315MHz/433MHz ASK Superheterodyne

Receiver with AGC Lock

______________________________________________________________________________________

11

COMPONENT

DESCRIPTION

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

L1

56nH

120nH

TOKO LL1608-FH

L2

15nH

15nH

Murata LQP11A

L3

15nH

27nH

Murata LQP11A

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

375MHz) when it is left unconnected, thereby eliminating

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:

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

ff

M

REF

RF

IF

=

×

-

32

Table 1. Component Values for Typical Application Circuit