A differential 70 GSa/s track-and-hold amplifier has been designed and fabricated in a 320 GHz-f T InP double heterojunction bipolar transistor process. Measurements show a 51 GHz small-signal bandwidth with an S 11 parameter lower than −15 dB up to 56 GHz. The transient operation is verified up to 70 GSa/s. 60 GSa/s spectral measurements give total harmonic distortion <−46 dB up to 7 GHz and <−37 dB over the whole measurement range.Introduction: Most high sampling frequency and linear ADCs architectures often use one or several track-and-hold amplifiers (THAs) as input interface. ADC performances are based on those of the THA which is the main block. These THA circuits need a large bandwidth, a good linearity, a high sampling rate with an excellent isolation and low losses during hold mode. High sampling and large bandwidth THAs are fabricated in InP [1,2] or SiGe [3,4] technologies. These THAs with 40 GSa/s [3] and 50 GSa/s [2, 4] sampling rate are based on a switched emitter follower (SEF) structure while the circuit presented in [1] uses base-collector diodes. These circuits show small-signal bandwidths between 16 and 50 GHz.In this Letter we present a differential 70 GSa/s THA circuit fabricated in InP-DHBT with 50 GHz small-signal bandwidth. 70 GSa/s transient measurements are presented.

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Performances of two switched emitter follower structures for large bandwidth applications have been optimised, compared, implemented and measured. These circuits have been fabricated with a 320 GHz-F T InP double heterojunction bipolar transistor process. Measurements in track mode show a small-signal bandwidth over 65 GHz for one structure and over 50 GHz for the other. Track mode SFDR measured for 500 mV PP up to 15 GHz signal input is greater than 45 dBc.Introduction: High sampling frequency and linear ADCs are of interest for several applications such as the optical, wireless and military communication industries. Recent ADCs most often use track and hold amplifiers (THAs) input interface. These THAs need a large bandwidth, a good linearity, a high sampling rate with an excellent isolation and low losses during hold mode. The switched emitter follower (SEF), which is the main block of the THA, defines these performances.A 40 GHz small-signal-bandwidth two-stage-InP-SEF with an isolation of 25 dB and a 42 GHz small-signal-bandwidth SiGe-THA based on a classic SEF were proposed in [1] and [2], respectively. Different SEF architectures used in a 16 GHz small-signal-bandwidth SiGe THA were reported in [3].In this Letter we present two different large bandwidth InP-DHBT SEF circuits: a two-stage SEF structure and a single-stage SEF structure followed by an emitter follower (EF). Analysis of hold mode isolation is followed by comparison of measurements and simulation results of both circuits in track and hold mode.