An Add-On Type Real-Time Jitter Tolerance Enhancer for Digital Communication Receivers An add-on type real-time jitter tolerance enhancer (JTE) is presented in this paper. The proposed JTE can improve high-frequency jitter tolerance (JTOL) by using a real-time phase alignment scheme. A mathematical analysis for an advanced bit error rate (BER) prediction method is also introduced. The proposed circuit is applicable to various types of receivers, such as referenceless receivers, receivers with a reference clock source, and source-synchronous receivers. The referenceless receiver with the proposed JTE achieved an out-of-band JTOL of 0.71 UIpp at 100 MHz with <10⁻¹² BER. This is 196% higher than a conventional receiver without the JTE. The source-synchronous receiver with the proposed JTE achieved 0.92 UIpp at 300 MHz with <10⁻¹² BER. Total core areas of the receiver and JTE are 0.19 and 0.07 mm² in a 0.13-μm CMOS process, respectively. The power consumption of the receiver is 38 mW at 5.4 Gbit/s, and the JTE dissipates 22 mW