissipation.
For commonly-used feedback resistance values, this
current is easily supplied by the amplifier. The
additional internal power dissipation created by this
current may be significant in some applications and
may dictate use of the MSOP PowerPAD package to
effectively control self-heating.
Figure 12. Typical ADC Circuit
8 Copyright © 2003–2010, Texas Instruments Incorporated
Product Folder Link(s): OPA1632