Abstract
This paper presents a sub-threshold differential CMOS Schmitt trigger with tunable hysteresis, which can be used to enhance the noise immunity of low-power electronic systems. By exploiting the body bias technique to the positive feedback transistors, the hysteresis of the proposed Schmitt trigger is generated, and it can be adjusted by the applied bias voltage to the bulk terminal of the utilized PMOS transistors. The principle of operation and the main formulas of the proposed circuit are discussed. The circuit is designed in a 0.18-μm standard CMOS process with a 0.6 V power supply. Post-layout simulation results show that the hysteresis width of the Schmitt trigger can be adjusted from 45.5 mV to 162 mV where the ratio of the hysteresis width variation to supply voltage is 19.4%. This circuit consumes 10.52 × 7.91 μm2 of silicon area, and its power consumption is only 1.38 µW, which makes it a suitable candidate for low-power applications such as portable electronic, biomedical, and bio-implantable systems.
Highlights
As the electronics world is heading toward the future, electronic devices require longer lifetime batteries
A differential Schmitt trigger with adjustable hysteresis and transistors that are biased in the sub-threshold region is proposed. Hysteresis of this circuit is created by positive feedback and can be controlled by the body bias technique
By applying the body bias technique to the positive feedback transistors, no additional element is required to equip the circuit with hysteresis control capability
Summary
As the electronics world is heading toward the future, electronic devices require longer lifetime batteries. Circuits which operate in the sub-threshold region face some limitations such as poor frequency response and poor linearity [2] In general, these circuits are meant for low-frequency and low-current applications such as biomedical and biotelemetry devices and are not suitable for medium power applications [3,4]. Hysteresis of a Schmitt trigger is directly affected by process variations and transistor mismatches This issue is more problematic in applications where the level of noise and disturbances is not predictable [8]. A differential Schmitt trigger with adjustable hysteresis and transistors that are biased in the sub-threshold region is proposed Hysteresis of this circuit is created by positive feedback and can be controlled by the body bias technique. By applying the body bias technique to the positive feedback transistors, no additional element is required to equip the circuit with hysteresis control capability.
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