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AN3100

更新时间： 2022-04-23 23:00:11

品牌	Logo	应用领域
飞思卡尔 - FREESCALE		放大器
页数	文件大小	规格书
4页	65K
描述
General Purpose Amplifier Biasing

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AN3100 数据手册

AN3100

Rev. 0, 3/2005

Freescale Semiconductor

Application Note

General Purpose Amplifier Biasing

by: Jeff Gengler

Freescale Semiconductor

HBT devices are current-driven; therefore, Freescale

recommends that designers use a constant current source to

minimize the impact of shifts in supply voltage and shifts in the

temperature of the operating environment. Deviations from

the optimal current can impact both power and linearity

performance. A series resistor between the voltage supply

and collectors of the Darlington is the easiest way to emulate

a constant current source (R6 in Fig. 1). This is necessary for

the MMG3001NT1, MMG3002NT1 and MMG3003NT1

devices.

Because the RF output of the Darlington Pair is also used

for the DC bias, an RF choke is required (L1) to connect the

voltage supply to the output. RF coupling capacitors may also

be required on the RF input and RF output because the input

and output of the devices are DC coupled.

INTRODUCTION

Freescale Semiconductor’s General Purpose Amplifier

(GPA) devices are all designed to operate from a single

positive voltage supply. The GPAs have output powers

ranging from 12 to 34 dBm. They are currently designed with

three different circuit techniques:

• Darlington Pair

• Discrete with integrated current mirror

• Field Effect Transistor (FET) operating at zero gate voltage

drain leakage current (I_DSS

)

and use two different device technologies:

• Indium Gallium Phosphide Heterostructure Bipolar

Transistors (InGaP HBT)

Since the release of these first three devices, Freescale has

developed a method to eliminate the need for an external

resistor and to enable the devices to operate directly from a

positive 5 Volt supply. This approach has exceptional current

stability over temperature and has a pending patent. All

Darlington HBT products with the exception of the

MMG3001NT1, MMG3002NT1 and MMG3003NT1 use this

approach (Fig. 2).

• GaAs Heterostructure Field Effect Transistor (HFET)

The required biasing methods for the different circuit

schemes are described in this application note.

GPA CIRCUIT DESIGN METHODS

Freescale’s InGaP HBTs are designed using one of two

different circuit methods. The low power GPAs (P1dB from 12

to 24 dBm) are designed using a Darlington Pair (Fig. 1). The

Darlington Pair is biased when voltage is applied to the

collector of discrete devices Q1 and Q2. Resistor R1 is used

for negative feedback of the amplifier but is also part of the

voltage divider with R2 to establish the base bias on Q1.

SUPPLY

OUTPUT

SUPPLY

INPUT

OUTPUT

INPUT

PACKAGED DEVICE

Figure 2. Improved Darlington Pair InGaP HBT

Bias Scheme

PACKAGED DEVICE

Figure 1. Darlington Pair InGaP HBT Bias Scheme

AN3100

RF Application Information

Freescale Semiconductor

12 3 4

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