Datasheet

detector to dynamically follow peak changes of the data
filter output voltage. For faster receiver startup, the circuit
shown in Figure 3 can be used.
433.92MHz Band
The MAX1470 can be configured to receive ASK modu-
lated data with carrier frequency ranging from 250MHz
to 500MHz. Only a small number of components need to
be changed to retune the RF section to the desired RF
frequency.
Table 2 shows a list of changed components and their
values for a 433.92MHz RF; all other components remain
unchanged.
The integrated image rejection of the MAX1470 is specifi-
cally designed to function with a 315MHz input frequency
by attenuating any signal at 293.6MHz. The benefit of the
on-chip image rejection is that an external SAW filter is not
needed, reducing cost and the insertion loss associated
with SAW filters. The image rejection cannot be retuned
for different RF input frequencies and therefore is degrad-
ed. The image rejection at 433.92MHz is typically 39dB.
Layout Considerations
A properly designed PC board is an essential part of any
RF/microwave circuit. On high-frequency inputs and out-
puts, use controlled-impedance lines and keep them as
short as possible to minimize losses and radiation. At high
frequencies, trace lengths that are approximately 1/20 the
wavelength or longer become antennas. For example, a
2in trace at 315MHz can act as an antenna.
Keeping the traces short also reduces parasitic induc-
tance. Generally, 1in of a PC board trace adds about
20nH of parasitic inductance. The parasitic inductance
can have a dramatic effect on the effective inductance.
For example, a 0.5in trace connecting a 100nH inductor
adds an extra 10nH of inductance or 10%.
To reduce the parasitic inductance, use wider traces and
a solid ground or power plane below the signal traces.
Using a solid ground plane can reduce the parasitic induc-
tance from approximately 20nH/in to 7nH/in. Also, use low-
inductance connections to ground on all GND pins, and
place decoupling capacitors close to all V
DD
connections.
Figure 2. Generating Data Slicer Threshold Figure 3. Using PDOUT for Faster Startup
Table 2. Changed Component Values for
433.92MHz
Note: These values are affected by PC board layout.
COMPONENT VALUE FOR 433MHz RF
C9 1.0pF
L1 15nH
L2 56nH
Y1 6.6128MHz
25
C4
R1
20
DSN
19
DSP
MAX1470
DATA OUT
DATA
SLICER
DATA
FILTER
25
47nF
25kΩ
20
DSN
19
DSP
MAX1470
DATA OUT
DATA
SLICER
DATA
FILTER
26
PDOUT
250kΩ
47nF
MAX1470 315MHz Low-Power, +3V Superheterodyne
Receiver
www.maximintegrated.com
Maxim Integrated │ 9
Chip Information
TRANSISTOR COUNT: 1835
PROCESS: CMOS