Rick Campbell Designer Portland State Universityweb.cecs.pdx.edu/~campbell/CompassRLC.pdf · Rick...
Transcript of Rick Campbell Designer Portland State Universityweb.cecs.pdx.edu/~campbell/CompassRLC.pdf · Rick...
On-Wafer Measurements in RFIC Design
Rick CampbellDesigner
Portland State University
Abstract:
This talk will cover three closely related topics: a quick overview of the different roles of high frequency on-wafer probing in engineering and production test; some details of high frequency calibration; and practical approaches to on-wafer measurement as an engineering tool during the design and development of mm-wave and sub-mm wave RFICs.We begin by discussing the need to probe engineering prototype RFICs in an era when package models are routinely included in IC design software. Why not just design everything right the first time, and use on-wafer tests to discard bad parts and wafers before packaging?Having established the need for measuring engineering prototypes, we move on to some issues with calibration, starting with a very quick review of the fundamentals: What is Cal? Why a 50 ohm environment?Why is it hard at high frequencies? Finally we turn to practical issues of on-wafer measurements at mm and sub-mm waves, including the high cost of everything, the need for mechanical precision, and high losses in interconnecting cables and waveguides. These daunting challenges may appear insurmountable in an RFIC business unit working its way up through the frequency spectrum, but these advanced measurements are now routinely practiced in advanced development labs.
Three uses of on-wafer probing:
Traditional
1. Modeling
Measure new devices, structures, processes to obtain constants and statistics for math models
Designers use models in simulators to develop circuits
For expensive processes, long fab times, and complex circuits, designers are totally dependent on the simulator
When things don’t work, it’s not a problem with the simulator...
Test Structure
Three uses of on-wafer probing:
Traditional
2. Production test
Multi-chip modules and expensive packages require Known Good Die
Economics favor testing simple ICs in plastic packages anddiscarding bad ones
But when die are delivered as the product, or used in-house as components of hybrid modules, tested die are needed
Three uses of on-wafer probing:
Less traditional:
3. RFIC Design and development -- This Talk
Engineering prototype integrated circuits historically wirebonded to prototype boards and connected to stacks of manual test equipment for evaluation
After functionality confirmed, small prototype run packaged for engineering evaluation, test circuit development, apps engineering, etc.
...this does not work at high frequency
Typical UHF RFIC circa 2000
Die connected to outside world using 1nH inductors
bond wire 1nH1 GHz j6.28 ohms10 GHz j62.8 ohms100 GHz j628 ohms
Some things a designer needs to know:
It is expensive--do we really have to do it?
1. Justify expense
OK, I’m convinced...but I don’t know anything about it. What are the basics, what is “cal” and how do I interpret results
2. Understand the basics
My company has never done anything above 30 GHz... does anything really work up there?
3. Enough experience to believe it works
10k
100n
12t T37-6
1n
510
47
10
51
2020
L1
L2
1p
16.7 MHz+2 dBm in
L1, L3
12t : 2t T37-6L2, L4
2N5179
12 v 5 mA
50.1 MHz
50.1 MHz+12 dBm out
120
51 chip
2020
L3
L4
1p
J310
12 v 6 mA
jumper or key
100k
1n
1n
10
Typical VHF Circuit
Near-perfect grounds
Typical VHF Circuit
Near-perfect grounds
Note: FR-4 is a viable RFIC substrate
Three circuit elements that don’t exist at higher frequency:
Wire
Ground
DC sources
It really isn’t all about the transistors!!!
Low DC Power 40m ReceiverRick Campbell 15 Mar 2009
H1 7 MHz 50 ohm quadrature hybrid: 18 turns bifilar on T37-2 (1.1 uH) and two 220 pF capacitors. L1 and L2 12 turns FT37-43. T1 8 turns trifilar on FT37-43. JFET Hartley VFO component values determined experimentally: see many examples in EMRFD. Gain from antenna input to 50 ohm head-phone output is 50 dB: use good antenna and sensitive headphones
This receiver was designed and built as an exercise in sustainable radio engineering: minimum DC power requirements with fundamental concepts, components and techniques that have been around for 50 years and will still be useful for another 50. Performance falls in the wide gap between minimalist designs and good basic receivers such as the microR2. The major performance compromises to achieve ultra-low DC power with common components are opposite sideband suppression, gain, and 2nd and 3rd order dynamic range. Gain and dynamic range limitations may be addressed by using a full-sized elevated dipole antenna fed with ladder line and a high Q impedance matching network such as a Johnson Matchbox. Suppression of an interfering signal or carrier on the opposite sideband may be achieved by adjusting the input Pi network and IQ balance pot to null the offending signal. Experiments are in progress to reduce the power consumption of the Local Oscillator.
L3
730pF
51
2uH
C1 2.7
J310
1N4148100n
1002.2k
33mH
12k
3.9k
680p
2N3904
2N3904
3
1
2
7
5
6
1.8k27k
27k
3.3k430p
768k
487k
+
+
33u
33u
1u680n
3.9mH
100u+
22k
10k
22n
2N3906
2N3906
12k
3.9k
680p
2N3904
2N3904
1.8k27k
27k
3.3k430p
196k
124k
+
+
33u
33u
1u680n
3.9mH
22k
10k
22n
2N3906
2N3906
2Q4
+100u
1k8
10 390
270
4.5v
4v
220k
220k
33u
+ 1.5uF
T1
10nF
51
730pF10nF
T2
H1
L1
L2
1N4148
1M
C2
9v 4 mA
IQ Diode Detector
Local Oscillator
B&W
4v 2.5 mA
10k
This single sideband receiver does not have any amplifiers at the signal frequency. It can be built at 7 MHz or 700 GHz
Frequency Scalable Receiver Architecture
MF to UHF transformers and inductors
Inductors and transformers are easier at higher frequencies
Frequency Scaling Works -- but there are limits:
1mm square LNA die at 1 GHz
1um square die at 1 THz
It really isn’t all about the transistors!!!
with 650um bond wires -- 650 pH
with 650nm bond wires -- 650 fH
Frequency Scaling--walking up the bands
Circuit board at 2.3 GHz -- 1mm square die at 60 GHz
Signal In Signal Outsignal path on die
DC and control
DC and control
sub-mm wave RFIC die
Probe in and out
Bond Die to board
DC and control
Works at 500 GHz
App circuit mimics wafer probes
Signal In Signal Out
What an RFIC Designer really needs to know about on-wafer measurements...
...so he can explain it to managment
0.10.1
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1010
10
2020
20
5050
50
0.20.2
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0.40.4
0.40.4
0.60.6
0.60.6
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0.80.8
1.01.0
1.01.0
20-20
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90-9
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0.10.1
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0.120.120.13
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RADIALLY SCALED PARAMETERS
TOWARD LOAD ó> <ó TO WARD GENERATOR1.11.21.41.61.822.5345102040100
SWR 1∞
12345681015203040dBS
1∞
1234571015 ATTEN. [dB]
1.1 1.2 1.3 1.4 1.6 1.8 2 3 4 5 10 20 S.W. L
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1 ∞0 1 2 3 4 5 6 7 8 9 10 12 14 20 30
RTN. LOSS [dB] ∞
0.010.050.10.20.30.40.50.60.70.80.91
RFL. COEFF, P0
0.1 0.2 0.4 0.6 0.8 1 1.5 2 3 4 5 6 10 15 RFL. LOSS
[dB]
∞0
1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.5 3 4 5 10 S.W. P
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RFL. COEFF, E or I 0 0.99 0.95 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 TRANSM. C
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ORIGIN
Black Magic Design
The Complete Smith Chart
Gaaaahhhh!
Simplified
Can study basics just using S11
Hi ZLow Z
Inductance
Capacitance
length = mag S11
Ignore all the lines
The Smith Chart is just a polar plot of S11
Series X
Shunt X
Transmission Line
Start anywhere
add:seriesshuntTL
MeasuredData presented on the Smith Chart show the Designer how to fix things
Manager view of Smith Chart
very useful
1.0
20 dB Return Loss
0.80.6
0.40.2
10 dB Return Loss1.00.80.60.40.20.0
0.
00
Bad Design
Good Design
Note the spread: Solutions on the Smith Chart are not points. They show statistical variations and how results vary with frequency.
Manager view of Smith Chart
The Sky is Falling!
Verymisleading!
...which leads us to...
What an RFIC Designer really needs to know about calibration...
...so he can explain it to managment
Open with 1dB attenuator
Open
Cal is your friend
Frequency sweep of a 1 dB attenuator and an open circuit length of transmission line
Open with 1dB padcalibrated outand small errors
Multiply magnitude of S11 by 1.58489 at every frequency
That’s silly--it was measured data--too many decimal places
After cal, the entirely passive system appears to be unstable
Measurements of entirely passive systems with open and/or short circuits and lossy transmission lines often wander beyond the edge of the Smith Chart.
The sky is not falling.
SeriesInductor
ShuntCapacitor
Cal is beyond complex
The effect of stray Inductors,Capacitors, transmission line lengths depend not only onfrequency, but also where you start on the Smith Chart
SeriesInductor
ShuntCapacitor
Why 50 ohms?convenient transmission lines
at low Zinductance dominates
at high Z capacitance dominates
On-Wafer Measurements at sub-mm waves:
Different Behavior Dominated by Electromagneticsand the physical size of electrical degrees:
Small, precision mechanical pieces are expensive...
Coax and Connectors
Garden variety SMA connectors ~22 GHz
0.5mm Coax Connectors good to 110 GHz
~$1k per mated pair, limited life
Coax 20mil coax single mode to 270 GHz
but attenuation many dB per inch...
Above 110 GHz
waveguide to probes, coax or waveguide to membrane tip
At 300 GHz, free space half-wave dipole is 500 microns long...
250 microns is halfway around the Smith Chart
Where you land on a set of 100 micron bond pads can make large excursions on Smith Chart--need to land exactly the same place on cal structure as on test structure
At what freq can you start to see granularity of photons?
1 Hz bandwidth1Kelvin1.38x10^-23 Joule/K
1 photon per second6.626×10−34 Joule-Seconds
hf = kT
solve for f
at 1K f=20.8 GHz
at 3K cosmic background 62 GHz
at room temperature 6 THz
green light 538nm frequency 560 THz
Wait... are sub mm-waves photons? Little billiard balls that pop out of the probe tip one at a time?
Conclusions:
The sky is not falling when statistical variations in cal coefficients and measured data take us beyond the edge of the Smith Chart
mm-wave hardware is expensive but capable
We need on-wafer measurements as part of RFIC Design at high frequencies
The fundamentals are pretty basic
Cal is complex, but simple to understand