Datasheet > AN3100

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

The second circuit method is used on the intermediate

power amplifiers (P1dB ranging from 27 to 34 dBm). These

are designed with a MMIC that contains a discrete device, Q1,

with an integrated current mirror to drive the base (Fig. 3).

This active bias approach means that the bias current has

minimal shift with normal supply voltage deviations over the

specified operating temperature range. R6 in Fig. 3 is an

external dropping resistor that is required to establish the

reference voltage on the current mirror that drives the bias of

Q1.

The HFETs are discrete devices that operate directly from

a 5 Volt supply voltage (Fig. 4). The DC blocking capacitor that

is integrated in the feedback loop prevents the gate voltage

from being established with R1 and R2; therefore, the HFET

devices operate at I_DSSwhen 5 Volts are applied to the drain.

L1 is again required as an RF choke as well as the RF coupling

capacitors, C2 and C3.

SUPPLY

OUTPUT

INPUT

ref

PACKAGED DEVICE

OUTPUT

Figure 4. HFET Bias Scheme

INPUT

SUMMARY

The GPA lineup from Freescale is designed to operate from

a single positive voltage supply, which makes them easy to

use. Designers using these devices should be careful to bias

the devices correctly using the appropriate method for the type

of device used. If the current is set too low, linearity and power

will degrade. If the current is set too high, there is some risk

of compromising reliability.

The techniques outlined here are a guide to the bias

approaches for the different technologies and products

available from Freescale. The data sheets for each device

should be followed to achieve optimal performance from all

GPAs.

PACKAGED DEVICE

Figure 3. Intermediate Power InGaP HBT Bias Scheme

The reference voltage (V_ref) is different for each device

based on its size. The data sheets for each device list the

specific reference voltage required for optimal bias current. L1

is required to prevent the DC supply line from improperly

loading the RF output. RF coupling capacitors (C3 and C4 in

Fig. 3) are also required.

The third circuit approach in GPAs is used for the HFET

devices. Bias of this type of device is very similar to the

Darlington circuit technology.

AN3100

RF Application Information

Freescale Semiconductor

123 4

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