Izmir Katip Celebi University: Eee468 Microwave Electronics

Izmir Katip Celebi University
EEE468 MICROWAVE ELECTRONICS
PROJECT TOPIC : PIN Diode

Attenuator
120403034 SERKAN BOZ

What is the meaning of Attenuator?
An attenuator is an electronic device that reduces the power of a signal without
appreciably distorting its waveform.
An attenuator is effectively the opposite of an amplifier, though the two work by different
methods. While an amplifier provides gain, an attenuator provides loss, or gain less than 1.
Construction and usage

Attenuators are usually passive devices made from simple voltage
divider networks. Switching between different resistances forms adjustable stepped
attenuators and continuously adjustable ones using potentiometers. For higher frequencies
precisely matched low VSWR resistance networks are used.
Fixed attenuators in circuits are used to lower voltage, dissipate power, and to
improve impedance matching. In measuring signals, attenuator pads or adapters are used to
lower the amplitude of the signal a known amount to enable measurements, or to protect the
measuring device from signal levels that might damage it. Attenuators are also used to
'match' impedance by lowering apparent SWR.
Attenuator circuits and characteristics
Attenuator circuits
Basic circuits used in attenuators are -type and T pads. These may be required to be balanced or
unbalanced networks depending on whether the line geometry with which they are to be used is balanced
or unbalanced. For instance, attenuators used with coaxial lines would be the unbalanced form while
attenuators for use with twisted pair are required to be the balanced form.
Attenuator characteristics
Key specifications for attenuators are:

Attenuation expressed in decibels of relative power. A 3 dB pad reduces power to one half, 6 dB to one
fourth, 10 dB to one tenth, 20 dB to one hundredth, 30 dB to one thousandth and so on. For voltage you
double the dBs so for example 6 dB is half in voltage.
Nominal impedance, for example 50 ohm
Frequency bandwidth, for example DC-18 GHz
Power dissipation depends on mass and surface area of resistance material as well as possible additional
cooling fins.
SWR is the standing wave ratio for input and output ports
Accuracy
Repeatability
RF attenuators
Radio frequency attenuators are typically coaxial in structure with precision

connectors as ports and coaxial, micro strip or thin-film internal structure.
Above SHF special waveguide structure is required.
Important characteristics are:
accuracy,
low SWR,
flat frequency-response and
repeatability.
The size and shape of the attenuator depends on its ability to dissipate power.
RF attenuators are used as loads for and as known attenuation and protective
dissipation of power in measuring RF signals.[2]
PIN Diode Attenuator
PIN diode-based Automatic Gain Control (AGC) attenuators

are commonly used in many broadband system applications
such as cable or fiberoptic TV, wireless CDMA, etc. A
popular attenuator design used over the instantaneous
frequency range from 10 MHz to beyond 2 GHz is the PI
network. The benefit of this design is its broadband
constant impedance, wide dynamic range, and good
compatibility with AGC signals.
The PIN diode is used as a current-controlled resistance
component in the PI network. PIN diodes are low-cost,
lowdistortion elements available in commonly used small
plastic packages
PIN diode variable RF attenuator circuit
is a constant impedance circuit design for variable voltage controlled

attenuators using PIN diodes for use in a variety of RF design applications
including programmable RF attenuators.
Voltage controlled RF attenuators are often used in RF designs. For example,
it is often necessary to be able to control the level of a radio frequency signal
using a control voltage. These variable RF attenuators can even be used in
programmable RF attenuators. Here the known voltage generated by a
computer for example can be applied to the circuit and in this way create a
programmable RF attenuator.
Often when designing or using variable or programmable RF attenuators, it is
necessary to ensure that the RF attenuator retains a constant impedance over
its operating range to ensure the correct operation of the interfacing
circuitry. This RF attenuator circuit shown below provides a good match to 50
ohms over its operating range.
PIN Diode RF attenuator circuit description
The PIN diode variable attenuator is used to give attenuation over a
range of about 20 dB and can be used in 50 ohm systems. The
inductor L1 along with the capacitors C4 and C5 are included to
prevent signal leakage from D1 to D2 that would impair the
performance of the circuit.
The maximum attenuation is achieved when Vin is at a minimum. At
this point current from the supply V+ turns the diodes D1 and D2 on
effectively shorting the signal to ground. D3 is then reverse biased.
When Vin is increased the diodes D1 and D2 become reverse biased,
and D3 becomes forward biased, allowing the signal to pass through
the circuit.
Typical values for the variable RF attenuator circuit might be: +V :
5 volts; Vin : 0 - 6 volts; D1 to D3 HP5082-3080 PIN diodes; R1 2k2;
R2 : 1k; R3 2k7; L1 is self resonant above the operating frequency,
but sufficient to give isolation between the diodes D1 and D2.
These values are only a starting point for an experimental design,
and are only provided as such. The circuit may not be suitable in all
instances.

Izmir Katip Celebi University: Eee468 Microwave Electronics

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Izmir Katip Celebi University: Eee468 Microwave Electronics

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Izmir Katip Celebi University

EEE468 MICROWAVE ELECTRONICS

PROJECT TOPIC : PIN Diode

120403034 SERKAN BOZ

Construction and usage

Key specifications for attenuators are:

Radio frequency attenuators are typically coaxial in structure with precision

PIN diode-based Automatic Gain Control (AGC) attenuators

is a constant impedance circuit design for variable voltage controlled

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