AD8338

Data Sheet

Rev. B | Page 18 of 19

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 20 mW of

quiescent power at maximum gain. 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 49 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 (Capacitor C1 through

Capacitor C4, Inductor L1, and Inductor 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 Capacitor C1 through Capacitor C4 are all of

equal value, and Inductor L2 has the same value as Inductor 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

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 49. Complete, Low Power OOK Receiver