ELECTROOPTIC SAMPLING OF OPTOELECTRONICALLY PHASE-LOCKED 10.0 GHZ MICROWAVE SIGNALS USING SEMICONDUCTOR-LASER DIODES

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In conclusion, an integrated tapped delay line structure consisting of a coplanar waveguide transmission line with Schottky diode peak detector taps has been fabricated. The structure was driven with two pulse compressor circuits producing two 20pS pulse trains. The relative phases of the two inputs were determined from the position along the structure of the collision event as captured by the hold capacitors. Shifts of 1 pS in the trigger input signal were easily detectable during steady state testing of the structure. Improvements in the current resolution should be possible with better pulse compression circuits yielding greater slew rates for input pulses and reduced dispersion due to tap discontinuities by further distribution of the taps along the line. Finally, when coupled with external processing circuitry the C P P D should be capable of picosecond resolution detection of trigger events in one-shot or in steady state.

A c k n o w l e d g m e n t : This work has been supported by DARPA under contract # “14-87-C-0363.

A. BLACK E. OZBAY B. A. AULD D. M. BLOOM

Edward L. Ginrton Laboratory Stanford University Stanford, C A 94305-4085, U S A References

21s June 1991

STEPHENSON, P. s.: ‘Frequency and time interval analyzer measurement hardware’, Hewlett-Packard J., 1989,40, (I), pp. 3 5 4 1 CHU, U. e., ALLEN, M. s., and FOSTER, A. s.. ‘Universal counter resolves picoseconds in time interval measurements’, Hewlett- Packard J . , 1979,29, (12), pp. 2-11

SKOLNICK, M. I.: ‘Receivers, displays, and duplexers’, in ‘Intro- duction to radar systems’ (McGraw-Hill Book Company, New York, 1980). Chap. 9

RODWELL, M. I., BLOOM, D. M., and AULD, B. A . : ‘Nonlinear transmission line for picosecond pulse compression and broadband phase modulation’, Electron. Lett., 1987, 23, (3). pp. 109-1 10

MADDEN, e. J., MARSLAND, R. A., RODWELL, M. J , and BLOOM, U. M . : ’Hyperabrupt-doped GaAs nonlinear transmission line for picosecond shock-wave generation’, Appl. Phys. Lett., 1989, 54, ( I I ) , pp. 101 9-1021

ELECTRO-OPTIC SAMPLING

OF

OPTOELECTRONICALLY PHASE- LOCK ED 10.OGHz MICROWAVE SIGNALS USING S E M I C 0 N D U C T 0 R LASER DIODES

Indexing t e r m Optical measurement, Lasers and laser appli- cations, Photoconducting devices. Phase-locked loops. Electro- optics. Semiconductor lasers

I0.0GHz microwave signals optoelectronically phase locked by a laser-diode-based GaAs : Cr photoconductive harmonic mixer (A = 0.81 pm) have been measured noninvasively using the electro-optic sampling technique with a gain-switched InGaAsP laser diode (1 = 1.3pm).

The electro-optic sampling (EOS) technique’.’ has been shown to be a very powerful tool for measurement of electrical waveforms noninvasively at internal nodes of discrete elec- tronic devices and integrated circuits. Compact laser-diode- based EOS systems have also been demonstrated by several groups r e ~ e n t l y . ~ In these systems, i t is essential that phase coherence or time synchronisation is maintained between the optical probe pulses and the continuous wave (CW) microwave waveform to be measured. Recently, Li e t al.6 demon-

strated optical phase locking of microwave signals up to 1.3 G H z by intermixing microwave signals with the harmonics of the optical probe pulse using the electro-optic effect in

GaAs microstrip circuits. The signals were then displayed using the photoconductive sampling technique.’,” This novel technique is potentially useful for diagnostics of millimetre wave integrated circuits (MMICs) up t o l 0 0 G H z at the wafer level. In a previous Letter,’ we demonstrated optoelectronic phase locking of microwave signals up to 12.01 GHz using a laser-diode-based GaAs : Cr photoconductive harmonic mixer. In this Letter, we report for the first time electro-optic sampling of 10.0 GHz optoelectronically phase-locked microwave signals using semiconductor laser diodes.

Our experimental apparatus is shown in Fig. 1. It consists of an optoelectronic phase-locked loop (OEPLL) and an

Fig. 1 Experimental setup FS: frequency synthesiser PA: power amplifier LF: loop filter SO: sweep oscillator C G : comb generator LD: laser diode LDA: laser diode array PCS: photoconductive switch PBS: polarisng beam splitter QWP: quarter-wave plate HWP: half-wave plate R: receiver LIA: lock-in amplifier

electro-optic sampling system. Two electronically phase- locked synthesisers were used t o gain switch a laser diode array (LDA, Spectra Diode Laboratories, model SLD-2410, I. = 0.81 pm) at f 2 and a n InGaAsP laser diode (LD, Toshiba,

model TOLD-300, I = 1.3pm) at fi, respectively. In the OEPLL, a free running signal at

f,

from a microwave sweep oscillator (HP8620C), simulating the monolithic device, was used to bias a GaAs : Cr switch with 10pm gap and inter- mixed with the appropriate harmonic component of the electrical pulses generated by l00ps optical pulses from the LDA illuminating the switch. The signal at the output port of the switch was amplified by a low-noise 26dB-gain amplifier and mixed with the 10 MHz reference signal of the frequency synthesiser (HP8657A) at f z . The detected error signal was used to phase lock the sweep oscillator which operates as a voltage- controlled oscillator (VCO) via a loop filter. In the present experiment, f i = 250 MHz,

f,

= Nfl, and f z = (Nfl f IOMHz)/M, where M , N are integers. Fig. 1 IS the instrument-limited spectrum of the 10.0 G H z optoelectronically phase-locked signal, exhibiting minimal sidebands.

This signal was either amplitude modulated or chopped with a microwave switch at 1.OkHz and sent to the EOS also shown in Fig. 2. We used the standard reflection-mode probing geometry. A train of 30ps optical pulses from the gain-switched and phase-locked 1.3pm L D was sent through a polarising beam splitter (PBS), a quarter-wave plate (QWP)

* wu, H.-H., CHANG, c.-s., and PAN, c.-L.: ’Optical phase-locking of

microwave signals up to 12GHz by laserdiode-based GaAs : Cr

photoconductive harmonic mixer’, submitted to Electron. Lett., 1991

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and a half-wave plate (HWP) and focused on the ground plane of a GaAs microstrip transmission line used as the

-20 -3 0 -LO -50 -60 - 70 E m TI IO 00000311 frequency, GUz

Fig. 2 Specrrum oJ 10.0 G H z optoelecrronically phase-locked signal

Resolution BW = l00Hz Frequency span = 500 Hz/division Amplitude scale = lOdB/division

sampler. The microwave signal changes the polarisation of the reflected probe beam which passes back through the lens and the waveplates. The probe pulses were then directed by the beamsplitter to a G e photodiode and processed by a lock-in amplifier. Several cycles of the 10,OGHz signal were observed as the optical probe pulses were scanned across the microwave waveform by employing an optical delay line. This is shown in Fig. 3. It is worth noting that the microwave signal

2 WEINGARTEN, K . J., RODWELL, M. J. w., and BLOOM, D. M.: ‘Picose- cond optical sampling of GaAs integrated circuits’, IEEE J . Quanrum Electron., 1988, QE24, pp. 198-220

NEES, J., and MOUROU, G . : ‘Noncontact electro-optic sampling with a GaAs injection laser’, Electron. L e f t . , 1986, 22, pp. 918-919 WIESENFELO, J. M., and JAIN, R. K . : ‘Direct optical probing of inte- grated circuits and high speed devices’, in MARCUS, R. B. (Ed.): ‘Measurements of high speed signals in solid state devices, semiconductors and semimetals’ (Academic press, 1990), Vol. 28, pp.

221-334 (and references therein)

TAKAHASHI, R., and KAMIYA, T.: ‘Application of a diode laser amplifier to an ultrafast desktop electrooptic sampling system’. 1990

Topical Meeting on Optical Amplifiers, Monterey, CA, USA, paper WC4

mixing optical and microwave signals in GaAs microstrip circuits for phase-locking applications’, IEEE Trans., 1990, hflT-38, pp.

I9241 931

Li, M. G., HUANG, s.-L. L., LEE, c. H., and HUNG, H.-L. A . : ‘Display of microwave waveform via a low frequency replica using an optical phase-locking and sampling technique’. 1991, Topical Meeting on Picosecond Electronics and Optoelectronics, Salt Lake City, Utah, USA, paper WB2-1

HUNG, H.-L. A., LI, M. G., HUANG, s.-L. L., and LEE, c.-H.: ‘Character- ization of microwave integrated circuits using an optical phase- locking and sampling system’. 1991 Int. Microwave Symp., Boston, MA, USA

3

4

5

6 LI, M. G., CHAUCHARO, E. A., LEE, C. H., and HUNG, H.-L. A . : ‘hler-

7

8

INEXACT M A T C H ASSOCIATIVE M E M O R Y CELL

Indexinq terms: Memories. Parallel processing

time delay,lO psldlvl51or ‘C9. 3 Fig. 3 10.0 GHz microwaue signal probed by electro-optic sampling

0 experimental data

~ 10.0GHz sinusoid

can be synchronously probed electro-optically by the 1.3pm LD without offset, i.e. ,fm = N f i , in our scheme.

In summary, we have demonstrated electro-optic sampling of I 0 . 0 G H r optoelectronically phase-locked microwave signals using semiconductor laser diodes. One potential application of this technique is for the characterisation of MMICs at the wafer level.

A c k n o w l e d g m e n t : This work was partially supported by the National Science Council of the Republic of China under grant NSCSO-0417-E-009-05.

H.-H. W U 24rh June 1991

C.-S. CHANG

C.-L. PAN

Inst. of Electro-opt. Eng. and C t r . Jar Telecom. Res National Chiao Tung University

Hsinchu. Taiwan 300, Republic of China References

I VALOMANIS J. A . : ‘Electro-optic measurement techniques for picosecond materials, devices and integrated circuits: in MARCUS, R. B. (Ed.): ‘Measurements of high speed signal in solid state devices, semiconductors and semimetals’ (Academic Press, 19901, Vol. 28.

pp. 136219

A new associative memory cell is described and analysed using SPICEMI. The CMOS cell uses current summation to compute, in parallel, Hamming distances between the search key and each word in the memory. For 32 bit words, SPICE simulations of a 2pm process show a delay of 4ns/bit for Hamming distances less than three.

I n t r o d u c t i o n : The first uses of associative memories were in system architectures to improve the translation table lookup process in the cache memory.’ The improvement is the result of the parallelisation of an exact match of a search key t o all words stored in the translation buffer memory. An exact match, B bits in length, can be expressed as

i = 1

where S , is the value of the ith bit of the search key,

W;

1s the value of the ith bit of the word stored in the associative memory and 8 is the exclusive-OR operator. Many associative memories evaluate the contribution of each bit to the above product ( m a t c h ) by using a six transistor static memory and a pass transistor exclusive OR. The output of the exclusive O R controls an input to a B input N O R gate. This cell is shown in Fig. I . The area labelled N O R in Fig. 1 is not the entire B input NOR. In the memory, the output of the N O R gate ( m a t c h ) extends along the word axis of the memory and is terminated with either a clocked (dynamic gate) or resistive load (ratioed gate). If for example, a ratioed pullup completes the logic for m a t c h , m a t c h = 1 indicates that all B bits of the search key and the memory word are identical; this is an exact match. If one or more bits in the search key differ with the memory word, m a t c h will equal logic 0. In a memory of M words, the search key can be compared t o all the words in the memory simultaneously because every word in the memory will have its own m a t c h line. The two simple circuit techniques outlined provide two types of parallelism: bit parallelism from the extended NOR and word parallelism from the multiplicity of m a t c h lines. When compared to RAM, these orthogonal parallisations are the sources of improvement for the lookup process in cache memory design. Cache design and other