1. 1 1.3 V low close-in phase noise NMOS LC-VCO with parallel PMOS transistors Moon, H.; Nam, I.; Electronics Letters Volume 44, Issue 11, May 22 2008 Page(s):676 - 678 Digital Object Identifier 10.1049/el:20080404 Electronics LettersIssue 11 Student : ming-long chuang Date:12/28/2009 National Changhua University Department of Graduate Institute of Integrated Circuit Design

2. 2 Outline  Abstract  INTRODUCTION  Circuit design  Experimental results  Conclusion

3. 3 Abstract  A new NMOS cross-coupled LC-VCO with parallel PMOS transistors is proposed. The proposed LC-VCO is useful for suppressing flicker noise up conversion and very suitable for low voltage application.  It is implemented in 0.18 mm CMOS technology.  Measured phase noise is -93 dBc/Hz at 100 kHz and -116 dBc/Hz at 1 MHz offsets and its core current is only 2 mA for a 1.3 V supply voltage..

4. 4 INTRODUCTION  The 1/f^3-shaped phase noise close to the carrier in a CMOS LC VCO is dominated by flicker noise up conversion.  The two major mechanisms are the 1/f noise in the tail current source transistor and the differential pair FETs.  Recent reports have elaborated various techniques for suppressing the 1/f noise up conversion in CMOS LC oscillators.

5. 5 INTRODUCTION  To suppress flicker noise up conversions from a bias transistor and a differential pair, we need to replace a bias transistor with a poly silicon resistor that has no 1/f noise.  In addition, a decoupling capacitor can be used to obtain a negligible second- harmonic voltage at the source nodes as a source-coupled multi vibrator.  Two inductors are needed to provide a high level of impedance without degrading the Q-factor of the LC tank.

6. 6 INTRODUCTION  The complementary LC-VCO, which is used to exploit the symmetry of the oscillator circuit, is also useful because it can minimize the up conversion gain of low frequency noise.  This Letter propose a new technique for suppressing flicker noise up conversion in an LC-VCO. It is viable for a low supply voltage because the stacked PMOS transistors are not required to maintain a symmetric waveform characteristic.

7. 7 Circuit design  To improve the close-in phase noise characteristic of an NMOS LC-VCO, we focus on a differential pair.  The flicker noise of the differential pair modulates the second-harmonic voltage waveform at its common-source node.  To suppress the 1/f noise up conversion from differential pair transistors, we propose an NMOS LC-VCO structure with parallel PMOS transistors.

8. 8 Circuit design  Schematic of proposed LC-VCO

9. 9 Circuit design  Voltage waveforms at tail current-source node

10. 10 Circuit design  Phase noise characteristics with ideal current source

11. 11 Circuit design  Phase noise characteristics including 1/f noise of tail bias transistor

12. 12 Experimental results  The proposed NMOS LC-VCO with parallel PMOS transistors was designed and fabricated in 0.18 mm CMOS process. To verify the performance of the proposed LC- VCO and to compare it with a conventional complementary LC-VCO, we implemented two LC-VCO under the same conditions, such as an LC tank and a bias current.

13. 13 Experimental results  Chip photograph of proposed LC-VCO

14. 14 Experimental results  Measured phase noise performance of proposed LC- VCO and complementary LC-VCO

15. 15 Conclusions  The proposed NMOS LC-VCO with parallel PMOS transistors can reduce flicker noise up conversion from differential pair transistors and tail bias current transistors.  The proposed LC-VCO is fabricated in 0.18 mm CMOS process, and has a low close-in phase noise performance and is very suitable for a low supply voltage.

16. 16  Thank you for your attention