The continued aggressive scaling of semiconductor devices has had detrimental effects on the performance of those devices as used in analog circuitry. Specifically, the maximum intrinsic gain (MIG) of the devices continues to degrade as the device channel lengths are reduced below 100 nm and beyond. MIG is shown to degrade from 21.6 dB in a 180 nm technology to 12.2 dB in a 65 nm technology despite the application of traditional design techniques including device size scaling and bias voltage increases. This reduction in MIG along with other process scaling effects significantly complicates the design of linear amplifiers in these technologies. This work proposes the use of positive feedback to compensate for MIG degradation in linear amplifier design in scaled technologies. Criteria for stable and process tolerant design are derived and examined in the context of amplifier models of varying degrees of complexity. This analysis defines an all-encompassing positive feedback design methodology for use in linear amplifier design of low-gain high-frequency amplifier design. Additionally, the effects of positive feedback are compared and contrasted to the effects of the commonly studied negative feedback design methodology. Finally, the methodology is applied to a differential amplifier stage in TSMC's 65 nm process using standard threshold voltage, thin oxide CMOS devices. These amplifiers were fabricated and tested to validate the positive feedback design methodology. Simulation shows that 98.4% of positive feedback amplifiers have improved gain over the baseline differential amplifier with an average improvement in gain of 10.3 dB. Silicon measurements of the amplifier gain show improvements of 17.1 dB on average. Similar to the application of negative feedback, gain improvement is achieved at the cost of frequency response. The gain-bandwidth product of the amplifier is reduced by an average of 18.4 GHz from 44.6 GHz. The circuitry required to implement this technique represent a meager 6% increase in silicon area from 460 μm2 to 488 μm2.
Library of Congress Subject Headings
Metal oxide semiconductors, Complementary--Design and construction; Nanoelectronics; Amplifiers (Electronics)--Design and construction
Department, Program, or Center
Microsystems Engineering (KGCOE)
Pude, Mark, "Circuit solutions to compensate for device degradation in analog design in scaled technologies" (2013). Thesis. Rochester Institute of Technology. Accessed from
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