I. Vazquez-Alvarez

A CMOS Low-Voltage Super Follower Using Quasi-Floating Gate Techniques

A quasi-floating gate (QFG) “super-follower” is presented. The high resistance used by the QFG transistor is constructed by two diodes connected back-to-back, leading to a simple-, temperature-stable- and small-area solution. Expressions for the behavior of the follower are introduced and verified by circuit simulations in LTSPICE using 0.5μm CMOS process models, which show an improved performance of the proposed circuit with respect to the original super-follower. To prove the principle, a test cell was fabricated in the same 0.5μm CMOS technology and characterized. Measurement results show a gain-bandwidth product of 10MHz and power consumption of 120μW with a 1.5V single supply.

A Low-Complexity Delta-Sigma Modulator (

In recent years, inverter-based sigma-delta (ΔΣ) modulators have received great attention as a suitable approach for the design of low-voltage, low-power, switched-capacitor ΔΣ. This method uses digital inverters as the active elements to construct the integrators in the ΔΣ loop. In some applications, a reduced silicon area implementation is an important constraint; this demands the use of only one inverter in the integrator. This paper proposes to use the common-source amplifier as the building block to achieve the operation of integration instead of the digital inverter. This leads to the operation of the amplifier in strong inversion combined with low-voltage supply and compact chip area. The idea was confirmed with a prototype fabricated in a 0.5-μm CMOS technology available through Metal Oxide Semiconductor Implementation Service (MOSIS). Using 250 kHz of sampling frequency, measurement results show a signal-to-noise and distortion ratio of 70 dB over a bandwidth of 125 Hz. The circuit consumes 38 μW when powered from a single 1.5-V supply voltage and uses 200 × 260 μm of active area. Circuit simulations in SPICE show the potential of this method to work with 450 mV of power supply in a 50-nm CMOS technology.