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A class AB CMOS current mirror with dynamic cascode biasing is presented. Measurement results show a wider input range and a linearity improvement of more than 23 dB with respect to the use of conventional biasing. The proposed current mirror, fabricated in a 0.5 mm CMOS technology, is able to operate with a supply voltage of 1.2 V and a quiescent power consumption of only 36 mW.
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Introduction: In modern analogue circuit design, current mirrors are one of the most utilised building blocks. They are used to replicate and distribute bias currents and as basic elements of current conveyors, voltagecurrent converters, filters, amplifiers etc. [1]. Relevant performance parameters of current mirrors in these applications include linearity, power consumption, minimum supply voltage required, input and output resistance.
To reduce static power consumption of a circuit without degrading dynamic performance, class AB topologies are preferred. However, conventional class AB topologies [2-4] add circuit complexity and usually increase the required supply voltage. In [5] a current mirror was presented able to achieve class AB operation using quasi-floating-gate (QFG) transistors [6] without penalty in terms of supply voltage, performance or circuit complexity. In this Letter, a new current mirror which uses QFG techniques to achieve both class AB operation and dynamic biasing of cascode transistors is proposed. Measurements show better linearity and wider input range than the class AB mirror in [5].
Proposed circuit: Fig. 1a shows the class AB cascode current mirror proposed in [5] in its simplest form (without feedback amplifier). Under static conditions, it is equivalent to a typical class A current mirror since Cbat is an open circuit in DC. While in a standard class A current mirror MN1-MN2 transistors form the current mirror and MP1-MP2 provide the DC bias current, in the circuit of Fig. 1a under dynamic conditions QFG transistors MP1-MP2 are dynamic current sources. If Iin becomes negative (positive) the current through MN1...