Transcript Microwave Integrated Circuits (MIC)

Microwave Integrated Circuits (MIC)
Microwave circuits exist in three different forms:
Discrete circuit
Packaged diodes/transistors mounted in coaxial and waveguide
assemblies. Devices can usually be removed from the assembly and
replaced
Hybrid MIC
Diodes/transistors, resonators, capacitors, circulators, … are
fabricated separately on most appropriate material and then
mounted into the microstrip circuit and connected with bond wires
MMIC
Diodes/transistors, resistors, capacitors, microstrip,…all fabricated
simultaneously, including their interconnections, in semiconductor
chip
Advantages and Disadvantages of HMIC
Advantages:
1- Each component can be designed for optimal performance:
 Each transistor can be made of the best material.
 Other devices can be made of the most
appropriate
material.
 The lowest loss microwave components can be made by
choosing the optimal microstrip substrate.
2- It has high power capability since the high power generating
elements can be optimally heat-sinked
3- Standard diodes and transistors can be used and made to
perform different functions by using different circuit
design.
4- Special-purpose devices for each function are not required.
5- Trimming adjustments are possible
6- The most economical approach when small quantities, up
to several hundred, of the circuits are required.
Disadvantages:
1- Wire bonds cause reliability problems. Each circuit
element that is not part of the microstrip assembly must be
attached to the microstrip by a wire bond.
2- The number of devices that can be included is limited by
the economics of mounting the devices onto the circuit and
attaching them by a wire bonds. The circuit is usually
limited to a few dozen compartments.
Advantages and Disadvantages of MMICs
Advantages:
1- Minimal mismatches and minimal signal delay
2- There are no wire bond reliability problems
3- Up to thousands of devices can be fabricated at one time
into a single MMIC.
4- It is the least expensive approach when large quantities are
to be fabricated.
Disadvantages:
1- Performance compromised, since the optimal materials
cannot be used for each circuit element.
2- Power capability is lower because good heat transfer
materials cannot be used
3- Trimming adjustments are difficult or impossible.
4- Unfavorable device-to-chip area ratio in the
semiconductor material.
5- Tooling is prohibitively expensive for small quantities of
MMIC.
Materials used for MIC
The basic materials for fabricating MICs, in general are
divided into four categories:
1- Substrate materials sapphire, alumina, ferrite/garnet,
silicon, RT/duroid, quartz, GaAs, Inp, etc.,
2- Conductor materials-copper, gold, silver, aluminum, etc.
3- Dielectric films SiO, SiO2,…etc
4- Resistive films- Nichrome (cNiCr), tantalum (Ta)
Substrate Materials:
1- The cost of the substrate must be justifiable for the application
2. Is the technology to be thin- or thick film?
3- The choice of thickness and permittivity determines the
achievable impedance range and the usable frequency range.
4- There should be low loss tangent for negligible dielectric loss
5- The substrate surface finish should be good (~ 0.1 mm), with
relative freedom from voids, to keep conductor loss low and yet
maintain good metal-film adhesion
6- There should be good mechanical strength and thermal
conductivity.
7- No deformation should be occur during processing of circuit
8- A substrates with sufficient size are for the particular application
and complexity should be available
Conductor Materials:
High conductivity, low temperature coefficient of
resistance, low RF resistance, good adhesion, good etchability and solder-ability, and be easy to deposit.
Dielectric Material:
Used as insulators for capacitors, protective layer for active
devices, and insulating layer for passive circuits.
The desirable properties:
Reproducibility, high breakdown voltage, low loss tangent,
and the ability to under go processing without developing
pin holes
Resistive Films:
Required for fabricating resistors for terminations, attenuators,
and for bias networks.
The properties required for resistive material are: Good
stability, low temperature coefficient of resistively
Sheet sensitivities in the range of 10 to 2000 W/square
1% accuracy is achievable
The creation of these resistive films demands additional
processes of deposition and etching beyond those of the thinfilm metallization. This complexity may be obviated by
bonding directly chip resistors onto the conducting pattern (ex.
using surface mount).
Planar and Uniplanar Transmission lines
Microstrip TL
Slot line
Coplanar Wave-Guide (CPW)
Material
er
Tan d
Ther. Cond. Tmax during Fab.
W/inoC
(Co)
Teflon-
2.5
10×10-4
0.007
200
Epsilam 10
10
15×10-4
0.01
150
Alumina
10
1×10-4
0.1
500
Beryllia
6
2×10-4
1
500
Ferrite
15
2×10-4
0.1
500
Silicon
12
30×10-4
0.4
400
GaAs
12
16×10-4
0.1
400
fiberglass
Microstrip Circuit elements commonly used in HMIC
The components that can be fabricated as part of the
microstrip transmission line are:
Matching stubs and transformers
Directional couplers
Combiners and dividers
Resonators
Filters
Inductors and capacitors
Thin film resistors
Coupled line filter
Hybrid coupler
Branch line coupler
Microstrip coupler
Typical spiral inductor and interdigitated capacitor
Loop inductor
High impedance transmission line inductor
Figure: Microstrip elements used in HMIC
Components Added After Microstrip Fabrication
The MIC Components that are fabricated separately and
added to the microstrip circuits are:
Bond wire
Chip resistor
Chip capacitors
Dielectric resonators
Circulators
Diodes and transistors
Bond wires
Dielectric resonator
Chip capacitor and resistor
Passive Microwave Components (PMC)
(The circuits that does not contain any active device such as diode
or transistor)
PMC are used extensively in any microwave communication
system
Passive microwave components include:
• Terminations &
attenuators
• Switches
• Couplers
• Isolators & Circulators
• Combiners & Dividers
• Phase shifters
• Filters
Terminations
Absorb all the power at the end of transmission line in order to
terminate a microwave equipment without allowing the power to
escape into surroundings or to be reflected back into the
equipment.
Termination can be found in the form of:
 Waveguide,
 Coaxial line
 Microstrip
In waveguide form it contains a tapered absorber, usually
consisting of a carbon-impregnated dielectric material that
absorbs the microwave power
Some Types of Terminations
8.2 – 12.4 GHz
handles 75 watts
GHz7 - 10
watt300
Important specifications:
 SWR (or S11)
 Power-handling capability
Coaxial terminations
50 W N-type
50 W SMA
75 W BNC
Strip Line Load
100 W
High power 50 W)
GHzDC- 3
Cwwat600 Type C
Attenuators
Used to adjust the power level of microwave signals.
Attenuators Types:
 Fixed (Pads)
 Mechanically adjustable
 Electronically Controlled
Coaxial attenuators cover the frequency range from dc to
18 GHz, and they can have any value of attenuation.
Typical values are 3, 6 10, and 20 dB.
Coaxial Attenuators
3 dB 1 W DC- 2 GHz
N-Type
Fixed coaxial attenuator
The lossy material extending from
the center to the outer conductor and
along the center conductor. This
lossy material forms a resistive T,
which absorbs some of the
microwave power without reflecting
any type
30 dB 100 W DC- 21GHz
N-Type QC
Mechanical variable attenuator
8.2 – 12.4 GHz 0 - 20 dB
A van of absorbing material inserted
into the waveguide through a slot on
the broad wall. The greater the
penetration of the vane the greater
the attenuation. The dial can be
calibrated in dB
12.4 – 18 GHz 0 - 50 dB
Electronically variable attenuator
Achieved with PIN diodes
Will be covered in active circuits
Switches
Direct s microwave power from one transmission line to another
or turns microwave power on and off. Switches can be
mechanically or electronically. Here we discuss some types of
mechanical switchs. Electronically switches will be introduced
in active devices section.
Directional Couplers
Directional couplers sample the power traveling in only one
direction down a transmission line.
Pc
Pwrong
Pi
Po
Important specifications:
 Coupling Factor (dB) C = 10 log Pi/Pc
How much of the input power is sampled
 Insertion Loss IL = 10 log Pi/Po
Specify the output power relative to the input
power
 Directivity D = 10 log Pc/Pwrong
No coupler is perfect i.e Pwrong  0
 Isolation
I = 10 log Pi/Pwrong
=
D + C dB
The amount of power sampled in the wrong direction
Typical values are 3, 6, 10, 20, 30, 40, and 50 dB
Directional coupler can also be used as an attenuator
and to measure the reflected power from a mismatch
lg/4
Coupled
power
Input
power
Output
power
Coupling Loss vs Coupling Factor
Directional Coupler Signal Paths
Wave guide coupler
Coaxial and microstrip coupler
High power
Wide band
High directivity
Poor directivity
limited in BW
Limited power
Waveguid coupler
D is not critical for sampling
microwave power
D is extremely important for a
return loss measurement, to
measure the small power
reflected from the mismatch.
Coaxial coupler
Microstrip coupler
3-dB Quadrature Hybrid (Hybrid Coupler)
(Input) 1
l/4
2
(output)
l/4
(Isolated)
4
3 (output)
The 3-dB quadrature hybrids are used as components, in almost every RF
System, such as:
 Power combiners and dividers
 Balanced Mixers
 Balanced amplifiers
De(modulators)
 Image rejection mixers
 Feed network in antenna arrays
With all ports matched, power entering port 1 is divided between ports 2 and 3,
with 90o phase shift between these outputs. No power is coupled to port 4. Ports 1
and 4 as well as ports 2 and 3 are isolated.
The most important parameters of the hybrid are
Isolation between isolated ports
SWR at the input ports
Phase difference between the two coupled ports
Insertion loss between the input and the coupled ports
The [S] matrix is
-1
[S] =
2
0
j
1
0
j
0
0
1
1
0
0
j
0
1
j
0
Small size coupler
(2) 180o Hybrid Ring:
The 0o/180o hybrid coupler is preferred in some applications,
namely,
 Mixers
 Modulators
 Isolated power splitters since the isolation between its
input ports may be independent of
the value of the two
balanced impedance loads.
3
1
lg/4
4
2
3lg/4
The [S] matrix is
-j
[S] =
2
0
1
1
0
1
0
0
-1
1
0
0
1
0
-1
1
0
Some Small size couplers configurations
Combiners and Dividers
Combiners are used to combine two or more transmission
lines into one transmission line. They can also be used to
divide the microwave signal from one transmission line into
two transmission lines
The T- Junction Power Dividers (simplest configuration)
E-plane waveguide T
Microstrip T-junction
H-plane waveguide T
 Lossless junctions
 Can not be matched simultaneously at all ports
 No isolation between the two input lines
Resistive Divider
Matching T-junctions is possible if a lossy components
is inserted in series to all branches at the junction
Dissipate half of the supplied power and the two output
ports may not be isolated
Wlikinson Power divider
Wilkinson power divider, is a wide band circuit (2:1 or more),
can be matched at all ports and lossless when the output ports are
matched. It can also be designed to give arbitrary power division.
This divider is often made in microstrip or stripline form.
In-phase Wilkinson divider
Isolation is achieved between ports by terminating resistors. Any
unequal mismatch or out-of-phase condition that would couple
power from one line to the other is attenuated by the resistor.
Disadvantages:
The termination must be mounted inside the coupler, which limits
its power handling capability
Multi-channel Combiner
Lossy
Very little selectivity
Small size
Wide band
Magic-T
The 180o hybrid can also be implemented in waveguide
form as shown in the Figure. The waveguide magic-T
hybrid junction has terminal properties similar to those of
the ring hybrid. In practice, tuning posts irises are often
4
used for matching.
3
2
1
The Lange coupler
Tight coupling 3 or 6 dB
Wide band (as high as 4:1)
It is a type of quadrature coupler (90o phase
shift between 2 and 3)
Lines are very narrow
Bonding wires are needed
4
2
l/4
1
3
Phase Shifters
Microwave signals are characterized by amplitude and
phase. The amplitude is controlled with amplifiers and
attenuators. The phase can be controlled by phase shifters.
Phase shifters like attenuators, can be mechanically or
electronically adjustable
Mechanically adjustable phase shifters
It is a line stretchers. The phase shift can be adjusted by
changing the signal path.
Isolators and Circulators
[S] =
0 0
1 0
An isolator allows microwaves to pass in one direction but
not the other, so it has unidirectional transmission
characteristics. This isolating effect is achieved with
ferrites
Isolators are usually used to protect high power microwave
sources from possible reflection that may cause source
damage. It can also be used in place of matching networks.
The most important specifications for isolators are the
isolation which is the insertion loss in the reverse direction
and the forward insertion loss. The isolation should be high
and the insertion loss should be low. Typical values are 20
dB for isolation and 0.5 dB for insertion loss.
•Purpose of Isolator
Low insertion loss in the normal or forward path
High isolation in the reverse path
•Uses
Circulators providing input and output isolation for a one port amplifier
Isolator minimizing the pulling effect of an oscillator
Isolator reducing the power reflected back to a mixer
Reduce VSWR interactions between RF components
Isolators are not a broadband as attenuators
Circulator
Circulator route microwave signals from one port of the device to another. For
example, a microwave signal entering port 1 is directed out of the circulator at port
2. A signal entering port 2 is routed to leave the circulator at port 3 and does not get
back into port 1. A signal entering port 3 does not get into port 2, but goes out
through port 1. The S matrix of an ideal circulator is
3
0 0 1
[S] =
1 0 0
0 1 0
2
1
The important specifications of a circulator are the insertion loss,
which is the loss of signal as it travels in the direction that it is
supposed to go, and the directivity, which is the loss in the signal as
it travel in the wrong direction. Insertion loss is typically 0.5 dB and
the directivity is 20 dB. Circulator enable the use of one antenna for
both transmitter and receiver of communication system.