MAX9000–MAX9005
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
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