Optically clocked switched-emitter-follower THA in a photonic SiGe BiCMOS technology

Abstract

In this paper a novel opto-electronic Track-and-Hold Amplifier (OE-THA) is presented. The OE-THA can be used as a sampler in a photonic analog-to-digital-converter (ADC). It is fabricated in a silicon photonic 250 nm SiGe BiCMOS technology to allow for monolithic integration of photonic and electronic components. The OE-THA chip exhibits a small signal bandwidth of over 65 GHz, a total harmonic distortion below −34 dB up to 75 GHz and a signal-to-noise and distortion ratio (SINAD) of over 35 dB (5.5 effective bits, ENOB) up to 45 GHz. The measured resolution bandwidth products result in a corresponding equivalent jitter of below 80 fs rms from 20 to 70 GHz. The best equivalent jitter is achieved at 41 GHz with a value of 55.8 fs rms. This is enabled by using a low-jitter optical pulse train, generated by a Mode-Locked-Laser (MLL), as an optical sampling clock. The circuit integrates all optical and electronic components besides the MLL. It draws 110 mA operated from a supply voltage of −4.6 V and occupies a silicon area of only 0.59 mm2.

Optically Enabled ADCs and Application to Optical Communications

“…Transient responses are reported in [20]. Here, we show measurements recorded by connecting the electrical output to a spectrum analyzer set to a 1 kHz resolution bandwidth (RBW).…”

“…However, it is also possible that the corresponding reduction of peak power in the 100 mW range (on chip) was instrumental in reducing two-photon absorption in silicon waveguides and preventing saturation effects in germanium PDs or in the following circuitry. Indeed, OE switching of the OE-THA was experimentally observed up to an 18 GHz switching rate utilizing a continuous wave laser modulated with a sine wave by an external MZM, as limited by the cutoff frequency of the modulator [20]. Simulations indicate that switching should be supported up to 30 GHz with the current circuit, so that 4 interleaved stages should be able to reach close to the 130 GS/s sampling rate required to make full use of the analog bandwidth.…”

“…Alternatively, the MLL pulse train can first be converted into the electrical domain to supply a low jitter clock signal to an electrical circuit [19], [20]. Both techniques allow leveraging the low jitter afforded by certain classes of MLLs [15], as opposed to combs generated by electro-optic transduction of radio-frequency (RF) pulse trains [21] that are subject to the jitter of the electric source.…”

“…The opto-electronic (OE) circuit and its performance are described in this section. The interested reader will find a more detailed circuit analysis in [20].…”

Femtosecond-precision electronic clock distribution in CMOS chips by injecting frequency comb-extracted photocurrent pulses

“…For this reason, they have been actively used for precise timing applications, including synchronization of large-scale X-ray free-electron lasers 13 , high-speed photonic analogue-to-digital converters (ADCs) 14 and photonics-based radars 15 , to name a few. Naturally, utilizing ultralow-jitter optical pulses in electronic or electronic-photonic chips has also been actively investigated 16 – 23 . For the on-chip clocking, an early-stage pioneering experimental study employed ultrashort optical pulses generated from an 80 MHz mode-locked Ti:sapphire laser to inject a local clock signal to a four-stage flip-flop with 5.9-ps timing jitter 16 , and later to a multiplexer down to 0.93-ps jitter 24 .…”