A gate leakage current based nano-ampere current reference generator using a dual threshold voltage 6-T voltage reference

Abstract

To realize nano-ampere current reference generator, a tunable 1.34 nA current reference generator is proposed by applying the reference voltage to a PMOSFET achieving low temperature coefficients (TCs). Unlike the conventional resistors occupying large die area, the area was significantly reduced by using the gate-leakage PMOSFET. Furthermore, the area-efficient reference voltage based on MOSFETs operated at subthreshold rather than the accurate but power- and area-hungry bandgap reference was utilized. To cope with process variations, the reference current can be trimmed by four switches and is easy to be replicated. The proposed current generator was designed and fabricated on the die area of 0.0175 mm^2 using 90 nm CMOS technology. The measured TC of the 308 mV voltage reference is 124 ppm/°C and the measured TC of the 1.34 nA current reference is 394 ppm/°C from 0°C to 120°C at a supply voltage of 0.75V.

A 1.58 nJ/conversion temperature-to-digital converter with low power variations

“…The reference voltage (V ref ) generator adopts a 6-Transistor (6T) structure 28,29) composed of native and high threshold-voltage NMOSFETs, as depicted in Fig. 2.…”

“…The temperature-insensitive resistors R1 and R2 were implemented using the gate leakage characteristics of the low threshold voltage (LVT) PMOSFETs. 28,30) The reasons to use LVT PMOSFETs are due to their small temperature coefficients. 30)…”

An area-efficient sub-10 nW temperature-to-digital converter for thermopile temperature sensors

“…A reference voltage is required in the current generators. The reference voltage circuit operated in subthreshold composed of six transistors (6T) 30) as shown in Fig. 3(a) is adopted rather than two transistors (2T) 31) as shown in Fig.…”

“…The reference voltage (V ref ) has been formulated in Eq. (1), 30) in which the first term provides the negative TC and the second term produces the positive TC, where V th5 , V th6 are the threshold voltages of M 5 , M 6 , and V T is the thermal voltage. The nearly zero-TC of the V ref can be achieved by the appropriate ratio of W 5 L 6 /W 6 L 5 .…”

“…4 generate currents I 1 and I 2 in the order of pA, which can be achieved using the gate-leakage characteristics of MOS transistors. 30,32) Here, the low threshold (LVT) PMOS Fig. 1.…”