Table 2. RXIN or
RXIN
Input Impedance
Rec eive IF Filter
The interstage filter, located between the MIXOUT pin
and the LIMIN pin, is typically a three-terminal, 330
,
10.7MHz bandpass filter. This filter prevents the limiter
from acting on any undesired signals that are present
at the mixer’s output, such as LO feedthrough, out-of-
band channel leakage, and spurious mixer products.
The filter connections are also set up to feed DC bias
from VREF into LIMIN and MIXOUT through two 330
filter-termination resistors. (See the Typical Operating
Circuitfor more information).
T ransmit Output Matc hing
The transmit outputs, TXOUT and
TXOUT
, are open-
collector outputs and therefore present a high
impedance.
For differential drive, TXOUT and
TXOUT
are connected
to V
CC
via chokes, and each side is AC coupled to the
load. A terminating resistor between TXOUT and
TXOUT
sets the output impedance. This resistor pro-
vides a stable means of matching to the load.
TXOUT and
TXOUT
are voltage-swing limited, and
therefore cannot drive the specified maximum power
across more than 150
load impedance. This load
impedance typically consists of a shunt-terminating
resistor in parallel with a filter load impedance. To drive
higher output load impedances, the gain must be
reduced (via the GC pin) to avoid saturating the TX out-
put stage.
For single-ended applications, connect the unused TX
output output pin directly to V
CC
.
400MHz IS M Applic ations
The MAX2510 can be used as a front-end IC in appli-
cations where the RF carrier frequency is in the
400MHz ISM band. In this case, Maxim recommends
preceding the MAX2510 receiver section with a low-
noise amplifier (LNA) that can operate over the same
supply voltage range. The MAX2630–MAX2633 family
of amplifiers meets this requirement. In many applica-
tions, the MAX2510’s transmit output power is sufficient
to eliminate the need for an external power amplifier.
______________________Layout Issues
A well-designed PC board is an essential part of an RF
circuit. Use the MAX2510 evaluation kit and the recom-
mendations below as guides to generate your own
layout.
Power-S upply Layout
A star topology, which has a heavily decoupled central
V
CC
node, is the ideal power-supply layout for minimiz-
ing coupling between different sections of the chip. The
V
CC
traces branch out from this node, each going to
one V
CC
connection in the MAX2510 typical operating
circuit. At the end of each of these traces is a bypass
capacitor that presents low impedance at the RF fre-
quency of interest. This method provides local decou-
pling at each V
CC
pin. At high frequencies, any signal
leaking out of a supply pin sees a relatively high imped-
ance (formed by the V
CC
trace impedance) to the cen-
tral V
CC
node, and an even higher impedance to any
other supply pin, minimizing Vcc supply-pin coupling.
A single ground plane suffices. Where possible, multi-
ple parallel vias aid in reducing inductance to the
ground plane.
Place the VREF decoupling capacitor (0.1μF typical) as
close to the MAX2510 as possible for best interstage fil-
ter performance. For best results, use a high-quality,
low-ESR capacitor.
Matching/biasing networks around the receive and
transmit pins should be symmetric and as close to the
chip as possible. A cutout in the ground plane under
the matching network components can be used to
reduce parasitic capacitance.
Decouple pins 19 and 21 (V
CC
) directly to pin 20 (Rx,
Tx ground), which should be directly connected the
ground plane. Similarly, decouple pin 8 directly to pin 7.
Refer to the Pin Description table for more information.
M
Low-Voltage IF Transc eiver with
Limiter/RS S I and Quadrature Modulator
______________________________________________________________________________________
11
64 - j109
53 - j87
94 - j143
149 - j184
SERIES IMPEDANCE
(
)
275 - j203
400
500
300
200
FREQUENCY
(MHz)
100