Transcript Tjaart Opperman

A 5 GHz Voltage Controlled Oscillator (VCO)
with 360° variable phase outputs
Presented by Tjaart Opperman ( [email protected])
Program: (MEng) Micro-Electronic Engineering (University of Pretoria)
Supervisor: Saurabh Sinha
AGENDA
• Introduction
• Motivation for Design
• Methods of Phase Shifting
• Design Specifications and Goals
• Circuit Realization and Simulation Results
• Circuit Layout
• Integration with Modern Modulation Schemes
• Summary
• Questions/Comments?
Slide 2
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Introduction – What is a VCO?
VoltageControlled
ControlledOscillator
Oscillator(VCO)
(VCO)with 360°
Topic: A 5 GHz Voltage
variable phase outputs
•
Slide 3
Voltage Controlled Oscillator – The frequency of the
output signal is controlled by applying a voltage at a
selected input.
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Introduction – What is meant by
phase-shifting?
Topic: A 5 GHz Voltage Controlled Oscillator (VCO) with 360°
variable
variablephase
phaseoutputs
outputs
•
Slide 4
Phase shifting - When a signal is being delayed for a
certain time causing it to be out of phase by a certain
angle with a reference signal.
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Introduction – How phase shifting is
achieved
• There exists a number of Microwave devices that are used to
obtain phase shifting. These include mostly ferrite phase
shifters and diode phase shifters. MMIC phase shifters and
MEMS phase shifters are also being developed.
A non reciprocal ferrite “latching” phase
shifter.
Two p-i-n diode phase shifters
that are of the loaded line type.
Both these images were obtained from (D. Parker and D.C. Zimmerman, Phased
Arrays-Part II: Implementations, Applications, and Future Trends, IEEE Trans.
Microwave Theory Tech., vol. 50, 2002).
Slide 5
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Introduction – The vector sum method of
phase shifting
VGA
In-phase
+-
Vcontrol_I
+
Vector
Sum
90°
VGA
Quadrature
+-
Vcontrol_Q
• 360° phase shifting is obtained by the vector sum of orthogonal
signals of which the amplitudes are varied.
Slide 6
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Introduction – Typical performance
parameters of various phase shifters
Parameter
Loss (dB)
Rotary field
P-I-N diode
ferrite [1]
[1]
MEMS [1]
MMIC [1] [2]
Analogue IC
[3] [4] [5]
0.7
1.4~2.3
1
8
N/A
25×66
15×28
2×2
1×0.8
1×1
Mass (kg)
1.3
0.270
0.003
0.003
0.003
Power Handling (W)
120
2
1
0.5
0.4~1
High
Moderate
High
Moderate
Low
Size (mm2)
Cost
This work
[1] Parker et al.
[2] P.-S. Wu et al., New Miniature 15-20-GHz Continuous-Phase/Amplitude Control MMICs Using
0.18-um CMOS Technology, IEEE Trans. Microwave Theory Tech., vol. 54, 2006.
[3] X. Guan et al., A Fully Integrated 24-GHz Eight-Element Phased-Array Receiver in Silicon,
IEEE J. Solid-State Circuits, vol. 39, 2004.
[4] Gueorguiev et al., A CMOS transmitter for 802.11a WLAN with beam forming capability,
Circuits and Systems 2005.
[5] This work.
Slide 7
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Motivation for Design - Antenna Arrays
•
Single-element linear antennas tend to spread radiated
power over the broad beams in their radiation patterns.
An array of antenna elements can be used to control the
directionality of the radiation pattern.
This architecture is mostly applied to RADAR systems and
could be beneficial towards communications systems as
well (e.g. smart antennas).
•
•
A giant phased-array RADAR in Alaska, USA 
Slide 8
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Motivation for Design - Antenna Arrays
•
Slide 9
This beam formation
capability of antenna
arrays is achieved by
tuning the phase and
amplitude of the
transmitting signal,
individually for each
antenna element. (Note
that no mechanical
movement is required!)
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A beam-forming back end and corresponding
antenna pattern (Gueorguiev et al., A CMOS
transmitter for 802.11a WLAN with beam
forming capability, Circuits and Systems 2005)
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Design Specifications and Goals (2007)
1. To design a quadrature VCO with a tuning range of
4.6 to 5.3 GHz.
2. The VCO must have multiple outputs and the phase shift of
each output must be independently variable over its entire
cycle (i.e. 360°).
3. The phase shifting must be accomplished using the vector
sum method.
4. The entire design must be implemented on an Integrated
Circuit (IC) using the AMS S35 SiGe BiCMOS process.
Slide 10
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Design Specifications and Goals (2008)
5. The design must be fabricated through Europractice (which
is also a requirement for the Master’s degree:
Micro-Electronic Engineering, University of Pretoria).
6. Measurements on the actual product must be performed
and compared to predicted values. This includes critical
performance indicators such as
•
•
•
•
•
Slide 11
phase noise,
phase error,
power consumption,
yield and
temperature sensitivity.
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An example of an
IC-package (left).
The image was
obtained from
(www.onsig.com).
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Circuit Realization – Design spec. 1: VCO
3.3V
On-chip spiral
inductors
270°
180°
Vtune
Vtune
90°
0°
270°
0°
90°
180°
ICoupling
IBias
Coupling transistors
• On-chip spiral inductors are used in the LC-tank.
• The quadrature signals are obtained by coupling two VCOs
•
Slide 12
together.
The coupled oscillators synchronize to exactly the same
frequency, in spite of mismatches in their resonant circuits.
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Simulation Results – Design spec. 1: VCO
(GHz)
Output
OutputFrequency
Frequency (Hz)
5.4
x 10
Tuning characteristic of the VCO
9
5.2
5
4.8
4.6
4.4
4.2
0
0.5
1
1.5
2
2.5
3
Vtune (V)
• Simulation results show that this design specification has been
achieved.
Slide 13
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Circuit Realization – Design spec. 2 and 3:
Phase shifter
VGA
Isum-
In-phase
Isum+
+-
Vcontrol_I
Gilbert
Mixer
90°
VGA
+
Vector
Sum
Vosc+
Vcontrol-
Quadrature
Gilbert
Vcontrol_Q
Mixer
The schematic of the Gilbert Mixer used for a Variable Gain Amplifier
(VGA).
The current of the mixers are combined to obtain the vector sum.
The differential architecture of the Mixer requires the transistors used
as current sources to be closely matched.
+-
•
•
•
Vcontrol+
Vosc-
Slide 14
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Simulation Results – Design spec. 2 and 3:
Phase shifter
• The quadrature amplitude was held constant while the in-phase
•
Slide 15
voltage amplitude was swept.
The phase shift was then measured.
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Simulation Results – Design spec. 2 and 3:
Phase shifter
• Since the quadrature amplitude was held constant, the vector
sum amplitude decreased by a factor of 2.
Slide 16
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Circuit Layout
A cross section of the
AMS S35 SiGe BiCMOS
process wafer. This image
was obtained from
(AustriaMicroSystems,
0.35μm HBT BiCMOS
Process Parameters,
ENG-219, Rev. 4.0)
Slide 17
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Circuit Layout
Key features of the AMS S35 process:
• Triple poly, triple metal process + 1 thick metal layer
• SiGe BiCMOS Mixed Signal and RF transistors
• Poly-Poly and Metal-Metal capacitors
• Feature sizes: 0.35 μm gates and 0.4 μm emitters
• Supply voltage 3.3V / 5.5V
• ft > 60 GHz and fmax > 70 GHz
• BVceo > 2V
• 2007 Prototyping cost through Europractice: 1000 EURO/mm2
•
Slide 18
Minimum required size for prototyping: 5 mm2
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Circuit Layout
• The physical layout of the VCO
(right) and the Gilbert Mixer
(below). The complete design
is to be fabricated in 2008.
Slide 19
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Integration with Modern Modulation Systems
•
•
•
The vector sum method creates a variable phase offset on
the harmonic signal it has produced.
The vector sum method therefore does not shift the phase
of an incoming signal as with conventional phase shifters.
The most straight forward application for this kind of
phase shifter would be to transmit information using
Frequency-Shift Keying (FSK).
Data
Frequency
control
90°
Slide 20
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Phase
shifter 1
PA1
Phase
shifter 2
PA2
Phase
shifter n
PAn
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Integration with Modern Modulation Systems
•
•
•
Take note of the added advantage that the FSK design provides,
that is: Integrating a single high-output power amplifier (PA)
for one antenna is less favorable than integrating a number
of lower-output PAs, with an equivalent output power in
total. (Gueorguiev et al.)
We need to be able to apply this technology to various other
modulation methods as well.
One solution would be to apply the phase shift to the local
oscillator (LO), as shown below.
IF signal
Frequency
control
90°
Slide 21
Phase
shifter 1
LO1
×
PA1
Phase
shifter 2
LO2
×
PA2
Phase
shifter n
LOn
×
PAn
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This architecture
can be applied to
the receiver side
as well.
•
Summary
Beam-forming allows the transmitter to transmit less power to
cover the same distance and this is achieved with the aid of
phase shifters.
•
Although the Analogue IC vector sum phase shifter has much
lower power handling capability than most microwave phase
shifters, it is much smaller, cheaper (when mass produced)
and can adapt very quickly.
•
Such an IC has been designed and simulated operating at
5 GHz. It is worth investigating the application of this
technology for a low cost, portable C-band RADAR (the CSIR
and the DoD could benefit from this).
•
Instead of having to integrate a single high-output PA for only
one antenna, with phased-arrays it is possible to integrate
multiple lower-output PAs.
Slide 22
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Questions/Comments?
Slide 23
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