1. TU3E-4
A K-band Low Phase-Noise High-Gain Gm Boosted Colpitts VCO for GHz FMCW Radar applications
R. Levinger, O. Katz, J. Vovnoboy, R. Ben-Yishay and D. Elad
IBM Research – Haifa Labs, Haifa, Israel
TU3E-4

2. Transmitter and VCO design Measurements
Outline
Introduction
Transmitter and VCO design
Measurements
Comparison to state of the art K-band VCO’s
Summary
I will start with a short introduction, then review the synthesizer with an emphasis on the sub-integer divider, low noise CP and the low phase noise VCO. I will than present some of our measurements to demonstrate the low phase noise and low spurious response of this synthesizer. I will conclude this talk with a comparison to state of the art K and Ku band synthesizers.
TU3E-4

3. Introduction 76 – 81 GHz FMCW Radar
For a short range radar (e.g. as a pre-crash sensor) a high resolution is needed.
The FMCW resolution is determined by the frequency range ∆𝑅= 𝑐 2∙{𝑡𝑢𝑛𝑖𝑛𝑖𝑔 𝑟𝑎𝑛𝑔𝑒}
Among the available spectra, the GHz range offers large bandwidth, with ideal detection resolution of 3cm.
Phase noise is crucial for long range applications where range correlation have reduced effect: 𝑆 ∆𝜑 𝑓 =4 𝑆 𝜑 𝑓 𝑠𝑖𝑛 2 𝜋𝑅𝑓 𝑐
E-band frequency range starting from 71-76GHz for the lower band and 81-86GHz for the upper band, offers high capacity channels, used for point-to-point wireless applications, mainly in the newly deployed 4G backhul. The E-band frequency range shows lower oxygen absorption then the 60GHz unlicensed band, and therefore can be used for larger transmission distances. Finally, smaller and less expensive chips with high integration levels will enable a wider deployment of E-band transmission systems.
TU3E-4

4. Introduction GF SiGe BiCMOS 8HP
Technology features:
5 metal layers
MIM and FET based capacitors
fT= 200GHz, fMAX= 280GHz
Comparable to 65nm+ CMOS
Mature mmW technology
Fully characterized actives/passives
CMOS - 130nm with pMOS fT> 45GHz
To preserve HBT peak-fT/ peak-gm/min-NF operation point over temperature and process, bias compensating circuits are used.
The designs were fabricated with IBMs SiGe BiCMOS8hp. The HBT’s in this technology have an ft of 200GHz and fmax of 280GHz. The technology also includes 0.13um MOS transistors. The technology is fully modeled up to 110GHz, including passives, S-param measurements that we have conducted show a very good fit up to 170GHz.
TU3E-4

5. System Overview - Why K-band VCO ?
Long et al. “Passive Circuit Technologies for mmW wireless Systems on Slicon”, IEEE transactions on circuits and systems 2012
It was shown by Long et al that there is an optimum of BW % and PN per technology. For technologies comparable to 65 nm CMOS such as the BiCMOS 8hp used in this work the optimum regime lies within 10 to 30 GHz. In the particular case of the SiGe 8hp the optimum can be found between 15 to 20 GHz.
Q increase
Thick oxide n+/n-well varactor
2-layer MIM capacitor
Thin oxide p+/p-well varactor
Backend MIM capacitor
80 fF thin oxide n+/n-well varactor
TU3E-4

6. System Overview 76 - 81 GHz Transmitter
Type-II, 4th order Frac-N Synthesizer with 3rd order Mesh 16-bit Sigma-Delta divider control, and internal chirp control.
3rd order loop filter with a loop band width of ~ 150kHz.
Differential architecture for low reference spur and due to limited logic speed.
Synthesizer loop bandwidth needs to be constant for the whole tuning range to ensure equal settling time for each state
Nominal tuning range widen to 18.7 – GHz, to comply with process and temperature variations.
TU3E-4

7. pMOS Gm boosted balanced Colpitts
Provides low phase noise thanks to its favorable impulse sensitivity function
Improves the start-up condition by a factor of 2+ 𝐶 𝑓𝑖𝑙𝑡 𝐶 𝑐𝑜𝑙𝑝
Reduces noise of active devices into the tank during zero-crossings
Tail filter reduces the phase noise and increases effective negative resistance
Filter was tuned to the second harmonic
pMOS transistors are used since they contribute less drain current thermal noise for the same gm
LC TANK
TU3E-4

8. High Gain Implementation
LTank
LChoke
LFilter
Differential
Output -R
LC TANK
Using a choke inductor to supply VtuneN reduces AM-FM mechanism of white noise injection from the filter and eliminates additional noise generated by frequently used biasing resistor.
TU3E-4

9. Measurement setups Stand-alone VCO chip
2 mm
1.5 mm
VCO
The chip includes VCO, dividers, and output amplifiers.
Setup has external synthesizer to lock the VCO.
VCO and buffer occupy only 0.34mm2
TU3E-4

10. Measurement setup Full E-band Transmitter chip
1.85 mm x4
2.4 mm
PLL
Full E-band Transmitter chip
The chip includes fully integrated synthesizer and frequency multiplier by 4
TU3E-4

11. VCO Tuning Range VCO covers 18.79 to 20.73 GHz.
Measurements show good correlation with the simulation.
TU3E-4

12. VCO Phase Noise
Measurements
@1 MHz off dBc/Hz
@10 MHz off dBc/Hz
Simulations
VCO phase-noise was measured with an external synthesizer on the Stand-alone VCO chip.
The synthesizer was driven to low gain in order to reduce the loop bandwidth < 40 KHz, at its effect on the phase noise.
Good measurement to simulation correlation at high offsets.
TU3E-4

13. VCO Phase Noise
Despite the large gain variance ~ 2GHz/V, phase noise degradation is tolerable ~ 6 dB.
TU3E-4

14. Synthesizer Phase Noise Phase Noise over Carrier Frequency
@1 MHz off dBc/Hz
@10 MHz off dBc/Hz
Phase-Noise Measured at K-band
Measured with the Full E-band Transmitter chip with internal synthesizer
Although the VCO has large gain variation, the synthesizer bandwidth vary by 50 KHz only.
TU3E-4

15. Synthesizer Phase Noise
Phase noise measured across the tuning range.
Less than 2 dB variation in phase noise across the entire tuning range.
TU3E-4

16. Chirp Generation 8 GHz triangular chirp with a slope of 30 MHz/ms.
Measured at L-band, sampled at the synthesizer output and using an internal divide by 16.
8 GHz
@ E-band
300 ms
8 GHz saw tooth with a slope of 30 MHz/ms and
Recovery time of 15 ms.
8 GHz
@ E-band
300 ms
15 ms
TU3E-4

17. E-band Measurement
Output power at E-band with the full transmitter chip (synthesizer + multiplier) is above 8.4dBm across GHz range.
TU3E-4

18. Comparison to state of the art K-band VCO’s
Technology
Center Frequency
Tuning Range (%)
10MHz
(dBc/Hz)
Pdc (mW)
Ref.
(GHz)
Cont.
banded
SiGe 0.13μm
19.76
9.8 -
-132.5 58
This work
17.2
1.75
23.3
-133 52
RFIC 2015
19.9 11
-129
200
SiRF 2014
19.3
12.4
-130 23
SiRF 2013
CMOS 65nm
25.3
23.2
34.8
-119
4.1
IMS 2015
CMOS 90nm
20.9
3.1
6.2
TMTT 2012
SOI 32nm
24.7 5
-124 24
JSSC 2013
CMOS 130nm
9.4
-133* 3
RFIC 2009
Comparison to other state of the art Ku synthesizers show that this has excellent phase noise performance and very high division ratio and number of states.
* Phase noise only specified at 23.3 GHz.
TU3E-4

19. Summary
A low phase noise and high gain K-band VCO for GHz FMCW radar application was fabricated in GF 130nm SiGe BiCMOS process.
The VCO covers to GHz continuously, allowing full coverage of the 76 to 81 GHz range when followed by frequency multiplier by 4.
VCO Phase 10 MHz offset is to -140 dBc/Hz at K-band .
A 8 GHz chirp at E-band with 30 MHz/ms slope (triangle and saw tooth) have been demonstrated using the Frac-N synthesizer.
TU3E-4