MAX2511EEI Maxim Integrated Products, MAX2511EEI Datasheet - Page 11

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

output is buffered and converted to a single-ended cur-
rent output at the MIXOUT pin, which can drive a shunt-
terminated bandpass filter over a large dynamic range.
MIXOUT can drive a shunt-terminated 330
load) to more than 2Vp-p over the entire supply range.
The signal passes through an external IF bandpass fil-
ter into the limiter input (LIMIN). LIMIN is a single-
ended input that is centered around the VREF pin
voltage. Open-circuit input impedance is typically
greater than 10k terminated to VREF. For proper oper-
ation, LIMIN must be tied to VREF through the filter ter-
minating impedance (not more than 1k
provides a constant output level, which is largely inde-
pendent of the limiter input-signal level over an 80dB
input range.
The adjustable output level allows easy interfacing of
the limiter output to the downstream circuitry. The lim-
iter’s output drives a variable-gain amplifier that adjusts
the limited output level from 0Vp-p to typically 1Vp-p as
the GC pin voltage is adjusted from 0.5V to 2.0V. Using
this feature allows the downstream circuitry, such as an
analog-to-digital converter (ADC), to run at optimum
performance by steering the limiter’s output level to
match the desired ADC input level. GC is also used for
transmit (Tx) gain adjustment in Tx mode, so be sure to
keep the voltage at an appropriate value for each mode.
The RSSI output provides a linear indication of the
received power level on the LIMIN input. The RSSI
monotonic dynamic range exceeds 90dB while provid-
ing better than 80dB linear range. The RSSI output
pulses current into an external filter capacitor (typically
100pF). The output is internally terminated with 6k
GND, and this R-C time constant sets the decay time.
The image-reject upconverter mixer operates in a fash-
ion similar to the downconverter mixer. The transmit
mixer consists of an input buffer amplifier that drives
on-chip IF phase shifters. The shifted signals are then
input to a pair of double-balanced mixers, which are
driven with the same quadrature (Q) LO source used
by the receiver. The mixer outputs are summed togeth-
er, largely canceling the image signal component. The
image-canceled signal from the mixer outputs is fed
through a variable-gain amplifier (VGA) with 40dB of
gain-adjust range.
The VGA output is connected to a driver amplifier with
an output 1dB compression point of 2dBm. The output
power can be adjusted from approximately 2dBm
Received-Signal-Strength Indicator
______________________________________________________________________________________
Transmitter
. The limiter
filter (165
Limiter
Low-Voltage IF Transceiver
to
to less than -40dBm by controlling the GC pin. For
output levels between -10dBm and -40dBm, -40dBc
IM3 levels are maintained. The resulting signal appears
as a differential output on TXOUT and TXOUT, which
expect a 100Ω differential load impedance.
TXOUT and TXOUT are open-collector outputs and
need external pull-up inductors to V
ation. They also need a DC block so the load does not
affect DC biasing. A shunt resistor across TXOUT,
TXOUT can be used to back-terminate an external filter,
as shown in the Typical Operating Circuit . It is possible
to use the receiver inputs RXIN and RXIN to provide
this termination, as described in the Filter Sharing sec-
tion. For single-ended operation, tie the unused input to
V
The on-chip LO requires only an external LC tank circuit
for operation. The tank circuit is connected across
TANK and TANK. A dual varactor diode is typically used
to adjust the frequency in a phase-locked loop (PLL).
See the Applications Information section for the tank cir-
cuit design equations. Keep the resonator’s Q as high
Figure 2. Simplified Oscillator Equivalent Circuit
CC
with Limiter and RSSI
.
Local Oscillator and Oscillator Buffer
V
CC
CC
for proper oper-
VBIAS
11