Proceedings of the 8th European Microwave Integrated Circuits Conference
A 159-169 GHz Frequency Source with 1.26 mW Peak Output Power in 65 nm CMOS Bassam Khamaisi and Eran Socher School of Electrical Engineering, Tel-Aviv University Tel-Aviv, Israel
[email protected]
Abstract— This paper present a D-band signal source based on a 2nd harmonic generation of a differential Colpitts VCO that fabricated on 65 nm CMOS process. It covers a frequency range from 159 GHz to 169 GHz with a total tuning range of 5.8%. It provides -3.8 dBm at 163.5 GHz with a nominal supply voltage of 1.2 V while consuming a DC current of 25 mA and with power efficiency of 1.38%; increasing the supply voltage to 2 V with consuming a DC current of 44 mA achieves +1 dBm at 164.6 GHz with efficiency of 1.43%. The source performance in terms of output power, tuning range and efficiency is the best that reported on CMOS at this frequency range. Keywords— Colpitts topology, CMOS, D-Band, Millimeter waves, Voltage Controlled Oscillator (VCO).
I.
desired operation frequency is very close to the process fmax of 175 GHz, push-push operation is preferred to a fundamental source. Even if fundamental operation is possible, the resulting output power and tuning range would be low. Section II describes the circuit design principle and details; section III presents the measured results of the signal source and in section IV we conclude. II.
CIRCUIT DESIGN
Fig. 1 shows the schematic of the signal source based on differential Colpitts VCO.
INTRODUCTION
Millimeter wave (mm-wave) frequency range presents a great potential for non-invasive passive and active imaging, biochemical spectroscopy, high data rate communication and short radar range [1]. The first step toward realization of mmwave system for the mentioned applications above is to be able to design a high power, tunable and wide range signal source. Traditionally, mm-wave signal sources are composed of a tunable frequency signal source, a chain of Schottky diode multipliers and amplifiers in compound semiconductors. These signal sources generate more than 0 dBm in the mmwave band but they are bulky, high cost and complex for integration [2]. Despite the limited power gain frequency product, the limited cutoff frequency and the low breakdown voltage of transistors on solid state electronics, the latest advances of CMOS technology have made it a potential candidate for implantation of compact and low cost mm-wave sources. Recently, several integrated circuits demonstrated frequency generation above 100 GHz using both SiGe and CMOS technologies. Based on either fundamental VCO topology or push-push principles for harmonic generation [3], [4], these designs suffer from lack in terms of tuning range and output power. In this paper, we report a signal source operating around 165 GHz in 65 nm CMOS, with emphasis on achieving high output power and wide tuning range. Based in our pervious works [5], [6], [7], the proposed signal source design is based on push-push technique of a fundamental VCO, where fundamental frequency tuning is easier and transistors can be implemented larger to allow higher output power. Since the
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Fig. 1 Schematic view of the VCO.
The oscillator consists of two parts. First part is the oscillator core formed by the transistors (M1 and M2). Second part is the LC tank. The transistors are RF NMOS transistors with an fmax of 175 GHz extracted by a simulation at nominal supply of 1.2 V. In order to ensure oscillations on the steady state, the oscillator core has to generate a sufficient negative resistance to compensate the ohmic loss in the LC-tank and the transistor itself. The negative resistance is seen from the LC-tank (Ls and Cs) with the help of the feedback of Lg and the transistor gate-source capacitance Cgs. The oscillator frequency is determined by the effective tank composed mainly by Cgs, Lg, Ls and Cs [7]. The fixed capacitor Cs is implemented using finger MetalOxide-Metal (MOM) capacitor structure. Oscillation frequency tuning based on transistor internal capacitance was preferred to tuning based on additional varactors due to the
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low Q of MOS varactors at high frequency which leads to a dramatic performance degradation and limits the available tuning range. Tuning the oscillator frequency is achieved using the change in Cgs induced by the gate and drain bias that control the effective channel length. Increasing the gate voltage tends to increase Cgs (thus decreasing the oscillation frequency) and increasing the drain voltage tends to decrease Cgs (thus increasing the oscillation frequency). In the proposed topology, there is no need to add an output buffer stage to drive the load since the tank is placed between the gate and the source and the output is at the drain of the transistors. Hence the oscillation frequency is not sensitive to the output load impedance and the oscillator transistors provide a buffering effect. Moreover, this topology allows the use of large transistors in order to generate a more powerful fundamental signal due to the weak loading impact of the drain-source transistor capacitance. On this design, the ground on the center tap of Ls improves the common mode. Both the inductor Lch and the capacitor Cout provide a bias T, with Lch the DC supply can be applied to the center tap of Ld, while Cout extracts the 2nd harmonic of the oscillator from the drains to the 50 Ω load. Both the drain inductor Ld and the capacitor Cout were optimized to maximize the 2nd harmonic output power on the load. Although Lch is used as a RF choke to the output signal, this inductor is considered as part of the output power optimization while keeping its self resonance frequency (SRF) above the output frequency. On the DC lines connected to the center tap of Lg, accumulation mode MOS capacitors were connected for decoupling. All of the passive components, namely inductors and finger capacitors, as well as the RF and DC lines and pads were simulated in ADS Momentum electromagnetic simulator, while the circuit schematic after parasitic extraction was simulated in Goldengate. III.
around 165 GHz were used to measure the output signal. The output frequency, the tuning range and the phase noise were measured by connecting an Agilent E4448A spectrum analyzer (PSA) at the IF test port of OML WR-06 frequency extension module (connected to Agilent E4361C PNA for voltage supply), the LO signal was provided to OML module by an Agilent E8257D signal generator (PSG) and connected to the LO input port. The RF signal at the VCO output GSG pads was provided to the output test port (WR-06 waveguide) of the OML module by the GSG probe and the waveguide section. The RF signal was down converted by the OML module with harmonic number of 10, where the LO frequency is around 16 GHz.
Fig. 2 Die micrograph of the VCO (area of VCO core 200 μm x 120 μm).
Fig. 4 shows the IF signal seen on the spectrum analyzer after a 165 GHz RF signal was down converted by OML WR06 extension module, where the DC power consumption is 88 mW from Vdd=2 V and Vg=1.4 V.
MEASUREMENT RESULTS
The proposed VCO was fabricated in a commercial 65 nm 1P9M UMC CMOS process, which provides one poly layer for the gates of CMOS transistors and nine metals, including an ultra-thick copper top metal (metal 9) of 3.25 μm. Fig. 2 shows the chip micrograph of the VCO. The inductors Lg, Ls and Ld are built using single loop inductors; their traces were formed using the top metal 9 layer, in order to maximize their quality factor Q. The inductors Lg and Ls are nested to save silicon area and improve symmetry. Mutual coupling between the symmetrical halves of these inductors is instrumental in generating a differential fundamental signal. The VCO started to oscillate at a bias current of 8 mA with Vdd=1 V and Vg=0.8 V. For more stable oscillation and larger output power, the measurements were performed on higher Vdd values. The output frequency is measured using the setup shown on Fig. 3. A Cascade Infinity WR-06 GSG probe connected to a waveguide section both with 4 dB total loss at
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Fig. 3 Characterization setup for output oscillation frequency measurement.
To explore the VCO oscillation frequency limits, Fig. 5 depicts the output frequency versus the tuning voltage Vg. Additional tuning is provided by the supply drain voltage, both controlling Cgs. Allowing Vdd and Vg to reach 1.8 V and 2 V respectively, the output frequency can be tuned from 159.2 to 168.8 GHz, amounting to about 6% of total tuning range. Increasing the gate and drain bias increases the DC power consumption up to a maximum of 130 mW. The output frequency at this maximal DC consumption, 164 GHz sits at mid-band, where it could easily be achieved using lower Vg and Vdd, as seen in Fig. 5.
GHz, reaching a power efficiency of 1.38%. Moreover, at nominal supply, the signal source provides -7.8 to -3.8 dBm on the frequency range from 159.5 to 165 GHz. Increasing the supply voltage to higher voltages achieves more output power, up to +1 dBm at 164.6 GHz with Vdd=2 V, Vg=1.4V while consuming DC current of 44 mA, achieving a power efficiency of 1.43%.
Comparison between measured and simulated results shows a slight frequency shift up (about 2%); probably this could be attributed to inaccurate parasitic extraction at these frequencies for this CMOS process, which is validated only up to 20 GHz.
Fig. 4 The IF signal is shown on the spectrum analyzer after a 164.6 GHz RF signal was down converted by a OML WR-06 extension module with harmonic number of 10 and LO frequency of 16.45 GHz. Fig. 6 Output power versus gate voltage with Vdd of 1.2 V (black) and 2 V (blue) in simulation (line) and measurement (markers).
From Fig. 4, the phase noise can be estimated as -73 dBc/Hz at a 5 MHz offset, compared to a simulation result of -120 dBc/Hz at a 5 MHz. It should be noted that the phase noise measurement is pessimistic because it includes the contribution of the phase noise of the WR-06 OML TR module used for down conversion [8]. Table I summarizes the performance of the signal source presented in this paper and compares it with recently reported signal sources in similar frequency ranges using different technologies. This signal source demonstrated the best performance on CMOS technology reported till now. Fig. 5 Measurement of output frequency versus Vg.
IV.
The output power was measured using a calibrated Microtech Instruments free-space terahertz absolute pyroelectric power meter. A WR-06 waveguide-section connected one side to the GSG probe while the other side (acting as an open waveguide antenna) illuminates the power meter. On-off keying of Vg at 10 Hz provides radiation chopping that is needed for detection using the pyroelectric power meter. The 90 GHz cutoff frequency of the WR-06 waveguide prevents the fundamental frequency power from affecting the output power measurement. The loss of the GSG probes and the waveguide were de-embedded from all power measurements. Fig. 6 shows the output power measured by the power meter versus the gate voltage. At nominal Vdd, a maximal output power of -3.8 dBm is achieved at Vg=1 V with 25 mA at 163.5
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CONCLUSION
A signal source around 165 GHz in a 65-nm CMOS process has been presented. The proposed signal source achieves the widest tuning range on CMOS with 5.8%. Moreover, the proposed source introduces the highest output power of +1 dBm at 164.6 GHz; and the highest power efficiency of 1.43%. The signal source performance in terms of output power, tuning range and power efficiency is the best that demonstrated on CMOS technology at this frequency range.
TABLE I SIGNAL SOURCES BASED VCO COMPARISON Approach
This work
[12]
[3]
[4]
[9]
[8]
[10]
[11]
Colpitts
Cross coupled
Colpitts
Cross coupled
Colpitts
Colpitts
Push-push
Cross coupled
Push-push
Fund.
Fund.
Fund.
SiGe
SiGe
SiGe
SiGe
218-245
183.3-190.5
144.5-157.5
Push-push Technology
65 nm
65 nm CMOS
90 nm
45 nm
CMOS
SOI CMOS
283-295
195.2-198
-
157.3-164.9
CMOS Freq. range [GHz]
159.2-168.8
Fund.
Center freq.[GHz]
164.6
290
196.5
189
161.5
236
190
157
Tuning range
5.8 %
4.5%
1.4%
-
4.7%
11.7%
3.9%
8.6%
Pout [dBm]
+1
-1.2*
-19
-27
-15
-3.6
-4.5
3
Power efficiency
1.43%
0.23%
0.04%
0.012
0.07%
0.8%
0.16%
1.29%
46.5
54
DC power [mW]
88
325
29
16.5
Phase noise [dBc/Hz]
-73 @ 5
-78 @ 1
-100.8 @ 1
-
MHz
MHz
MHz
0.1
0.36
0.19
Size [mm2]
-79.2 @ 0.5 -98 @ 10 MHz MHz
0.29
* Power combination of four cross coupled.
REFERENCES [1]
P. H. Siegel, “Terahertz Technology,” IEEE Trans. on Microwave Theory and Techniques, vol. 50, pp. 910-928, 2002. [2] T. W. Crowe, W. L. Bishop, D. W. Porterfield, J. L. Hesler, and R. M. Weikle, II, “Opening the Terahertz Window with Integrated Diode Circuits,” IEEE J. of Solid-State Circuits, vol. 40, pp. 2104-2110, 2005. [3] C. Hong-Yeh and W. Huei, “A 98/196 GHz Low Phase Noise Voltage Controlled Oscillator With a Mode Selector Using a 90 nm CMOS Process,” IEEE Microwave and Wireless Components Letters, vol. 19, pp. 170-172, 2009. [4] E. Seok, C. Cao, D. Shim, D. J. Arenas, D. B. Tanner, C. M. Hung, and K. K. O, “A 410 GHz CMOS Push-Push Oscillator with an On-Chip Patch Antenna,” IEEE Solid-State Circuits Conference, pp. 472-629, 2008. [5] E. Socher and S. Jameson, “A Wide Tuning Range W-band Colpitts VCO in 90 nm CMOS,” Electronics Letters, vol. 47, pp. 1227-1229, 2011. [6] B. Khamaisi and E. Socher, “A 209-233 GHz Frequency Source in 90 nm CMOS Technology,” IEEE Microwave and Wireless Components Letters, vol. 22, pp. 260-262, 2012. [7] B. Khamaisi, S. Jameson and E. Socher, “A 210-227 GHz Transmitter with Integrated On-Chip Antenna in 90 nm CMOS Technology,” IEEE Trans. on Terahertz Science and Technology, vol. 3, no. 2, pp. 141-150, 2013. [8] A. Tomkins, E. Dacquay, P. Chevalier, J. Hasch, A. Chantre, B. Sautreuil, and S. P. Voinigescu, “A Study of SiGe Signal Sources in the 220-330 GHz Range,” presented at the IEEE BCTM, Portland, OR., Oct. 2012. [9] Y. Zhao, B. Heinemann, and U.R. Pfeiffer, “Fundamental Mode Colpitts VCOs at 115 and 165 GHz,” IEEE Bipolar/BiCMOS Circuits and Tech. Meeting, pp. 33-36, 2011. [10] R. Wanner, R. Lachner, and G. Olbrich, “A Monolithically Integrated 190 GHz SiGe Push-Push Oscillator,” IEEE Microwave and Wireless Components Letters., vol. 15, no. 12, pp. 862–864, Dec. 2005. [11] Jahn, M., Aufinger, K., Meister, T.F., Stelzer, A., “125 to 181 GHz Fundamental-Wave VCO Chips in SiGe Technology,” IEEE Radio Frequency Integrated Circuits Symposium, pp. 87-90, 2012. [12] Y. M. Tousi, O. Momeni, and E. Afshari, “A 283 to 296 GHz VCO with 0.76 mW Peak Output Power in 65 nm CMOS,” IEEE Int. Solid- State Circuits Conf. Dig. Tech. Papers, pp. 286-288, Feb. 2011.
539
0.14
0.81
215
154
-73 @ 1
-86 @ 1
MHz
MHz
0.31
-
