AD8517 Analog Devices, AD8517 Datasheet - Page 11

• Manufacturer Part Number: AD8517
• Description: Low Voltage, High Slew Rate, Low Noise, 7 MHZ Rail-to-rail op Amp, Single
• Manufacturer: Analog Devices

C
680 pF
1 nF
10 nF
TOTAL HARMONIC DISTORTION + NOISE
The AD85x7 family offers a low total harmonic distortion, which
makes this amplifier ideal for audio applications. Figure 26 shows a
graph of THD + N, for a V
and 0.03% for V
gain of 1. In an inverting configuration, the noise is 0.003% for
all V
A MICROPOWER REFERENCE VOLTAGE GENERATOR
Many single supply circuits are configured with the circuit-biased
to one-half of the supply voltage. In these cases, a false-ground
reference can be created by using a voltage divider buffered by an
amplifier. Figure 27 shows the schematic for such a circuit.
The two 1 MΩ resistors generate the reference voltages while
drawing only 0.9 µA of current from a 1.8 V supply. A capacitor
connected from the inverting terminal to the output of the op
amp provides compensation to allow for a bypass capacitor to be
connected at the reference output. This bypass capacitor helps
establish an ac ground for the reference output.
Table III. Snubber Network Values for Large Capacitive Loads
LOAD
SY
.
0.0001
1M
1M
0.001
0.01
0.1
1
10
V
A
V
S
V
S
S
1 F
> 3V TO 5V
= +2
= 1.8V
≥ 1.8 V in a noninverting configuration with a
Rx
300 Ω
100 Ω
400 Ω
AD8517
1.8V TO 5V
100
S
0.022 F
> 3 V the THD + N is about 0.001%
10k
FREQUENCY – Hz
100
1k
Cx
3 nF
10 nF
30
1 F
nF
V
0.9V TO 2.5V
REF
10k
20k
MICROPHONE PREAMPLIFIER
The AD8517 is ideal to use as a microphone preamplifier.
Figure 28 shows this implementation.
R1 is used to bias an electret microphone and C1 blocks dc
voltage from the amplifier. The magnitude of the gain of the
amplifier is approximately R3/R2 when R2 ≥ 10 × R1. V
should be equal to 1/2 1.8 V for maximum voltage swing.
Direct Access Arrangement for Telephone Line Interface
Figure 28 illustrates a 1.8 V transmit/receive telephone line
interface for 600 Ω transmission systems. It allows full duplex
transmission of signals on a transformer-coupled 600 Ω line in a
differential manner. Amplifier A1 provides gain that can be ad-
justed to meet the modem output drive requirements. Both A1
and A2 are configured to apply the largest possible signal on a
single supply to the transformer. Amplifier A3 is configured as a
difference amplifier 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. 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 arrays. Couple this with the AD8517/AD8527’s 5-lead
SOT-23, 8-lead MSOP, and 8-lead SOIC footprint and this
circuit offers a compact solution.
TELEPHONE
600
LINE
Z
TO
O
MIDCOM
671-8005
ELECTRET
1:1
T1
10k
2.2k
R11
MIC
10k
V
6.2V
6.2V
R1
IN
R12
V
CC
360
R9
10k
2
3
0.1 F
R3
C1
10k
A3
R10
AD8527
AD8517
10k
1/2
22k
Tx GAIN
ADJUST
AD8517
R5
R2
V
1
1/2
7
1
REF
1/2
P1
2k
10k
A2
A1
10k
R6
R13
9.09k
AD8517/AD8527
AD8517
R2
2
3
6
5
220k
14.3k
6
5
V
R3
R14
CC
A4
10k
AD8527
R1
Rx GAIN
ADJUST
|
10 F
2k
A
1/2
V
P2
7
+1.8V DC
|
=
R3
R2
0.1 F
0.1 F
R7
10k
R8
10k
C1
C2
V
OUT
TRANSMIT
TxA
RECEIVE
RxA
REF