Substrate coupling in a high-gain 30-Gb/s SiGe amplifier-modeling, suppression, and measurement

For demonstrating substrate coupling in high-gain broadband amplifiers, a limiting differential transimpedance amplifier has been developed and fabricated in a SiGe bipolar technology. It operates up to 30 Gb/s and stands out for a maximum (nonlinear) transimpedance in the limiting mode of 25 kΩ, resulting in a gain × speed product as high as 750 kΩ·Gb/s. This record value could be achieved by applying several techniques for suppression of noise coupling simultaneously. The effectiveness of each technique was verified experimentally by measuring the output eye diagrams of different mounted amplifier versions. The high accuracy potential of the substrate modeling tools applied for optimizing the amplifier design has been demonstrated separately by measurements on special (mounted) test structures up to 40 GHz. These investigations also showed the strong degradation of shielding measures by bond inductances with increasing frequency.