MRFIC2101 Ver la hoja de datos (PDF) - Motorola => Freescale

Número de pieza

componentes Descripción

Fabricante

MRFIC2101

900 MHz TX-Mixer/Exciter

Motorola => Freescale 

APPLICATIONS INFORMATION

DESIGN PHILOSOPHY

The MRFIC2101 was designed as a linear upconverter for

U.S. and Japan digital cellular radios. However, it is versatile

enough to be used in other applications such as analog

cellular, GSM, CDMA and the 900 MHz ISM band.

The mixer is double-balanced to minimize spurious and LO

emission. An external balun is required on the mixer RF output

to maximize linearity and maintain good balance. An

inexpensive and easy to implement balun is described below

in the theory of operation. The IF and LO ports do not require

baluns. The LO split is achieved on-chip with a buffer amplifier

which also reduces the LO power requirement. The IF port

can be driven differentially or single-ended with a decoupling

capacitor on the unused IF input. Baseband signals can be

applied directly to the IF inputs and the device becomes a

complete low–power transmitter.

To maximize efficiency in various systems, the exciter bias

current is externally adjustable. The bias current can also be

ramped to reduce spectral splatter.

To minimize current drain in TDD/TDMA systems, the

MRFIC2101 has separate TTL/CMOS compatible enable pins

for the mixer and the exciter.

THEORY OF OPERATION

Matching the LO port to 50 ohms can be done several

ways. The recommended approach is a series inductor as

close to the IC as possible. The inductor value is small enough

(~8 – 15 nH depending on LO frequency and distance from

the IC) to be printed on the board. A DC block is required

and should not be placed between the inductor and IC since

the added electrical length will cause a poor match.

The IF ports are approximately 250 ohms resistive in

parallel with 5.0 pF of capacitance. Matching directly into this

impedance is not recommended. Series 82 nH chip inductors

should first be placed as close to both IF ports as possible.

This presents a high impedance to the IF ports at the LO

frequency which substantially reduces the LO leakage out

of the RF port. The resulting impedance then may be

matched to the desired characteristic impedance. DC

blocking capacitors are also required.

Both RF ports are approximately 25 ohms resistive in

series with 1.5 pF of capacitance (or the parallel equivalent,

380 ohms in parallel with 1.9 pF). Best linearity is achieved

by loading each port with 100 ohms resistive and resonating

the 1.9 pF. Ideally, a half wavelength transmission line could

be used to combine the two differential RF ports into one;

however, the size of such a line would be very large. Any

number of balun type network can be employed so long as

the network presents 100 ohms to each port, resonates 1.9

pF capacitance at each port, and exhibits 180 degree phase

difference between the two ports. The network shown in

Figure 1 combines very well without a lot of added board

space or complexity. Essentially, a quarter wavelength of

transmission line (~1.5 inches of 50 ohms stripline in FR4)

is used with additional phase shift coming from capacitors

C12, C13 and C16. This network will operate anywhere from

800–1000 MHz by adjusting bias inductor L4 and C16 only.

The exciter input requires external matching and a DC

block. It is best matched to 50 ohms using a short 50 ohms

transmission line followed by a 5–10 pF shunt capacitor. The

exciter output is approximately 50 ohms resistive in parallel

with 4 pF of capacitance in the 800–1000 MHz range. It is

best matched to 50 ohms using a 6–10 nH bias inductor

placed as close to the IC as possible. The exciter is

conditionally stable. Placing a 100-300 ohm resistor in

parallel with the bias inductor, when driving large VSWR

loads, may be needed to keep the exciter stable.

Supply decoupling must be done as close to the IC as

possible. A 1000 pF capacitor is recommended. An

additional 100 pF capacitor and an RF choke are

recommended to keep the LO signal off the supply line.

Enabling/Disabling the MRFIC2101 can be done with the

separate TTL/CMOS compatible enable pins for the mixer

and exciter. The trip point is between 1 and 2 volts.

EVALUATION BOARDS

Evaluation boards are available for RF Monolithic Inte-

grated Circuits by adding a “TF” suffix to the device type.

For a complete list of currently available boards and ones

in development for newly introduced product, please con-

tact your local Motorola Distributor or Sales Office.

MRFIC2101

8

MOTOROLA RF DEVICE DATA

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