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SW-212 PDF预览

SW-212

更新时间: 2024-09-21 12:20:39
品牌 Logo 应用领域
泰科 - TE 开关射频微波驱动衰减器
页数 文件大小 规格书
4页 87K
描述
Drivers for GaAs FET Switches and Digital Attenuators

SW-212 技术参数

生命周期:TransferredReach Compliance Code:unknown
风险等级:5.19特性阻抗:50 Ω
构造:COMPONENT最大插入损耗:1 dB
最大工作频率:3000 MHz最小工作频率:
最高工作温度:85 °C最低工作温度:-55 °C
射频/微波设备类型:SPST最大电压驻波比:1.8
Base Number Matches:1

SW-212 数据手册

 浏览型号SW-212的Datasheet PDF文件第2页浏览型号SW-212的Datasheet PDF文件第3页浏览型号SW-212的Datasheet PDF文件第4页 
Application Note  
S2079  
Drivers for GaAs FET Switches and Digital Attenuators  
Rev. V5  
Figure 2 shows a 3-bit digital attenuator. Applying the  
correct bias voltage and its complement to any stage  
switches the pad for that stage into the RF signal path.  
Introduction  
Many of M/A-COM's GaAs FET switches and digital  
attenuators cannot operate directly with simple TTL or  
CMOS logic, but instead require external circuits to  
provide appropriate control voltages. This application  
note, an update of M539, Drivers for GaAs FET MMIC  
Switches and Digital Attenuators, provides information  
on M/A-COM's SW-109 and SWD-119 drivers and  
other commercially available digital logic IC's for control  
of switches and digital attenuators.  
GaAs FET’s  
GaAs MMIC control devices such as switches and  
digital attenuators typically employ Field Effect  
Transistors (FET’s). The most common FET is the n-  
channel depletion mode device, which has low source-  
to-drain resistance in the absence of a gate bias, and  
allows a current IDSS to flow. With the application of a  
negative gate bias voltage, the electric field below the  
gate causes the conduction channel to narrow,  
increasing the source-to-drain resistance. The gate  
voltage that creates a high enough resistance to reduce  
the source-to-drain current to (typically) 1 - 2 percent of  
IDSS is known as the pinch-off voltage. For M/A-COM  
FET’s,. the pinch-off voltage is typically –2.5 volts. If  
the transistor is biased at the extremes, (0 V and –5 V  
typically), on and off switching results, providing the  
basis for both GaAs MMIC switches and digital  
attenuators.  
Dual Control Switch Truth Table  
Control A Control B RF Common  
to RF1  
RF Common  
to RF2  
-5 V  
0 V  
0 V  
On  
Off  
Off  
On  
-5 V  
Typical complementary logic control voltages:  
Logic low  
Logic high  
0 V to –2 V @ 20 μA max.  
-5 V to 40 μA typ. To –8 V @ 200 μ  
A max.  
Switch Circuit Topology  
In switches, FET's are arranged in both series and  
shunt configurations. The series FET's provide a  
through-path for the on state, while the shunt FET's  
provide isolation for the off state. The operation of the  
switch requires that series FET's and shunt FET's  
associated with each switch state have opposite (or  
complementary) conduction states and therefore  
Figure 1: Typical Dual Control Switch (SW-239, etc)  
opposite (or complementary) gate biases.  
For  
example, Figure 1 illustrates the operation of a typical  
dual control SPST GaAs MMIC switch. If the RF to  
RF1 path is on and the RF to RF2 path is off, then  
FET's Q2 and Q4 are biased on, while Q1 and Q3 are  
biased off.  
Figure 2: Digital Attenuator Based on Switched Pads  
(AT-230)  
Digital attenuators use series/shunt stages with circuit  
components that form fixed attenuator pads,  
corresponding to digital attenuation bits, switched in or  
out of the transmission path, either individually or in  
combination. Switches require complementary bias  
voltages for each state, while digital attenuators require  
complementary bias voltage to activate each bit.  
1
North America Tel: 800.366.2266 Europe Tel: +353.21.244.6400  
Visit www.macomtech.com for additional data sheets and product information.  
India Tel: +91.80.4155721  
China Tel: +86.21.2407.1588  
M/A-COM Technology Solutions Inc. and its affiliates reserve the right to make  
changes to the product(s) or information contained herein without notice.  

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