A compact, high linearity 40GS/s track-and-hold amplifier in 90nm SiGe technology

The design of low distortion, high speed transceivers requires high performance Track and Hold Amplifier (THA) front ends to Analog to Digital Converters. This paper reports the design and characterization of a highly linear THA fabricated in 90nm SiGe Heterojunction Bipolar Transistor technology with Effective Number of Bits>4.9. Improved linearity is achieved through feed-through cancelation techniques, peak cutoff frequency biasing and a differential layout. The circuit is tested over a wide input frequency range of 1–19GHz with a fixed clock frequency of 40GS/s. It exhibits Spurious Free Dynamic Range as high as 78dB, Total Harmonic Distortion less than −31dB and peak Input-referred 3rd order Intercept Point of 11.1dBm. The circuit has an input-referred 1dB compression point of 6dBm and consumes 560mW of power while occupying 0.03mm² of active die area. The SFDR3 and THD3 performance is better than similar circuits published in Silicon, and comparable to InP circuits, which consume more DC power. These results are promising for future designs of fully integrated ultra high speed transceivers in Silicon technologies.