antenna can be long parallel wires spaced about 7.2cm

apart, with equal but opposite currents. Radio waves

from this antenna are detectable when the receiver is

brought within close proximity, but cancel out at greater

distances.

Infrared Receiver Front End for

Remote Controls and Data Links

The circuit in Figure 9 uses the MAX9003 as a PIN pho-

todiode preamplifier and discriminator for an infrared

receiver. The op amp is configured as a Delyiannis-

noise and eliminates low-frequency interference from

sunlight, fluorescent lights, etc. This circuit is applica-

ble for TV remote controls and low-frequency data links

up to 200kbps. Carrier frequencies are limited to

around 100kHz, as in the example circuit. Component

layout and routing for the amplifier should be tight to

reduce stray capacitance, 60Hz interference, and RFI

from the comparator. Crosstalk from comparator edges

distorts the amplifier signal. To minimize this effect, add

a lowpass RC filter to the connection from the reference

to the op amp’s noninverting input.

Signal Conditioning

For incoming signals that require filtering, the internal

amplifier provides an opportunity to create an active fil-

ter. This may be required for relatively high-speed sig-

nals that require adequate filtering of high-speed

carrier frequencies, harmonics, and external noise. In

addition, the amplifier can be used to amplify the signal

prior to digitizing it through the comparator to improve

the comparator’s overall output response and improve

its noise immunity.

Low-Power, High-Speed, Single-Supply

Op Amp + Comparator + Reference ICs

16

______________________________________________________________________________________

REF

0.1

µF

0.1

µF

1

2

100k

1.230V

COMP

AMP

C2

15pF, 5%

100kHz,

5Vp-p

C1

150pF,

5%

NEC

PH302B

NEC

SE307-C

51

Ω

49.9k

1%

4.99k

1%

R2

100k,

1%

LAYOUT-SENSITIVE AREA

MAX9003

R1 x C1 = R2 x C2 =

4.99k

Figure 9. Infrared Receiver Application