MRFIC2004 データシートの表示（PDF） - Motorola => Freescale

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MRFIC2004

900 MHz Driver and Ramp

Motorola => Freescale 

APPLICATIONS INFORMATION

DESIGN PHILOSOPHY

The MRFIC2004 was designed as a support IC for a CT2

chip-set. The other chips making up the chip-set are the

MRFIC2001 downconverter, the MRFIC2002 transmit mixer,

the MRFIC2003 antenna switch and the MRFIC2006 PA. A

complete CT2 front-end solution requires a ramp for burst

control, an inverter for complementary antenna switch con-

trol and gain control (or an attenuator) for the transmitter low

power mode. In order to keep the other chips in the chip-set

relatively general purpose, yet provide the system designer

with an easily controlled solution, these functions were com-

bined with a driver amplifier into one IC, the MRFIC2004.

THEORY OF OPERATION

The driver is a cascode design that exits the IC open-

collector. Impedance matching must be done externally.

Since the output requires a bias inductor and DC blocking

capacitor, the output can be matched with these two ele-

ments. To keep the driver unconditionally stable, it is recom-

mended that a 300 – 400 ohm resistor be placed in parallel

with the bias inductor as close to the IC as possible. Since

the output impedance of the driver by itself is very high, the

resistor sets the output impedance. The input can be

matched with a series inductor followed by a shunt capacitor.

Alternatively, a series transmission line followed by a shunt

capacitor can be used. A DC block is also required on the

input.

Gain control is provided to meet the CT2 low power

mode requirement. The CT2 Common Air Interface specifi-

cation requires the transmitter to be capable of dropping

the output power by 16 ± 4.0 dB. Although the driver has

34 dB of small signal gain control, it can be reduced by ad-

ding a resistor in series with the gain control pin. The value

of the resistor depends on the logic levels being used and

the amount of gain compression after the driver. Also, the

amount of gain control is a function of the driver input power

level. The input power should be kept less than –10 dBm to

allow for sufficient gain control to achieve the low power

mode. The gain control can also be used for PA output power

trimming. However, this is not an efficient method.

The ramp is an integrator which is used to slow down the

driver and PA turn-on and turn-off times to reduce AM splat-

ter. By applying a pulse waveform to the input, a linear ramp

waveform is created at the output which is then applied to the

current mirrors of the driver and PA. An external integrating

capacitor is used so that the rise/fall time can be pro-

grammed externally. A minimum value of 2.0 – 2.4 nF is

needed to meet the CT2 Common Air Interface splatter spec-

ification. For non-TDD/TDMA systems the ramp reverts to an

enable/disable function.

The inverter is CMOS/TTL compatible and was included to

provide complementary control for an antenna switch such

as the MRFIC2003. By applying the receiver enable control

line, RXEN, to the inverter the inverse RXEN will be created.

RXEN and RXEN can then be used to control the

MRFIC2003 antenna switch.

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.

MRFIC2004

6

MOTOROLA RF DEVICE DATA

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