MAX7033EUI+T Maxim Integrated Products, MAX7033EUI+T Datasheet - Page 10

• Manufacturer Part Number: MAX7033EUI+T
• Description: RF Receiver IC RX 315MHZ/433MHZ ASK
• Manufacturer: Maxim Integrated Products
• Type: Receiverr

Specifications of MAX7033EUI+T

• Package / Case: TSSOP-28
• Operating Frequency: 450 MHz
• Operating Supply Voltage: 3.3 V, 5 V
• Maximum Operating Temperature: + 105 C
• Minimum Operating Temperature: - 40 C
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

315MHz/433MHz ASK Superheterodyne
Receiver with AGC Lock
The off-chip inductive degeneration is achieved by
connecting an inductor from LNASRC to AGND. This
inductor sets the real part of the input impedance at
LNAIN, allowing for a more flexible input impedance
match, such as a typical PCB trace antenna. A nominal
value for this inductor with a 50Ω input impedance is
15nH, but is affected by PCB trace.
The LC tank filter connected to LNAOUT comprises L3
and C2 (see the Typical Application Circuit ). Select L3
and C2 to resonate at the desired RF input frequency.
The resonant frequency is given by:
where:
L
C
L
capacitance of the PCB traces, package pins, mixer
input impedance, LNA output impedance, etc. These
parasitics at high frequencies cannot be ignored, and
can have a dramatic effect on the tank filter center fre-
quency. Lab experimentation should be done to opti-
mize the center frequency of the tank.
When the AC pin is low, the automatic gain-control
(AGC) circuit monitors the RSSI output. As the RSSI
output reaches 1.98V, which corresponds to RF input
level of -62dBm, the AGC switches on the LNA gain
Figure 1. AGC Lock Activation Cycles
10
TOTAL
PARASITICS
TOTAL
AC PIN
______________________________________________________________________________________
SHDN
PIN
= L3 + L
= C2 + C
f
RF
V
and C
V
IH
IL
=
PARASITICS
PARASITICS
V
V
2π
LOCK
IH
IL
AGC
PARASITICS
L
TOTAL
Automatic Gain Control
.
UNLOCK
.
AGC
1
AGC ENABLED
×
include inductance and
C
TOTAL
LOCK
AGC
UNLOCK
AGC
reduction resistor. The resistor reduces the LNA gain
by 35dB, thereby reducing the RSSI output by about
500mV. The LNA resumes high-gain mode when the
RSSI level drops back below 1.39V (approximately
-70dBm at RF input) for 1ms. The AGC has a hysteresis
of 8dB. With the AGC function, the MAX7033 can reli-
ably produce an ASK output for RF input levels up to
0dBm with modulation depth of 18dB.
When the AC pin is high and SHDN goes high, the
AGC circuit is disabled and the LNA is always in high-
gain mode. The AGC function can be resumed by
bringing the AC pin low when SHDN is high.
The MAX7033 features an AGC lock function that is
asserted when the level at the AC pin transitions from
low to high while SHDN is high. Locking the AGC locks
the LNA in the current gain state. As shown in Figure 1,
the AGC lock function can be enabled or disabled as
long as the SHDN pin is high. Changing the state of AC
when SHDN is low has no effect.
A unique feature of the MAX7033 is the integrated
image rejection of the mixer. This device eliminates the
need for a costly front-end SAW filter for most applica-
tions. Advantages of not using a SAW filter are
increased sensitivity, simplified antenna matching, less
board space, and lower cost.
The mixer cell is a pair of double balanced mixers that
perform an IQ downconversion of the RF input to the
10.7MHz IF from a low-side injected LO (i.e., f
f
signals to achieve 44dB of image rejection. Low-side
EFFECT
IF
NO
). The image-rejection circuit then combines these
DISABLED
AGC
EFFECT
NO
ENABLED
AGC
EFFECT
NO
DISABLED
AGC
LO
Mixer
= f
RF
-