TABLE OF CONTENTS Barrie Gilbert
Few readers of this book will need to be introduced to the concept of the current mirror; it has become a familiar icon of modern analog design. Accordingly, we will deal only briefly with the well-established foundations of the subject, already adequately presented in many excellent texts[1], and concentrate instead on developments of the basic current-mirror forms, having properties suited to special, though not uncommon, applications. Some of these developments have been included only to illustrate the wide variety of possibilities, and may not have any immediate practical value; this is true of the high-ratio forms presented in Section 6.5.2.
In principle, the basic function could have been realized before the advent of the bipolar junction transistor (BJT), but the unique properties of this device opened the door to efficient and eminently practical forms of mirrors, now to be found in a large proportion of analog ICs (and in many digital ones, too). The design approach used here is based strongly on the translinear view of the BJT. In many cases, this will mean the invocation of strict-TL forms of which the classical current mirror is the simplest possible example. Just as probable, however, will be a strong dependence on the basic translinearity of the BJT, that is, the predictable behavior of many special-purpose current mirrors will frequently hinge on the unique relationship between collector current, I C, and base-emitter voltage, V BE; they are "TN" circuits, although not...
