MAX2511EEI Maxim Integrated Products, MAX2511EEI Datasheet - Page 12

• Manufacturer Part Number: MAX2511EEI
• Description: RF Transceiver IF Txr w/Limitr RSSI
• Manufacturer: Maxim Integrated Products

Low-Voltage IF Transceiver
with Limiter and RSSI
as possible for lowest phase noise. The tank’s PC board
layout is also critical to good performance (consult the
Layout Issues section for more information).
The OSCOUT pin buffers the internal oscillator signal
for driving an external PLL. This output should be AC
coupled and terminated at the far end (typically the
input to a prescaler) with a 50
level is desired, you can use a resistive termination up
to 100 . When a controlled-impedance PC board is
used, this trace’s impedance should match the termina-
tion impedance.
The MAX2511 features four power-supply modes to pre-
serve battery life. These modes are selected via the
RXEN and TXEN pins, according to Table 1.
In shutdown mode, all part functions are off. In standby
mode, the LO and the LO buffer are active. This allows
a PLL (implemented externally to the MAX2511) to
remain up and running, avoiding any delay resulting
from PLL loop settling. Transmit (Tx) mode enables the
LO circuitry, upconverter mixer, transmit VGA, and out-
put driver amplifier. Receive (Rx) mode enables the LO
circuitry, downconverter mixer, limiting amplifier, and
adjustable output level amplifier.
Table 1. Power-Supply Mode Selection
The MAX2511 can be used in applications where the
200MHz to 440MHz signal is an RF (rather than an IF)
signal, such as in 400MHz ISM applications. In this
case, we recommend preceding the MAX2511 receiver
section with a low-noise amplifier (LNA) that can oper-
ate over the same supply-voltage range. The
MAX2630–MAX2633 family of amplifiers meets this
requirement. But since these parts have single-ended
inputs and outputs, it is necessary to AC terminate the
unused MAX2511 input (RXIN) to ground with 47nF.
12
__________Applications Information
______________________________________________________________________________________
STATE
RXEN
High
High
Low
Low
400MHz ISM Applications
STATE
TXEN
High
High
Low
Low
Power Management
load. If a larger output
Shutdown
Transmit
Standby
Receive
MODE
The on-chip oscillator circuit requires a parallel reso-
nant tank circuit connected across TANK and TANK.
Figure 3 shows an example of an oscillator tank circuit.
Inductor L1 is resonated with the effective total capaci-
tance of C1 in parallel with the series combination of
C2, C3, and (CD1) / 2. CD1 is the capacitance of one
of the varactor diodes. Typically, C2 = C3 to maintain
symmetry. The effective parasitic capacitance, C
(including PCB parasitics), is approximately 3.5pF. The
total capacitance is given by the following equation:
Using this value for the resonant tank circuit, the oscil-
lation frequency is as follows:
Starting with the inductor recommended in Table 2,
choose the component values according to your appli-
cation needs, such as phase noise, tuning range, and
VCO gain. Keep the tank’s Q as high as possible to
reduce phase noise. For most of the MAX2511’s appli-
cations (such as a first IF to second IF transceiver), the
oscillator’s tuning range can be quite small, since the IF
frequencies are not tuned for channel selection. This
allows a narrowband oscillator tank to be used, which
typically provides better phase noise and stability per-
formance than wideband tank circuits. Careful PC
board layout of the oscillator tank is essential. See the
Layout Issues section for more information.
To overdrive the oscillator from an external 50Ω source,
see Figure 4.
The RXIN, RXIN port typically needs an impedance-
matching network for proper connection to external cir-
cuitry such as a filter. See the Typical Operating Circuit
for an example circuit topology. A shunt resistor across
RXIN, RXIN can be used to set terminating impedance,
with a slight degradation of the Noise Figure.
The component values used in the matching network
depend on the desired operating frequency as well as
the filter impedance. Table 3 indicates the RXIN, RXIN
differential input impedance in both series and parallel
form. This data is also plotted in the Typical Operating
Characteristics .
C
EFF
F
OSC
=
Rx Input Impedance Matching
EMBED Equation.2
C2
2
=
2
1
C
L C
2
D1
1
1 EFF
C1
Oscillator Tank
C
P
P