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Enhanced folded source-coupled logic technique for low-voltage mixed-signal integrated circuits

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2 Author(s)
J. Kundan ; Intel Penang VLSI Design Center, Malaysia ; S. M. R. Hasan

The advantages of CMOS differential-stack current-mode logic techniques together with the load-driving capability, switching speed, and noise immunity of bipolar devices has been exploited to develop a novel enhanced folded source coupled logic (FSCL) technique. A pair of quiet low-impedance push-pull load steering emitter followers (EF's) are implemented at the mutually complementary outputs of the CMOS FSCL (CFSCL) gate to obtain the EF2SCL gate structure. This modification considerably improves the performance of the gate at low supply voltages for a mixed-mode environment (e.g., ΣΔ data converters in digital audio, video, and radio frequency applications) without the cost of substantial power-supply spikes. Thorough current steering and dynamic-charge storage analysis at 100 MHz, using a 3.3-V supply voltage and BSIM process parameters was performed to evaluate the performance enhancement achievable by the EF2SCL technique. A 4-bit carry-lookahead with carry skip was achieved in 2 ns using a single EF2SCL logic gate, compared to 9 ns for a CFSCL gate. In addition, the deterioration of the voltage-swing (and hence the noise margin) with power-supply scaling and increased differential logic input stack-size is considerably more pronounced in a CFSCL gate compared to an EF2SCL gate. EF2SCL thus permits logic implementation using fewer stages compared to CFSCL, and hence reduces delay latency in a pipelined system. A tiny chip using MOSIS Orbit 2-μm n-well analog CMOS process (which provides a p-base diffusion layer for low-cost n-p-n device option) was used for the experimental verification

Published in:

IEEE Transactions on Circuits and Systems II: Analog and Digital Signal Processing  (Volume:47 ,  Issue: 8 )