Data Sheet

AD8338

Rev. 0 | Page 15 of 16

APPLICATIONS INFORMATION

The excellent performance of the AD8338 results in a flat response

over various gains with rail-to-rail output signal swing, high drive

capability, and a very high dynamic range at a low 12 mW. These

features make the AD8338 an exceptional choice for use in battery-

operated equipment, low frequency and baseband applications,

and many other applications.

SIMPLE ON-OFF KEYED (OOK) RECEIVER

For low complexity, low power data communications, a simple

link built using a modulating carrier tone in an on/off state

provides a fast and cost-effective solution to the designer. Such

designs are used in a variety of applications, including near-field

communications among noninterference mechanical systems,

low data rate sensors, RFID tags, and so on.

The schematic shown in Figure 45 demonstrates a complete

inductive telemetry on-off keyed (OOK) front end. The crystal

is cut for the target receive frequency of interest, creating a very

narrow-band filter, typically around the 6.78 MHz ISM band.

The AD8338 amplifies the signal (the gain is set by an external

controller) and drives a full-wave rectifier bridge. The output of

this bridge is then low-pass filtered into 100 Ω terminations. This

design provides excellent rejection of RF and excellent baseband

information recovery for the decision stage that follows.

The reactive filter components—Capacitors C1 through C4 and

Inductors L1 and L2—set the baseband recovery performance. A

design trade-off exchanges baseband response for RF attenuation.

Table 7 provides typical values for these components at two data

rates. Note that Capacitors C1 through C4 are all of equal value,

and Inductor L2 has the same value as L1.

Table 7. Typical Values for Components in Reactive Filter

Data Rate

C1 to C4

L1 and L2

Carrier Attenuation,

f = 6.78 MHz

19,200 bps

12 nF

240 µH

−101 dB

57,600 bps

3.9 nF

82 µH

−73 dB

INTERFACING THE AD8338 TO AN ADC

The AD8338 is well suited to drive a high speed analog-to-digital

converter (ADC) and is compatible with many ADCs from Analog

Devices, Inc. This example illustrates the interfacing of the AD8338

to the AD7451. The AD7451 is a low power, 3.0 V ADC, which

is also competitively priced for a low cost total solution.

Figure 46 shows the basic connections between the AD8338

and the AD7451. The common-mode voltage provided by the

AD8338 is within the specifications of the AD7451.

The AD8338 can be coupled directly to the AD7451 for full

dc-to-18 MHz operation at the highest level of performance with

low operating power (160 mW typical). The glueless interface

enables a physically small, high performance data acquisition

system that is ideal for many field instruments. A filter before

the VGA provides the antialiasing function and noise limiting.

In applications where the modulated information is not encoded

in the signal amplitude, use the AGC feature of the AD8338 to

reduce any bit errors in the sampled signal.

VREF

MODE

VREF

OUTP

OUTM

CRYSTAL

U1

AD8338

C6

0.01µF

GAIN

3.0V

INPR

INMR

C5

0.1µF

D1

D2

D4

D3

C1

C3

C2

C4

L1

L2

R1

100Ω

R2

100Ω

OOK_P

OOK_M

Figure 45. Complete, Low Power OOK Receiver

VREF

MODE

VREF

OUTP

OUTM

U1

AD8338

FILTER

OUTPUT

3.0V

3.0V

INPR

INMR

C3

0.1µF

SCLK

GND

AD7451

C1

0.1µF

C2

0.1µF

SDATA

CS

R1

49.9Ω

TO

MICRO-

CONTROLLER

Figure 46. Basic Connections to the AD7451 ADC