The Effect of Substrate Noise on VCO Performance

Transcription

1 (RTU4A-1) The Effect of Substrate Noise on VCO Performance Nisha Checka, David D. Wentzloff, Anantha Chandrakasan, Rafael Reif Microsystems Technology Laboratory, MIT 60 Vassar St. Rm Cambridge, MA, (USA) RFIC - Long Beach June 12-14,

2 Outline Motivation/Background Noise Characterization Test Chip VCO Results Effect of Bias Current Effect of Guard Rings Conclusions RFIC - Long Beach June 12-14,

3 What is Substrate Noise? Digital circuits inject noise into substrate during switching Noise propagates to analog section via substrate Effect on analog circuits: substrate contacts, pickup through large capacitive nodes, backgate effect RFIC - Long Beach June 12-14,

4 Motivation UWB transceiver chip TSMC 0.18 µm mixed mode process Digital OFF Digital ON RFIC - Long Beach June 12-14,

5 Noise Characterization Test Chip TSMC 0.18 µm mixed-mode process (non-epi substrate) ρ sub Ωcm Triple-well process (~ 20 db isolation) 2.4G n+ 5.2G n+ 900 MHZ GR 900 MHz p+ sense 2.4 GHZ GR2 2.4 GHZ GR1 2.4 GHZ 5.2 GHZ GR 5.2 GHZ 900M n+ Die Microphotograph of Test Chip RFIC - Long Beach June 12-14,

6 Experimental Setup Multiple injection/sensing locations Three VCO center frequencies RFIC - Long Beach June 12-14,

7 Parameters VCO center frequency 900 MHz, 2.4 GHz, 5.2 GHz VCO bias current Isolation No guard ring, guard ring RFIC - Long Beach June 12-14,

8 Noise Coupling Paths I VCO V DD /GND V out V CTRL substrate inductorsubstrate capacitance substrate noise RFIC - Long Beach June 12-14,

9 Noise Reception 5.2 GHz VCO (no GR) I VCO V cont Power (dbm) db gain by powering up P=-60 dbm P=-72.2 dbm Noise injection frequency VCO off VCO on -85 sub sub Frequency (GHz) Noise couples through GND line and inductor-substrate capacitance RFIC - Long Beach June 12-14,

10 Inductors 900 MHz 2.4 GHz 5.2 GHz L = 11.4 nh C = 220 ff A 340 x 340 µm 2 L = 3.19 nh C = 100 ff A 220 x 220 µm 2 L = 655 ph C = 38 ff A 140 x 140 µm 2 Noise coupling through inductor decreases RFIC - Long Beach June 12-14,

11 Noise -- Inductor Component Inductor Noise Coupling db 5.2 GHz VCO 900 MHz VCO Power (dbm) Frequency (MHz) RFIC - Long Beach June 12-14,

12 Parameters VCO center frequency 900 MHz, 2.4 GHz, 5.2 GHz VCO bias current Isolation No guard ring, guard ring RFIC - Long Beach June 12-14,

13 Effect of VCO Bias Current 5.2 GHz VCO Phase Noise Level (dbc/hz) Low Mid High I LOW I MID = 1.81 ma = 2.71 ma I HIGH = 3.41 ma I BUFF = 2.73 ma khz 1 MHz 10 MHz Frequency Offset I VCO 1.81 ma 2.71 ma 3.41 ma P c /P n (db) 9.9 db 26.3 db 23.1 db Ratio of carrier to noise power for 5.2 GHz VCO RFIC - Long Beach June 12-14,

14 Parameters VCO center frequency 900 MHz, 2.4 GHz, 5.2 GHz VCO bias current Isolation No guard ring, guard ring Dual guard rings RFIC - Long Beach June 12-14,

15 Effect of Guard Rings Guard rings only surround active devices Can only attenuate ground component of noise Guard rings RFIC - Long Beach June 12-14,

16 Guard Rings and Inductor-Sub Noise Guard ring has no effect on inductor component -60 Guard Ring -60 No Guard Ring dbm dbm Power (dbm) Power (dbm) Frequency (MHz) Frequency (MHz) Test: VCO powered off. Noise injected at 900 MHz RFIC - Long Beach June 12-14,

17 Effect of Guard Ring for 5.2 GHz VCO 0 Received Noise for 5.2 GHz VCO -5 no GR GR -10 Power (dbc) foffset (MHz) RFIC - Long Beach June 12-14,

18 Guard Ring Attenuation 900 MHz: db to db 5.2 GHz: db to 0.64 db Guard Ring Attenuation 0 900M Power (dbc) GHz 5.2 GHz IM1 900M IM1 5.2G IM1 5.2G 900 MHz MHz IM foffset (MHz) RFIC - Long Beach June 12-14,

19 VCO Locking As f noise approaches f VCO, and if P noise is comparable to P carrier, VCO can lock to f noise 5.2 GHz VCO Spectrum -25 Free-running VCO No Noise Power (dbm) Frequency (GHz) RFIC - Long Beach June 12-14,

20 VCO Locking As f noise approaches f VCO, and if P noise is comparable to P carrier, VCO can lock to f noise 5.2 GHz VCO Spectrum -25 VCO locked to f noise = GHz Locked Power (dbm) Frequency (GHz) RFIC - Long Beach June 12-14,

21 VCO Locking As f noise approaches f VCO, and if P noise is comparable to P carrier, VCO can lock to f noise 5.2 GHz VCO Spectrum -25 VCO locked to f noise = GHz Free-running VCO No Noise Locked Power (dbm) Locked to noise 20 khz away Frequency (GHz) RFIC - Long Beach June 12-14,

22 Resonant Gain Behavior Received Noise for 5.2 GHz VCO 0-5 no GR GR -10 Power (dbc) foffset (MHz) RFIC - Long Beach June 12-14,

23 VCO Locking Range f [1] lock fo 2Q I I noise carrier No GR/GR f center Locking Frequencies Range No GR GHz GHz 50 khz GR GHz GHz 5.2 GHz VCO and Injection Locking 20 khz No GR/GR f center Locking Frequencies Range No GR GHz GHz 50 khz GR GHz GHz 2.4 GHz VCO and Injection Locking 30 khz No GR/GR f center Locking Frequencies Range No GR MHz MHz 5 khz GR MHz Doesn t Lock 900 MHz VCO and Injection Locking - [1] (Razavi, JSSC, 39(9)) Guard rings improve VCO locking RFIC - Long Beach June 12-14,

24 Conclusions Phase noise of a VCO is adversely affected by substrate noise In extreme, VCO can lock to noise Bias current plays important role Guard rings are effective at lower frequencies, less useful at higher frequencies RFIC - Long Beach June 12-14,