PCS LNA/Downconverter

1800-2000 MHz

MADCSM0012

M/A-COM Inc. and its affiliates reserve the right to make changes to the

product(s) or information contained herein without notice. M/A-COM makes

no warranty, representation or guarantee regarding the suitability of its

products for any particular purpose, nor does M/A-COM assume any liability

whatsoever arising out of the use or application of any product(s) or

information.

• North America Tel: 800.366.2266 / Fax: 978.366.2266

• Europe Tel: 44.1908.574.200 / Fax: 44.1908.574.300

• Asia/Pacific Tel: 81.44.844.8296 / Fax: 81.44.844.8298

Visit www.macom.com for additional data sheets and product information.

V2

3

Operating Instructions

Recommended PCB Configuration

M/A-COM’s MADCSM0012 is a highly integrated

MMIC LNA/downconverter for operation in the

1800-2000 MHz PCS frequency band.

The

downconverter

provides

exceptional

RF

performance while consuming low DC current and

is packaged in a low cost plastic package. It is ideal

for lightweight battery operated portable radio

systems.

The MADCSM0012 consists of an LNA, RFA,

single-ended mixer and single-ended IF output

buffer as shown in the block diagram. Surface

mount resistors, inductors and capacitors are used

in conjunction with the LNA/downconverter to

optimize the trade-offs among

performance,

tunability and ease of use.

The sample board

schematic shows the LNA/downconverter and

required off-chip components.

The input of the LNA is matched externally with a

series inductor (L1) and a shunt capacitor (C1) to

provide a low loss match to the optimum noise

impedance in the band of interest.

A high Q

inductor such as Coilcraft’s 0402CS series must be

used if the specified noise figures are to be

achieved.

The series capacitor, C2, is a DC

blocking and input matching capacitor. The LNA is

nominally biased with 15 mA to give an input IP3 of

+6 dBm. An external resistor, R1, may be used to

increase the LNA bias current and thus increase

the IP3. An external image reject filter is required

between the LNA output and RFA input to

prevent downconversion of noise at the image

frequency to the IF. This filter should have a 50-

ohm input and output impedance.

The mixer is a single-ended floating FET mixer that

provides exceptional linearity and isolation with low

loss and no DC current. An off-chip inductor, L3, is

required to match the output of the mixer to the

input of the IF buffer amplifier. The case size of L3

is typically 0603 but if more gain is needed, use a

0805 case size.

The LO input port is matched on-chip to 50 ohms.

An LO buffer amplifier amplifies the -10 dBm input

signal to the level required to drive the mixer.

Performance is optimum with a drive level of -7

dBm.

All DC supply lines must be properly bypassed at

RF frequencies to obtain optimum performance

and at lower frequency to maintain unconditional

stability. Capacitors C4, C5, C6, C7 and C9 are

RF bypass capacitors for the LNA, RFA and LOA.

The value and placement of these capacitors is

critical in determining the frequency response of

these amplifiers. Capacitor C3 is a source bypass

capacitor for the second stage of the low noise

amplifier.

The placement of this capacitor will

affect the gain of the LNA. For best performance,

all the RF bypass capacitors should be placed as

close to the device as possible.

The IF output port is the open drain of the IF buffer

amplifier. This allows maximum flexibility of the

intermediate frequency and also IF filter.

A

matching network such as that shown herein can

be used to match to 50 ohms from the output

impedance of the buffer to the input impedance of

the filter at the 210 MHz intermediate frequency.

The inductor also acts as a choke for the DC

supply line.

Elements L2 and C8 provide the

necessary impedance transformation.