OP462_15 Datasheet, PDF (16/20 Pages) Analog Devices – 15 MHz Rail-to-Rail Operational Amplifiers

OP162/OP262/OP462
APPLICATIONS CIRCUITS
SINGLE-SUPPLY STEREO HEADPHONE DRIVER
Figure 43 shows a stereo headphone output amplifier that can
operate from a single 5 V supply. The reference voltage is
derived by dividing the supply voltage down with two 100 kΩ
resistors. A 10 µF capacitor prevents power supply noise from
contaminating the audio signal and establishes an ac ground for
the volume control potentiometers.
The audio signal is ac-coupled to each noninverting input
through a 10 µF capacitor. The gain of the amplifier is con-
trolled by the feedback resistors and is (R2/R1) + 1. For this
example, the gain is 6. By removing R1, the amplifier would
have unity gain. To short-circuit protect the output of the
device, a 169 Ω resistor is placed at the output in the feedback
network. This prevents any damage to the device if the head-
phone output becomes shorted. A 270 µF capacitor is used at
the output to couple the amplifier to the headphone. This value
is much larger than that used for the input because of the low
impedance of headphones, which can range from 32 Ω to 600 Ω
or more.
R1 = 10kΩ
R2 = 50kΩ
10µF
LEFT IN
10µF
L VOLUME
CONTROL
10kΩ
5V
5V
OP262-A
169Ω
270µF
47kΩ
HEADPHONE
LEFT
100kΩ
100kΩ
10µF
5V
10kΩ
RIGHT IN
10µF
R VOLUME
CONTROL
OP262-B
169Ω
270µF
47kΩ
R2 = 50kΩ
HEADPHONE
RIGHT
R1 = 10kΩ
10µF
Figure 43. Headphone Output Amplifier
Data Sheet
INSTRUMENTATION AMPLIFIER
Because of their high speed, low offset voltages, and low noise
characteristics, the OP162/OP262/OP462 can be used in a wide
variety of high speed applications, including precision instru-
mentation amplifiers. Figure 44 shows an example of such an
application.
–V_IN
OP462-A
2kΩ
1kΩ
2kΩ
OP462-D
+V_IN
R_{G 1kΩ}
10kΩ
OP462-C
2kΩ
10kΩ
OP462-B
1.9kΩ
200Ω
10 TURN
(OPTIONAL)
OUTPUT
Figure 44. High Speed Instrumentation Amplifier
The differential gain of the circuit is determined by RG, where
A_DIFF
= 1+
2
R_G
with the RG resistor value in kΩ. Removing RG sets the circuit
gain to unity.
The fourth op amp, OP462-D, is optional and is used to
improve CMRR by reducing any input capacitance to the
amplifier. By shielding the input signal leads and driving the
shield with the common-mode voltage, input capacitance is
eliminated at common-mode voltages. This voltage is derived
from the midpoint of the outputs of OP462-A and OP462-B by
using two 10 kΩ resistors followed by OP462-D as a unity-gain
buffer.
It is important to use 1% or better tolerance components for the
2 kΩ resistors, as the common-mode rejection is dependent on
their ratios being exact. A potentiometer should also be connected
in series with the OP462-C noninverting input resistor to ground
to optimize common-mode rejection.
The circuit in Figure 44 was implemented to test its settling
time. The instrumentation amp was powered with −5 V, so the
input step voltage went from −5 V to +4 V to keep the OP462
within its input range. Therefore, the 0.05% settling range is
when the output is within 4.5 mV. Figure 45 shows the positive
slope settling time to be 1.8 µs, and Figure 46 shows a settling
time of 3.9 µs for the negative slope.
Rev. H | Page 16 of 20