An evaluation of MOS interface-trap charge pump as an ultralow constant-current generator

Abstract

In this work, we explore the MOS interface-trap charge-pump as an ultralow constant-current generator for analog CMOS applications. Charge pumping techniques in general are more suitable than conventional continuous-time techniques for ultralow current generation because the linear controllability of current by frequency is maintained regardless of the level of current. An interface-trap pump has the same property but the minimum charge it puts out per cycle is at least two orders of magnitude smaller than that of a switched-capacitor charge pump. This helps generate the same current more accurately at a much higher frequency with a much smaller filter capacitance. The paper presents a simplified model of the terminal characteristics of the interface-trap pump and an evaluation of its performance as a stand-alone current generator. Cascoding and complementary pumping are introduced as measures of performance improvement. Temperature sensitivity, pulse feedthrough, controllability, matching, reliability, and trimming issues are addressed. Transconductor circuits built with the charge pump are presented and experimentally evaluated.

A high-sensitive digital photosensor using MOS interface-trap charge pumping

“…The calculated D it with a typical energy range ∆E ≈ 0.5 eV is 1.2 × 10 10 cm −2 , which is close to the previously reported value [8].…”

“…We make use of MOS ITCP to control the amount of Q inj . The ultra-low current sources using this phenomenon have been reported [7,8].…”

“…Assuming typical values, we can get an extremely small injection charge Q ss ≈ 3.5 aC (22 electrons per cycle) with the gate area of 0.5 µm × 2.5 µm [8]. …”

A 3.3V CMOS Charge-Pumping Offset-Compensated Optical Charge-Mixer with 3% Phase Accuracy

“…It exploits the Charge Pumping phenomenon, which was discovered in 1969 [2] and is extensively used as a powerful analysis method for evaluate and quantify the degradation of MOS transistors [3][4][5]. Recently, charge pumping has been used as frequency-controlled ultra-low current generator for analog CMOS applications [6] and as charge-mixer [7]. This technique is extremely linear with respect to the clock frequency and can pump charge packets per cycle two order of magnitude smaller than those of a switched-capacitor charge pump.…”

Compact sub-hertz ota-c filter design with interface-trap charge pump

“…All of these measures inevitably add to the silicon real estate occupied by the filter and increase the leakage floor and noise. This paper explores the recently proposed MOSFET interface-trap charge-pumping (ITCP) current generator and transconductor circuits as a basis for ultralow frequency OTA-C filter design [10]. These very compact circuits offer not only the lowest possible transconductance as determined by leakage currents, but also more than two orders of magnitude range for linear transconductance control.…”