TABLE OF CONTENTS As we learned from the previous chapter, some of the most accurate BJT-based current sources that the designer can create at the circuit board level use precision matched-pairs and quads. These are available from Analog Devices, National Semiconductor, and second-source specialists Linear Integrated Systems. Precision matched monolithic BJT pairs and quads represent the highest quality and precision available in a silicon transistor. All three manufacturers make NPN matched-pairs. Analog Devices and Linear Integrated Systems also offer PNP matched-pairs. Additionally, Analog Devices makes a quad NPN device. Overall, Linear Integrated Systems provides a wider range of different package options than any other manufacturer. Some of the company's matched-pairs are super-gain transistors (not Darlingtons), with h FEs upward of 1000. Many of the BJT circuits shown in Chapter 4 can be optimized by using any of these high-performance matched-pairs and quads.
What makes precision matched-pairs so special? Unlike dual transistors or multiple transistors that are packaged as an array, matched-pairs have specifications far exceeding those of high-performance discretes or a typical multitransistor array. Precision matched-pairs rely on a specially designed paralleled transistor structure (not unlike today's power MOSFET structure, which also uses many paralleled cells in order to create one single FET device with very low on-resistance). With the precision matched-pair/quad BJT, a similar technique dramatically reduces the base-emitter bulk resistance to levels typically less than an ohm (this resistance is often more than 50 ? in a regular discrete transistor). They also receive special processing,...
