AD8517/AD8527

–11–

REV. B

Table III. Snubber Network Values for Large Capacitive Loads

Rx

Cx

680 pF

300

Ω

3 nF

1 nF

100

Ω

10 nF

10 nF

400

Ω

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

≥ 1.8 V in a noninverting configuration with a

gain of 1. In an inverting configuration, the noise is 0.003% for

FREQUENCY – Hz

0.01

0.0001

10

20k

0.001

0.1

1

100

1k

10k

Figure 26. THD + N vs. Frequency Graph

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 M

Ω 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.

AD8517

10k

0.022 F

0.9V TO 2.5V

1 F

1 F

1M

1.8V TO 5V

100

1M

Figure 27. A Micropower Reference Voltage Generator

MICROPHONE PREAMPLIFIER

The AD8517 is ideal to use as a microphone preamplifier.

Figure 28 shows this implementation.

R3

220k

C1

0.1 F

R1

2.2k

ELECTRET

MIC

AD8517

R2

22k

R3

R2

Figure 28. A Microphone Preamplifier

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

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.

6.2V

6.2V

TRANSMIT

TxA

RECEIVE

RxA

C1

0.1 F

R1

10k

R2

9.09k

2k

P1

Tx GAIN

ADJUST

A1

R3

360

1:1

T1

TO

TELEPHONE

LINE

1

2

3

7

6

5

2

3

1

6

5

7

10 F

R7

10k

R8

10k

R5

10k

R6

10k

R9

10k

R14

14.3k

R10

10k

R11

10k

R12

10k

R13

10k

C2

0.1 F

P2

Rx GAIN

ADJUST

2k

600

+1.8V DC

MIDCOM

671-8005

A2

A3

A4

1/2

AD8517

1/2

AD8517

1/2

AD8527

1/2

AD8527

Figure 29. A Single-Supply Direct Access Arrangement

for Modems