MAX2511 View Datasheet(PDF) - Maxim Integrated

Part Name

Description

Manufacturer

MAX2511

Low-Voltage IF Transceiver with Limiter and RSSI

Maxim Integrated 

Low-Voltage IF Transceiver

with Limiter and RSSI

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 330Ω filter (165Ω

load) to more than 2Vp-p over the entire supply range.

Limiter

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 10kΩ terminated to VREF. For proper oper-

ation, LIMIN must be tied to VREF through the filter ter-

minating impedance (not more than 1kΩ). The limiter

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.

Received-Signal-Strength Indicator

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 6kΩ to

GND, and this R-C time constant sets the decay time.

Transmitter

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

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 VCC for proper oper-

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

VCC.

Local Oscillator and Oscillator Buffer

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

VCC

VBIAS

Figure 2. Simplified Oscillator Equivalent Circuit

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