Datasheet

AD8338 Data Sheet
Rev. A | Page 18 of 20
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 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—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
Figure 49. Complete, Low Power OOK Receiver
VREF
MODE
VREF
OUTP
OUTM
COMM
OFSN
CRYSTAL
ANTENNA
C
TUNE
U1
AD8338
C6
0.01µF
GAIN
3.0V
INPR
INMR
DETO
C5
0.1µF
D1 D2
D4 D3
C1
C3
C2
C4
L1
L2
R1
100Ω
R2
100Ω
OOK_P
OOK_M
11279-048