Sub-THz CMOS Molecular Clock with 43ppt Long-Term ...€¦ · 29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and
Post on 09-Feb-2021
9 Views
Preview:
Transcript
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
1 of 40
Sub-THz CMOS Molecular Clock with
43ppt Long-Term Stability Using High-
Order Rotational Transition Probing
and Slot-Array Couplers
Cheng Wang, Xiang Yi, Mina Kim, Ruonan Han
Massachusetts Institute of Technology, Cambridge, MA
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
2 of 40
Outline
• Background
• High-order locking for long-term stabilization
• Architecture and circuit design
• Measurement results
• Conclusions
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
3 of 40
Ultra-Stable, Miniaturized Clocks
Synchronization of high-speed
radio access networks
• 5G massive MIMO → σt < 65ns
• Precise positioning → σt < 10ns
• 1-min holdover → Δf
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
4 of 40
Comparison of Portable Clocks
Stability
Cost
Power
Oven compensated crystal
oscillator (OCXO) Chip-scale atomic clock (CSAC)
Chip-scale molecular clock
(CSMC) (This work)
~100mW~100mW~1W
~$10~$1000~$100
~10-11@103s~10-10@103s ~10-11@103s
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
5 of 40
Outline
• Background
• High-order locking for long-term stabilization
• Architecture and circuit design
• Measurement results
• Conclusions
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
6 of 40
Rotational Spectra of Polar Gaseous Molecules
+
-
F
F
E/M torque → molecular rotation
Photon absorption →state transition (J→J+1)
Rotational spectra observed in WG gas cell
EM field
E or M dipole
16O
12C
32S
MW photon
Polar gaseous molecules
Quantized rotational states
16O
12C
32S
16O
12C
32S
16O
12C
32S
RF in RF out
hν J=1J=2
J=3
J=4
J=5
J=6
J=7
hν
~2×105
Q =f0
fFWHM
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
7 of 40
Wavelength Modulation Spectroscopy (WMS)
• K: “open” → rotational spectrometer
VWM(t) = A(t)·sin[2πfpt + Δf·sin(2πfmt + θ0)]
fm - Modulation freq. Δf - Freq. deviation
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
8 of 40
High Order Harmonics of fm
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
9 of 40
High Order Harmonics of fm
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
10 of 40
Multi-Order Dispersion Curves
Nth order dispersion curve ≈ Nth order derivative
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
11 of 40
Multi-Order Dispersion Curves
Odd order curves → zero-crossing point
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
12 of 40
Molecular Clock Locking to Spectral Line Center
Zero-crossing point:
• Kr : Response, [V/Hz]
• Vn : Noise , [V/ Hz]
SNR =Verror,max
Vn
Allan deviation:
Vn
·Kr·f0σy =
2τ≈
N0
·Q·SNRττ - Avg. time
• K: “open” → rotational spectrometer• K: “closed” → Lock to zero-crossing point
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
13 of 40
Proof-of-Concept: The 1st CSMC Prototype
[C. Wang, et al., Nature Electronics, 2018]
• 231.061GHz line of OCS
• 1st order dispersion curve
• Frequency stability:
σy =3.8×10-10@τ=103s
• 66mW DC power.
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
14 of 40
Frequency Stability of Molecular Clock
Short
term
Medium
term
Long
term
VCXO
noise
σy ≈N0
·Q·SNRτ
1
GBW
Temperature dependency
Drift due to Magnetic field
Drift due to Electrical field
Drift due to baseline tilting
• This work: High order locking
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
15 of 40
Asymmetric Line Profile due to Baseline Tilting
+
• Symmetric in theory • THz transceiver response
• Gas cell response
Asymmetric
line profile
Baseline
tilting
Rotational
spectral line
=
• Measured in reality
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
16 of 40
Asymmetric
line profile
Baseline
tilting
1st Order Dispersion Curve w/ Baseline Tilting
Rotational
spectral line
Offset
voltage VOffset
Long-term
clock drift
• Symmetric in theory • THz transceiver response
• Gas cell response
• Measured in reality
1st order
dispersion curve
• Invariant zero-crossing
point under PVT
+
• Voffset is PVT dependent
=
• How to deal with varying
zero-crossing point?
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
17 of 40
• Voffset is PVT dependent• Eliminated by high order
derivative, Voffset ≈ 0
• Invariant zero-crossing
point under PVT
• Varying zero-crossing
point due to Voffset
Offset
voltage VOffset
1st order
dispersion curve
High Order Dispersion Curve w/ Baseline Tilting
+
High order
dispersion curve
Long-term
clock drift
Stability
enhanced
• Invariant zero-crossing
point under PVT
=
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
18 of 40
Idea: CSMC with High-Order Locking
• Simulation: 0.1dB/GHz baseline
tilting → a frequency drift of:
• 5×10-9 for 1st order locking
• 3×10-10 for 3rd order locking
• This work: a chip-scale
molecular clock (CSMC) locking
to high order dispersion curve
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
19 of 40
Outline
• Background
• High-order locking for long-term stabilization
• Architecture and circuit design
• Measurement results
• Conclusions
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
20 of 40
System Architecture
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
21 of 40
TX: 231GHz Cascaded Two-Stage PLL
• Freq. tunability: ~1% of line width fFWHM
• 27GHz (12%) bandwidth for line coverage
• Precise wavelength modulation (WM)
• Δf/fp≈10-5 (Δf ≈2.5MHz, fp=231.06GHz)
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
22 of 40
TX PLL2: 57.77GHz VCO and 231GHz Quadrupler
• Varactor 1: highly-sensitive for large PLL bandwidth
• Varactor 2: low sensitivity for wavelength modulation
• KVCOVaractor 1 / KVCOVaractor 2 ≈ 103
Simulated under
free-running
Simulated
WM response
Varactor 1
Varactor 2
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
23 of 40
TX: Wavelength Modulator (WM)
• 100kHz differential
output voltage
• 3-bit Δf control
• 0.6° phase control
• Low distortion:
spur < -55dB
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
24 of 40
RX: THz Detector and VGA
• Sub-threshold NMOS pair → low noise THz square-law detector
• 2-stage variable gain amplifier
• 65dB max gain / 10-bit control
• AC coupled / monolithic integrated
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
25 of 40
RX: Harmonic Rejection Lock-in Detector (HRLKD)
• Convert Nth harmonic of fm to DC
• Harmonic rejection of ref. clock fref for
low interference and noise-folding
• Reduce flicker noise at DC output
Conventional
Phasor diagram of harmonic rejection mixer
Proposed
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
26 of 40
RX: Harmonic Rejection Lock-in Detector (HRLKD)
• Harmonic rejection > 80dB
• Reduced DC flicker noise• DC offset Vp-Vn ≈10µV (1µV change → 10-10 drift)
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
27 of 40
Chip-to-Waveguide Coupler
• Conventional designs
• Costly external components
• Special process/wafer thinning
• Insufficient TRX isolation
[C. Wang, et al., JSSC, 2018]
E-plane quartz probe
[H. Song, et al., MWCL, 2016]
Integrated dipole couplerDielectric resonator
MMIC Absorber
Dipole
coupler
Dipole
coupler
[D. L. Cuenca, et al., EuMIC, 2017]
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
28 of 40
Slot Array Coupler: Architecture
• Radiates downward into
waveguide aperture
through Si-substrate
• No external components
• No wafer thinning
Simulated E-field distribution
Port 1
Port 2Port 3
Port 4
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
29 of 40
Slot Array Coupler: Simulated Results
• Simulated loss = 5.2dB
• BW3dB = 21%
• 60dB simulated TX/RX
isolation
• 10-9 drift by 60dB isolation
(removable w/ calibration)
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
30 of 40
Outline
• Background
• High-order locking for long-term stabilization
• Architecture and circuit design
• Measurement results
• Conclusions
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
31 of 40
Chip Photo and Packaging
XTAL
• TSMC 65nm CMOS process.
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
32 of 40
Measured RF Power and Phase Noise of TX
• PRF = -9.4dBm w/ slot array coupler
• PLL bandwidth: 27GHz (12%)
• Phase noise : -81.5dBc/Hz@1MHz
• PM-to-AM noise → SNRPN= 84dB
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
33 of 40
Measured WMS Spectrum and RX Performance
• Spectrum of TX probing signal
with wavelength modulation
• NEP of RX w/ slot array coupler:
62.8 pW/ Hz at fm=100kHz
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
34 of 40
Measured Dispersion Curves and Allan Deviation
• 3rd order curve: SNR = 66dB
• VOffset = 4.3μV (256× smaller)
• 1st order curve: SNR = 84dB
• VOffset = 1.1mV
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
35 of 40
Measured Allan Deviation by 3rd Order Locking
• Allan deviation: σy = 3.2×10-10@ τ =1s, 4.3×10-11@ τ=103s
This work: free
running VCXO
1st CSMC: 1st orderCSAC, ISSCC 2011
This work: 3rd order
CSAC, ISSCC 2019
CSAC, Microsemi
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
36 of 40
Measured Temperature and Magnetic Sensitivity
Temperature (°C) Measurement Time (Minutes)
Fre
q.
Dev
. (1
0-9
)
Fre
q.
Dev
. (1
0-9
)
353025 40 45
6
3
0
-6
-3
2
1
0
-1
-20 3 6 9 12
on off on off on off on
15 18 2150 55 65
on: 75Gauss
off: 0 Gauss
avg
60
• Drift < ± 3×10-9 in 27~65 ºC w/ 2nd
order temperature compensation
• Drift < ± 2.9×10-12/Gauss w/o
magnetic shield in CSAC
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
37 of 40
Outline
• Background
• High-order locking for long-term stabilization
• Architecture and circuit design
• Measurement results
• Conclusions
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
38 of 40
Performance Comparison Table
Parameters SiTime [1] Microsemi [3] ISSCC2019 [4] VLSI2018 [5] This work
Mechanism OCXO 133Cs CSAC 133Cs CSAC 16O12C32S MC 16O12C32S MC
Cost Medium High High Low Low
Freq. (GHz) 0.06 4.6 4.6 231.061 231.061
Harmonics N/A 1st order 1st order 1st order 3rd order
σy (τ =100s) 3.0×10-11 3.0×10-10 8.4×10-11 2.4×10-9 3.2×10-10
σy (τ =103s) 4.0×10-11 1.0×10-11 0.8×10-11 3.8×10-10 4.3×10-11
Temp. Drift a ±5.0×10-9 ±5.0×10-10
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
39 of 40
Acknowledgement
• This work is supported by National Science Foundation (CAREER
ECCS-1653100 and ECCS-1809917), MIT Lincoln Lab, Jet Propulsion
Lab (NASA), and a Texas Instruments Fellowship;
• The authors acknowledge Dr. Stephen Coy, Prof. Keith Nelson, and
Prof. Robert Field of MIT for technical discussions and assistance;
• We appreciate the help from Qingyu (Ben) Yang on the experiments.
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
40 of 40
Demo Session 1
Chip Scale Molecular Clock
29.5: Sub-THz CMOS Molecular Clock with 43ppt Long-Term Stability Using High-Order Rotational Transition Probing and Slot-Array Couplers© 2020 IEEE International Solid-State Circuits Conference
41 of 40
Please Rate This Paper
top related