Timing Skew Compensation Technique Using Digital Filter with Novel Linear Phase Condition

Transcription

1 Timing Skew Compensaion Technique Using Digial Filer wih Novel Linear Phase Condiion Koji Asami Advanes Corporaion Hiroyuki Miyajima, uyoshi Kurosawa, Takenori Taeiwa, Haruo Kobayashi Gunma Universiy 1

2 Purpose Fine skew adjusmen using a digial filer while mainaining a linear phase condiion in ATE Timing accuracy is imporan o ATE Various digial filers are used for esing analog LSIs Linear phase condiion is required of he digial filer o preserve he analog waveform 2

3 Ouline Convenional linear phase FIR filer Time-shifed ideal filer Consrucion of linear phase filer Applicaion examples Conclusion 3

4 4 Types of Generalized Linear-Phase FIR Sysems (1)Type I symmeric even-order (2)Type II symmeric odd-order (3)Type III anisymmeric even-order (4)Type IV anisymmeric odd-order 4

5 Frequency Characerisics of 4 Types h(nt) Type I Type II Type III Type IV H(e jωt ) (N1)/2 jω(n1)t /2 e s akcos[ ωk ] k N/2 jω(n1)t /2 e s bkcos[ ω (k 1/2)T s ] k1 (N1)/2 j(ω(n1)t /2 /2) e s aksin[ω k ] k N/2 j(ω(n1)t /2 /2) e s bksin[ω (k 1/2)T s ] k1 Phase : 1s order funcion of frequency Delay : depends on number of Taps 5

6 Ouline Convenional linear phase FIR filer Time-shifed ideal filer Consrucion of linear phase filer Applicaion examples Conclusion 6

7 Ideal Filer Response Frequency Response Impulse Response 1. H(jω ) ωs - 2 ω S 2 ω Fourier Transform H(jω ) T s ωs - 2 ω S 2 ω h() 1 sinc π T s ω s 2 T s : Sampling Rae 7

8 Discree-Time Expression k H(j ω-k ω ) s -2ω s -ω s ωs 2ωs ω Fourier Transform FIR is formed All zero h() k T s sinc π k k T s

9 Time Shifed Impulse Response G(jω ) - π π - π G(jω ) π ω ω g G(jω ) ω Δ Only phase changed Impulse response shifed 9

10 Influence o Coefficiens by Time Shif FIR h() k T s sinc π k k Time shif IIR h() k T s Δ sinc π k k 1

11 Ouline Convenional linear phase FIR filer Time-shifed ideal filer Consrucion of linear phase filer Applicaion examples Conclusion 11

12 2 Tap FIR Model T s a a 1 a a 1 1 H(jω ) H(jω ) ωt s /2 a a 1 T s ω

13 2 Tap Delayed FIR Model T s a a 1 a a 1 1 H(jω ) ω a a 1 H(jω ) T s ωt s /2ω

14 2 Tap Delayed FIR Model T s a a 1 a a 1 1 H(jω ) IIR ω H(jω ) T s ωt s /2ω

15 Phase [radian] Gain [db] Comparison of Freq. Characerisic -1 2 Tap FIR Delayed Normalized Frequency (Fs=1.) 2 Tap FIR Delayed Only slope of phase characerisic is changed 15

16 Frequency Characerisic of Proposed Filer g(nt) Type I Type II Type III Type IV j ω(n1)t /2ω e s G(e jωt ) j ω(n1)t /2ω e s (N1)/2 akcos[ ωk ] k N/2 bkcos[ ω (k 1/2)T s ] 1 k (N1)/2 j(ω(n1)t /2 /2ω ) e s aksin[ω k ] k N/2 j(ω(n1)t /2 /2ω ) e s bksin[ω (k 1/2)T s ] k1 Phase : 1s order funcion of frequency Delay : conrollable wih 16

17 Proposed Design Technique FIR wih Desired Characerisic Delayed Ideal Filer Delayed FIR Filer wih Desired Characerisic 17

18 Example of Raised Cosine Filer 61 ap Raised Cosine Filer Delayed Filer (.3 samples delay)

19 Group Delay [samples] Gain [db] Effec of Window Funcion Rec Normalized Frequency (Fs=1.) Hann Window funcion can reduce Gibbs phenomenon 19

20 Novel Linear Phase Condiion of D.F. Original FIR filer has complee linear phase Original FIR filer is band-limied Bandwidh of signal is below Nyquis rae Fine delay can be conrolled using Ideal filer Delayed filer has infinie impulse response Window funcion can consruc FIR effecively 2

21 Ouline Convenional linear phase FIR filer Time-shifed ideal filer Consrucion of linear phase filer Applicaion examples Conclusion 21

22 Applicaion o Quadraure Modulaor cos2 f I DAC s() sin 2 f Q DAC I jq fc 2 Image rejecion raio f fc f c f fc f f 22

23 Adjusmen of I/Q Skew cos2 f I DAC sin 2 f Q adjus DAC s() fc 2 I jq f fc f c f fc f f 23

24 Magniude [db] Magniude [db] Simulaion Resuls Image Signal Normalized frequency (Fs=1.) (a) SSB signal wih I/Q skew Normalized frequency (Fs=1.) (b) SSB signal wih compensaion Delay Compensaion Filer delay Taps Window.1 sampling poins 61 Taps Hann 24

25 Applicaion o Time-Inerleaved ADCs 1 2T S 1 2T S f CLK 1 ADC1 1 2T S 2 1 T S f h 1 1 T S f ADC2 2 h 2 CLK 2 f CLK 1 CLK 2 T s Compensae his componen Timing skew causes spurious componens 25

26 Magniude [db] Magniude [db] Simulaion Resuls Spurious QPSK signal Normalized frequency (Fs=1.) Normalized frequency (Fs=1.) (a) 2ch inerleaved ADC wih.1 samples skew (b) Compensae he skew using 91 aps delay filer 26

27 Conclusion Fine delay conrollable digial filer which mainains desired characerisics is proposed I is applicable no only o Low Pass Filers bu also o Band Pass Filers I can compensae he iming skew of analog modules in ATE 27