OP292_15 Datasheet, PDF (14/20 Pages) Analog Devices – Dual/Quad Single-Supply Operational Amplifiers

OP292/OP492
TYPICAL APPLICATIONS
DIRECT ACCESS ARRANGEMENT FOR TELEPHONE
LINE INTERFACE
Figure 36 shows a 5 V single-supply transmit/receive telephone line
interface for a modem circuit. It allows full duplex transmission
of modem signals on a transformer-coupled 600 V line in a
differential manner. The transmit section gain can be set for the
specific modem device output. Similarly, the receive amplifier
gain can be appropriately selected based on the modem device
input requirements. The circuit operates on a single 5 V supply.
The standard value resistors allow the use of a SIP-packaged
resistor array; coupled with a quad op amp in a single package,
this offers a compact, low part count solution.
TO
TELEPHONE
LINE
1:1
T1
300kΩ
300kΩ
TX GAIN ADJUST
50kΩ
1/4
OP492
20kΩ
20kΩ
20kΩ ^0.1µF
TRANSMIT
TXA
6.2V
6.2V
1/4
OP492
5V DC
5kΩ
MODEM
100pF 5kΩ
10µF
20kΩ
20kΩ
20kΩ
5V
0.1µF
1/4
OP492
RX GAIN ADJUST
20kΩ
50kΩ
0.1µF
RECEIVE
RXA
20kΩ
Figure 36. Universal Direct Access Arrangement for Telephone Line Interface
SINGLE-SUPPLY INSTRUMENTATION AMPLIFIER
A low cost, single-supply instrumentation amplifier can be built
as shown in Figure 37. The circuit uses two op amps to form a
high input impedance differential amplifier. Gain can be set by
selecting resistor RG, which can be calculated using the transfer
function equation. Normally, VREF is set to 0 V. Then the output
voltage is a function of the gain times the differential input
voltage. However, the output can be offset by setting VREF from
0 V to 4 V, as long as the input common-mode voltage of the
amplifier is not exceeded.
5V
58
V_IN
1/2 7
OP292
V_OUT
1/2 1
4
OP292
V_REF
20kΩ
5kΩ
5kΩ
20kΩ
R_G
V_OUT =
5+
40kΩ
R_G
+ V_REF
Figure 37. Single-Supply Instrumentation Amplifier
In this configuration, the output can swing to near 0 V;
however, be careful because the common-mode voltage range of
the input cannot operate to 0 V. This is because of the limitation
of the circuit configuration where the first amplifier must be able to
swing below ground to attain a 0 V common-mode voltage,
which it cannot do. Depending on the gain of the instrumentation
amplifier, the input common-mode extends to within about 0.3 V
of zero. The worst-case common-mode limit for a given gain
can be easily calculated.
DAC OUTPUT AMPLIFIER
The OP292/OP492 are ideal for buffering the output of single-
supply DACs. Figure 38 shows a typical amplifier used to buffer
the output of a CMOS DAC that is connected for single-supply
operation. To do that, the normally current output 12-bit CMOS
DAC (R-2R ladder type) is connected backward to produce a
voltage output. This operating configuration necessitates a low
voltage reference. In this case, a 1.235 V low power reference is
used. The relatively high output impedance (10 kΩ) is buffered
by the OP292, and at the same time, gained up to a much more
usable level. The potentiometer provides an accurate gain trim
for a 4.095 V full-scale, allowing 1 mV increment per LSB of
control resolution.
The DAC8043 device comes in an 8-lead PDIP package, providing
a cost-effective, compact solution to a 12-bit analog channel.
5V
5V
5V
DAC8043
7.5kΩ
1 VREF
VD_{DD 8}
NC 2 ^RFB
CLCKlk 7
1.235V _{3 IOUT}
SSRrIi 6
AD589
4 GND
LD 5
1/2
OP292
20kΩ
8.45kΩ
500kΩ
V_OUT
1mV/LSB
0V – 4.095V
FS
LD SRI CLK
DIGITAL
CONTROL
Figure 38. 12-Bit Single-Supply DAC with Serial Bus Control
Rev. C | Page 14 of 20