ABA-52563 - Agilent / Hewlett-Packard

Agilent ABA-52563

3.5 GHz Broadband Silicon

RFIC Amplifier

Application Note 1349

Introduction

Agilent Technologies’ ABA-52563

is a low current silicon gain block

RFIC amplifier housed in a 6 lead

SC-70 (SOT-363) surface mount

plastic package. Providing a

nominal gain of 21.3 dB and

P1dB of 9.7 dBm at 2 GHz, this

device is ideal for small signal

gain stage or IF amplification.

Distinguished features of the

ABA-52563 which are high gain,

good input and output VSWR and

Vcc

GND 3

2Hx

Input

GND 2

GND 1 Outpu

& Vcc

broad bandwidth made this

device useful in various applica-

tions such as Cellular, Cordless,

Special Mobile Radio, PCS, ISM,

Wireless LAN, DBS, TVRO and

TV Tuner Applications.

In addition to the ABA-52563,

Agilent Technologies also offers a

series of ABA devices with a

range of P1dB. The table below is

a quick reference on the perfor-

mance of the series measured at

2 GHz on the board.

Symbol Unit ABA-51563 ABA-52563 ABA-53563

P1dB dBm 1.8 9.7 12.5

OIP3 dBm 11.4 20.1 22.6

Icc mA 18.4 34.9 46.3

Gp dB 21.3 21.3 21.3

NF dB 3.6 3.6 3.6

VSWR in <1.2 <1.2 <1.2

VSWR out <1.4 <1.4 <1.4

Figure 1. Typical Application Circuit.

RF Outpu

RF Input Vcc

RFC

block

bypass

2Hx

Application Guidelines

The ABA-52563 is designed

with a two stage cascade

consisting in general of a single

input transistor driving a

Darlington connected output

pair. Resistive feedback is used

to set the RF performance. The

collector of the first stage

directly drives the base of the

output stage without any inter-

stage blocking capacitor that

would limit the low frequency

response. The second stages is

fed back using both series and

shunt resistors, sets the match,

gain and flatness of the RFIC.

The Agilent’s HP25 silicon

bipolar process with a cut off

frequency, fT of 25 GHz results

in a device with low current

draw and useful operation up to

3.5 GHz. The ABA-52563 is very

easy to use. For most applica-

tions, all that is required to

operate the device is to apply a

voltage to Pin 4 (Vcc) and Pin 6

(Output and Vcc). All bias

regulation circuitry is integrated

into the RFIC.

RF Input and Output

The RF Input and Output ports of

the ABA-52563 are closely

matched to 50Ω.

DC Bias

The ABA-52563 is a voltage-

biased device that operates at 5V

with nominal current of 35 mA.

Figure 1 shows a typical imple-

mentation of ABA-52563.

The supply voltage for the

ABA-52563 must be applied to

two terminals, the Vcc and the

RF Output pins. The Vcc connec-

tion to the amplifier is RF

bypassed by placing a capacitor

to ground near the Vcc pin of the

amplifier package. The power

supply connection to the RF

Output pin is achieved by means

of a RF choke (inductor). The

reactance of the RF choke must

be relatively higher to 50Ω in

order to prevent loading of the

RF Output. Blocking capacitors

are normally placed in series

with the RF input and RF Output

to isolate the DC voltages on

these pins from circuit adjacent

to the amplifier. The values of the

blocking capacitors are selected

to provide a reactance at the

lowest frequency of operation

that is relatively smaller to 50Ω.

PCB Layout

The ABA-52563 is packaged in

the miniature SOT-363 (SC-70)

surface mount package. A PCB

pad layout for the SOT-363

package is shown in Figure 2.

This layout provides ample

allowance for package placement

by automated assembly equip-

ment without adding pad para-

sitic that could impair the high

frequency performance of the

ABA-52563. The layout is shown

with a nominal SOT-363 package

footprint superimposed on the

PCB pads for reference.

0.026 (0.65)

0.07 (1.75)

0.016 (0.4)

0.035 (0.875)

Figure 2. PCB Pad Layout. Dimensions are in

inches (millimeters).

PCB Materials

Typical choices for PCB material

for low cost wireless applications

are FR-4 or G-10 with a thickness

of 0.025 or 0.032 inches. A

thickness of 0.062 inches is the

maximum that is recommended

for use with this particular

device. The use of a thicker board

material increases the inductance

of the plated through vias used

for RF grounding and may dete-

riorate circuit performance.

Adequate grounding is needed not

only to obtain maximum amplifier

performance but also to reduce

any possibility of instability.

Application Example

An example layout for an ampli-

fier using the ABA-52563 is

shown in Figure 3. This example

uses a microstrip line design

(solid ground plane on the

backside of the circuit board).

The circuit board material is

0.032-inch thick FR-4. Plated

through holes (vias) are used to

bring the ground to the topside

of the circuit where needed.

Multiple vias are used to reduce

the inductance of the path to

ground.

INPUT OUTPUT

ABA-5XX63 DEMO BOARD

Vcc

Figure 3. RF Layout.

Figure 4 shows an assembled

amplifier. The +5 volt supply is

fed directly into the Vcc pin of

the ABA-52563 and into the RF

Output pin through the RF choke

(RFC).

DC blocking capacitors are

required at the input and output

of the IC. The values of blocking

capacitors are determined by the

lowest frequency of operation for

a particular application. The

capacitor’s reactance is chosen

to be 10% or less of the

amplifier’s input or output

impedance at the lowest operat-

ing frequency. For example, an

amplifier to be used in an appli-

cation covering the 1.9 GHz band

would require an input blocking

capacitor of at least 19 pF, which

is 5Ω of reactance at 1.9 GHz.

The Vcc connection to the ampli-

fier must be RF bypassed by

placing a capacitor to ground at

the bias pad of the board. Like the

DC blocking capacitors, the value

of the Vcc bypass capacitor is

determined by the lower operat-

ing frequency for the amplifier.

The reactance of the RF choke

should be large compared to 50Ω,

a typical value for 1.9 GHz

amplifier would be 22 nH.

For this demonstration board,

capacitor C3 provides RF bypass-

ing for both the Vcc pin and the

power supply end of the RFC.

Capacitor C4 is optional and may

be used to add additional bypass-

ing for the Vcc line. A well

bypassed Vcc line is especially

necessary in cascades of ampli-

fier stages to prevent oscillation

that may occur as a result of RF

feedback through the power

supply lines. The value chosen

for the RF choke was 620 nH. All

of the blocking and bypass

capacitors are 1000 pF. These

values provide excellent ampli-

fier performance from 50 MHz

through 2 GHz. Larger values for

the choke and capacitors can be

used to extend the lower end of

the bandwidth. Since the gain of

the ABA-52563 extends down to

Component Value Part number

50 MHz C1, C2, C3 1000 pF Murata GRM40X7R102K50

to RFC 620 nH Coilcraft 1008CS-621XXKBC1

2 GHz C4 (optional) 1 µF

SMA Connectors Johnson 142-0701-881

Table 1. List of Components.

DC, the frequency response of

the amplifier is limited only by

the values of the capacitors and

choke. Table 1 consists of the

components used to assemble the

board. The measurements can be

seen at Figure 5 to Figure 7.

A convenient method for making

RF connection to the demonstra-

tion board is to use a PCB

mounting type of SMA connector

(Johnson 142-0701-881, or

equivalent). These connectors can

be slipped over the edge of the

PCB and the center conductors

soldered to the input and output

lines. The ground pins of the

connectors are soldered to the

ground plane on the backside of

the board. The extra ground pins

for the top of the board are not

needed and can be clipped off.

RF design software such as

Agilent Technologies’ AppCad is

very handy to determine the

values of the blocking capacitors

and RF choke for any operating

frequency. This software is

available at http://

www.agilent.com/view/AppCad

Figure 4. Assembled Amplifier.

INPUT OUTPUT

ABA-5XX63 DEMO BOARD

Vcc

2Hx

RFC

INPUT OUTPUT

2Hx

RFC

Figure 8. Magnified Assembled Board.

FREQUENCY (GHz)

Figure 5. S parameters and Noise Figure vs. Frequency.

S (dB), NF (dB)

-10

-20

-30

-40

-50

1234

S21

S11

S12

S22

FREQUENCY (GHz)

Figure 6. Gain vs. Frequency and Temperature.

GAIN (dB)

1000 2000 3000 4000

-55°C

25°C

125°C

Pin (dBm)

Figure 7. P1dB.

-10

-20

-30

-40 -30 -20 -10 0

Pout (dBm)

P1dB

2 GHz

Notes on RF Grounding

As a direct result of the circuit

topology discussed in the earlier

paragraph, the performance of

ABA-52563 is extremely sensitive

to ground path (“emitter”)

inductance. The two-stage design

potentially creates a feedback

loop being formed through the

ground returns of the stages. If

the path to ground provided by

the external circuit is “long”

(high in impedance) compared to

the path back through the ground

return of the other stage, then

instability can occur.

This phenomena can show up as

a “peaking” in the gain versus

frequency response (perhaps

creating a negative gain slope

amplifier), an increase in input

VSWR or even as return gain (a

reflection coefficient greater

than unit) at the input of the

RFIC.

Evidently, an excellent grounding

is critical when using

ABA-52563. The use of plated

through holes or equivalent

minimal path ground returns

right at the device is essential.

The designs should be done on

the thinnest practical substrate.

The parasitic inductance of a

pair of via passing through

0.032 inches thick PC board is

approximately 0.1 nH, while that

of a pair via holes passing

through 0.062 inches is closer to

0.5 nH. It is recommended that

the PCB trace for the ground

pins NOT be connected together

underneath the body of the

package. PCB pads hidden under

the package cannot be adequately

inspected for SMT solder quality.

These stability effects are en-

tirely predictable. A circuit

simulation using the datasheet

S-parameters and including a

description of the ground path

(via model or equivalent “emit-

ter” inductance) will give an

accurate picture of the perfor-

mance that can be expected.

Device characterizations are

made with the ground leads of

the ABA-52563 directly contact-

ing a solid copper block (system

ground) at a distance of 2 to

4 mils from the body of the

package. Thus the information in

the datasheet is a true descrip-

tion of the performance capabil-

ity of the RFIC, and contains

minimal contributions from the

test fixture.

Phase Reference Planes

The positions of the reference

planes used to measure

S-parameters for this device are

shown in Figure 9. As seen in the

illustration, the reference planes

are located at the point where

the package leads contact the

test circuit.

Figure 9. Phase Reference Plane.

Reference Planes

Test Circuit

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distributors, please go to our web site.

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Data subject to change.

Obsoletes 5988-8966EN

March 25, 2003

5988-9198EN