A voltage and temperature stable threshold-voltage reference circuit

Abstract

An improved threshold-voltage reference (V(sub TR)) circuit operated at subthreshold current region has been presented and compared with a bandgap-voltage reference (V(sub BR)) circuit. MOSFET threshold voltage as reference source makes it possible to control output voltage V(sub TR) by substrate bias. Since drain voltage difference affects I-V characteristics even in subthreshold region, drain voltage equalization by adding an n-MOSFET improves voltage- and temperature-dependence of the V(sub BR)/V(sub TR) circuits. The circuits were fabricated by 1.2 micrometer n-well CMOS process. V(sub BR) approximately equal to 1.26 V and V(sub TR) approximately equal to 1.29 V were obtained for both circuits. The change of (V(sub BR)/V(sub TR)) for the supply voltage V(sub DD) = 5.0 +/- 1.0 V and T = - 60 to + 100 C was improved from (3.3/2.8) to (1.1/1.0) percent. V(sub TR) reference had a little larger fluctuation of output voltage at V(sub DD) = 5.0 V and T = + 20 C, but a little smaller V(sub DD) and T dependence. V(sub TR) was controlled from 1.29 to 1.71 V by the substrate bias voltage V(sub Sub) supplied to n-MOSFETs from 0.0 to - 2.0 V, and the change of V(sub TR) for V(sub DD) = 5.0 +/- 1.0 V and T = - 60 to + 100 C was further improved from 1.0 to 0.6 percent by V(sub Sub) supply.

MOSトランジスタのしきい値電圧を用いた基準電圧発生回路(V(sub TR))を提案した。サブ・スレッショールド電流領域の特性を利用し、従来のバンドギャップ型の基準電圧回路(V(sub BR))よりも、電源電圧(V(sub DD))および温度(T)依存性を改善している。また、基板バイアス(V(sub Sub))によってしきい値電圧を変化させることができるため、基準電圧出力も制御可能である。ドレイン電圧の不均衡に起因するサブ・スレッショールド電流の差を抑制するため、電圧補償用のn-MOSトランジスタを追加し、V(sub DD)、および温度依存性を改善した。提案した回路を1.2μmCMOSプロセスで試作した結果、V(sub BR)=1.26VおよびV(sub TR)=1.29Vの定電圧が得られた。V(sub DD)=5.0±1.0V、T=-60度C?+100度Cの範囲での出力(V(sub BR)/V(sub TR))の変動幅は、電圧補償用トランジスタによって、それぞれ、(3.3/2.8)％から(1.l/1.0)％へ減少できた。出力V(sub TR)はV(sub BR)に比べて、V(sub DD)=5.0V、T=+20度Cでのバラツキはやや大きいが、V(sub DD)および温度依存性は改善された。V(sub Sub)を0から-2.0Vに変えると、V(sub TR)を1.29から1.71Vへ変化させることができ、V(sub DD)=5.0±1.0V、T=-60度C?+100度CでのV(sub TR)の変動幅を、1.0から0.6％へ抑制することができた。