OP450GRU AD [Analog Devices], OP450GRU Datasheet - Page 13

• Manufacturer Part Number: OP450GRU
• Description: CMOS Single-Supply Rail-to-Rail Input/Output Operational Amplifiers
• Manufacturer: AD [Analog Devices]

REV. 0
Headphone Driver
The audio signal is coupled into each input through a 10 F ca-
pacitor. This large value insures the resulting high pass filter
cutoff is below 20 Hz, preserving full audio fidelity. If the input
already has the proper dc bias, then the coupling capacitor and
biasing resistors are not required. A 270 F capacitor is used at
the output to couple the amplifier to the headphone speaker.
This value is much larger than the input capacitor because of
the low impedance of the headphones, which can range from
32
series with the output capacitor to protect the op amp’s output
in the event the output accidentally becomes shorted to ground.
INPUT
RIGHT
INPUT
LEFT
Figure 37. A Single-Supply Stereo Headphone Driver
to 600
0.001
0.01
10 F
10 F
0.1
50k
50k
50k
50k
1
20
+V + 5V
+V
V
A
V
SY
V
IN
100k
100k
or more. An additional 20
= +1
= 300mV rms
Figure 38. THD vs. Frequency
=
2.5V
10 F
10 F
100
OP250
OP250
+V + 5V
1/2
1/2
FREQUENCY – Hz
1 F/0.1 F
1k
20
20
R
270 F
270 F
L
= 500
resistor is used in
50k
50k
R
L
R
L
= 2k
10k
10k
HEADPHONE
HEADPHONE
20k
RIGHT
LEFT
–13–
Direct Access Arrangement for Modems
Figure 39 illustrates a +5 V transmit/receive telephone line inter-
face for 600
nals on a transformer coupled 600
Amplifier A1 provides gain which can be adjusted to meet the
modem output drive requirements. Both A1 and A2 are config-
ured so as to apply the largest possible signal on a single supply to
the transformer. Because of the OP450’s high output current
drive and low dropout voltages, the largest signal available on a
single +5 V supply is approximately 4.5 V p-p into a 600
mission system. Amplifier A3 is configured as a difference ampli-
fier for two reasons: (1) It prevents the transmit signal from
interfering with the receive signal and (2) it extracts the receive
signal from the transmission line for amplification by A4. Ampli-
fier A4’s gain can be adjusted in the same manner as A1’s to meet
the modem’s input signal requirements. Standard resistor values
permit the use of SIP (Single In-line Package) format resistor ar-
rays. Couple this with the OP450 14-lead TSSOP or SOIC foot-
print and this circuit offers a compact, cost-effective solution.
Figure 39. A Single-Supply Direct Access Arrangement for
Modems
600
TO TELEPHONE
A1, A2, A3, A4 = 1/4 OP450
Z
O
LINE
MIDCOM
671-8005
1:1
T1
6.2V
6.2V
systems. It allows full duplex transmission of sig-
10k
R11
10k
10k
R9
R12
360
R3
2
3
10k
10k
10k
A3
R10
R5
R6
TX GAIN
ADJUST
P1
2k
1
1
7
10k
A1
A2
R13
line in a differential manner.
9.09k
OP250/OP450
R2
6
2
3
5
14.3k
6
5
R14
A4
10k
R1
RX GAIN
ADJUST
10 F
2k
0.1 F
7
P2
C1
+5V DC
0.1 F
C2
R7
10k
R8
10k
TRANSMIT
RECEIVE
trans-
RXA
TXA