AD822
3 V, SINGLE-SUPPLY STEREO HEADPHONE
DRIVER
The AD822 exhibits good current drive and THD + N
performance, even at 3 V single supplies. At 1 kHz, total
harmonic distortion plus noise (THD + N) equals –62 dB
(0.079%) for a 300 mV p-p output signal. This is comparable to
other single-supply op amps that consume more power and
cannot run on 3 V power supplies.
3V
1µF
MYLAR
CHANNEL 1
47.5kΩ
+
that all signals in the audio frequency range (20 Hz to 20 kHz) are
delivered to the headphones.
LOW DROPOUT BIPOLAR BRIDGE DRIVER
The AD822 can be used for driving a 350 Ω Wheatstone bridge.
AD589, a 1.235 V low power reference. The output of 4.5 V can
be used to drive an ADC converter front end. The other half of
the AD822 is configured as a unity gain inverter and generates
the other bridge input of −4.5 V. Resistor R1 and Resistor R2
provide a constant current for bridge excitation. The AD620 low
power instrumentation amplifier is used to condition the
differential output voltage of the bridge. The gain of the AD620 is
programmed using an external resistor RG and determined by
G
=
49.9
k
Ω
R
G
+
1
+V
S
95.3kΩ
3
2
8
0.1µF
1
500µF
0.1µF
+
–
AD822
1/2
4.99kΩ
95.3kΩ
L
10kΩ
HEADPHONES
32Ω IMPEDANCE
10kΩ
4.99kΩ
6
1µF
MYLAR
CHANNEL 2
47.5kΩ
5
R
49.9kΩ
+1.235V
3
8
AD822
+
4
1/2
7
00874-050
1/2
+
AD589
AD822
2
–
–
500µF
25.4kΩ 1%
10kΩ 1%
+
R1
20Ω
1
TO A/D CONVERTER
REFERENCE INPUT
Figure 50. 3 V Single-Supply Stereo Headphone Driver
350Ω
10kΩ 1%
350Ω
R
G
10kΩ 1%
–V
S
1µF
–5V
Figure 51. Low Dropout Bipolar Bridge Driver
Rev. G | Page 23 of 28
00874-051
+
5
–
In Figure 50, each channel’s input signal is coupled via a 1 μF
Mylar capacitor. Resistor dividers set the dc voltage at the non-
inverting inputs so that the output voltage is midway between the
power supplies (1.5 V). The gain is 1.5. Each half of the AD822
can then be used to drive a headphone channel. A 5 Hz high-pass
filter is realized by the 500 μF capacitors and the headphones that
can be modeled as 32 Ω load resistors to ground. This ensures
2
6
AD822
4
1/2
7
–4.5V
R2
20Ω
+V
S
0.1µF
GND
+
0.1µF
–V
S
+
–
–
+V
S
350Ω
350Ω
3
7
6
AD820
4
5
V
REF
–V
S
+
+
+
+5V
1µF
AD [ ANALOG DEVICES ]
