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INA-12063

1.5 GHz Low Noise Self-Biased Transistor Amplifier

HP => Agilent Technologies 

INA-12063 Applications

Information

Introduction

The INA-12063 is a unique RFIC

configuration that combines the

performance flexibility of a

discrete transistor with the

simplicity of using an integrated

circuit.

The INA-12063 is an integrated

circuit that combines three

functions: (1) a silicon bipolar RF

transistor, (2) an RF feedback

network, and (3) a patented[1]

bias regulation circuit. A simpli-

fied schematic diagram of the

INA-12063 is shown in Figure 9.

The result is a versatile gain stage

that can be operated from a single

+1.5 to +5 volt power supply with

the device current set by the user.

The INA-12063 is designed for use

in battery powered equipment

demanding high performance

with low supply voltages and

minimal current drain. Typical

applications for the INA-12063

include low noise RF amplifiers,

IF amplifiers, gain and buffer

stages through 2 GHz. The

INA-12063 is an excellent choice

for use in cellular and cordless

telephones, PCS, W/LAN’s, RF

modems and other commercial

wireless equipment.

GND 2

RF

INPUT

Vd

ACTIVE

BIAS

CIRCUIT

RF

TRANSISTOR

RF

FEEDBACK

NETWORK

GND 1

Ibias

RF

OUTPUT

and Vc

Figure 9. INA-12063 Schematic.

Description

The active bias circuit solves

three problems normally encoun-

tered with traditional approaches

for biasing discrete transistors.

First, as an active bias circuit, the

emitter of the RF transistor is DC

grounded. This permits the

collector current to be controlled

without the need for resistors

and/or bypass capacitors in the

emitter that may degrade RF

performance.

Second, the internal bias circuit

greatly simplifies the design tasks

commonly associated with bias-

ing transistors, such as accurately

regulating the collector current,

allowing for variations in hFE,

making a non-intrusive DC

connection to the base of the

transistor, and stabilizing current

over temperature.

And, third, the integrated bias

circuit eliminates the cost, parts

count, and associated PCB space

required for as many as 8 addi-

tional DC components.

The integrated bias control circuit

is very easy to use. For most

applications, the collector current

for the RF transistor can be set

with a single resistor.

The geometry of the integrated

RF transistor is designed to

provide an excellent balance

between low noise figure, high

gain, and good dynamic range

while retaining practical imped-

ance matching levels. The operat-

ing current is typically in the 1 to

10 mA range.

The integrated RF feedback

contains an inductive element in

the emitter circuit of the RF

transistor. This series feedback

configuration is of the type often

implemented in discrete transis-

tor designs for the purpose of

improving stability and bringing

the optimum noise match at the

input of the transistor closer to

50␣ Ω. The result is that for many

applications, a simple, series

inductor is often all that is needed

to adequately match the input of

the INA-12063 to 50 Ω.

In contrast to amplifiers that use

resistive feedback to achieve

broadband 50 Ω input and output

matches, the INA-12063 leaves

the designer with the flexibility of

optimizing performance for a

particular frequency band. For

example, frequency selective

input and output impedance

matching circuits can be used to

tune for optimum NF, maximum

output power, low input VSWR,

or to tailor the passband response

to eliminate undesirable gain

responses.

Setting the Bias Current

The integrated, active bias circuit

is a 10:1 current mirror. The

current mirror forces the collec-

tor current in the RF transistor to

be approximately 10 times the

current supplied to the Ibias pin.

In normal use, a voltage between

+1.5 and +5 volts, is applied to

both the Vd and Vc terminals of

the INA-12063. Although normally

connected to the same supply

voltage, it is not necessary that

both Vd and Vc be at the same

voltage.

The collector current of the RF

transistor is then set by injecting

a small control current into the

Ibias pin that is approximately

1/10 of the desired collector

current.

1 U.S. Patent Number 5436595

6-123

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