Rainbow Electronics MAX7033 - Manual (Page 11)

MAX7033
315MHz/433MHz ASK Superheterodyne
Receiver with AGC Lock
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COMPONENT VALUE FOR f RF = 433MHz VALUE FOR f RF = 315MHz DESCRIPTION
L1 56nH 120nH TOKO LL1608-FH
L2 15nH 15nH Murata LQP11A
L3 15nH 27nH Murata LQP11A
C1 100pF 100pF 5%
C2 2pF 4pF ± 0.1pF
C3 100pF 100pF 5%
C4 100pF 100pF 5%
C5 1500pF 1500pF 10%
C6 220pF 220pF 5%
C7 470pF 470pF 5%
C8 0.47µF 0.47µF 20%
C9 220pF 220pF 10%
C10 0.01µF 0.01µF 20%
C11 0.01µF 0.01µF 20%
C12 15pF 15pF Depends on XTAL
C13 15pF 15pF Depends on XTAL
R1 5.1k Ω 5.1k Ω 5%
X1 6.5984MHz 4.7547MHz —
X2 10.7MHz ceramic filter 10.7MHz ceramic filter Murata SFECV10.7 series
injection is required due to the on-chip image-rejection
architecture. The IF output is driven by a source follow-
er biased to create a driving-point impedance of 330
Ω;
this provides a good match to the off-chip 330 Ω ceram-
ic IF filter.
The IRSEL pin is a logic input that selects one of the
three possible image-rejection frequencies. When V
IRSEL
= 0V, the image rejection is tuned to 315MHz. V IRSEL =
V DD5 / 2 tunes the image rejection to 375MHz, and
V IRSEL = V DD5 tunes the image rejection to 433MHz. The
IRSEL pin is internally set to V DD5 / 2 (image rejection at
375MHz) when it is left unconnected, thereby eliminating
the need for an external V
DD5 / 2 voltage.
Phase-Locked Loop
The PLL block contains a phase detector, charge
pump, integrated loop filter, VCO, asynchronous 64x
clock divider, and crystal oscillator driver. Besides the
crystal, this PLL does not require any external compo-
nents. The VCO generates a low-side LO. The relation-
ship between the RF, IF, and reference frequencies is
given by:
where:
M = 1 (V XTALSEL = V DD5 ) or 2 (V XTALSEL = 0V)
To allow the smallest possible IF bandwidth (for best sen-
sitivity), minimize the tolerance of the reference crystal.
Intermediate Frequency and RSSI
The IF section presents a differential 330 Ω load to pro-
vide matching for the off-chip ceramic filter. The six
internal AC-coupled limiting amplifiers produce an
overall gain of approximately 65dB, with a bandpass-fil-
ter-type response centered near the 10.7MHz IF fre-
quency with a 3dB bandwidth of approximately 10MHz.
The RSSI circuit demodulates the IF by producing a DC
output proportional to the log of the IF signal level, with
a slope of approximately 14.2mV/dB (see the Typical
Operating Characteristics).
Applications Information
Crystal Oscillator
The crystal oscillator in the MAX7033 is designed to
present a capacitance of approximately 3pF between
the XTAL1 and XTAL2. If a crystal designed to oscillate
with a different load capacitance is used, the crystal is
pulled away from its stated operating frequency, intro-
ducing an error in the reference frequency. Crystals
f
f f
M
REF
RF IF =
×
-
32
Table 1. Component Values for Typical Application Circuit