Transistor array

Transistor arrays consist of two or more transistors on a common <a href="/facts/Wafer_(electronics)/lCBJAoUL">substrate</a>. Unlike more highly <a href="/facts/Integrated_circuits/fjn6vg7C">integrated circuits</a>, the transistors can be used individually like discrete transistors. That is, the transistors in the array are not connected to each other to implement a specific function. Transistor arrays can consist of <a href="/facts/Bipolar_junction_transistor/9BMcGv5Q">bipolar junction transistors</a> or <a href="/facts/Field-effect_transistor/TerYC6Nz">field-effect transistors</a>. There are three main motivations for combining several transistors on one chip and in one package:

<ol><li>to ensure closely matching parameters between the transistors (which is almost guaranteed when the transistors on one chip are manufactured simultaneously and subject to identical manufacturing process variations)</li>
<li>to ensure a closely matching thermal drift of parameters between the transistors (which is achieved by having the transistors on a common substrate, and in extremely close proximity)</li>
<li>to save <a href="/facts/Circuit_board/muSR2p43">circuit board</a> space and to reduce board production cost (only one component needs to be populated instead of several)</li></ol>
The matching parameters and thermal drift are crucial for various <a href="/facts/Analogue_circuit/Bnlnfwwv">analogue circuits</a> such as <a href="/facts/Differential_amplifier/0MWj8eCR">differential amplifiers</a>, <a href="/facts/Current_mirror/cUa0QNDQ">current mirrors</a>, and <a href="/facts/Log_amplifier/ECWeHI2k">log amplifiers</a>.
The reduction in circuit board area is particularly significant for digital circuits where several switching transistors are combined in one package. Often the transistors here are <a href="/facts/Darlington_transistor/2QGqjsgP">Darlington pairs</a> with a common emitter and <a href="/facts/Flyback_diode/qzV5mPo3">flyback diodes</a>, e.g. <a href="/facts/ULN2003A/DTylQxmE">ULN2003A</a>. While this stretches the above definition of a transistor array somewhat, the term is still commonly applied.
A peculiarity of transistor arrays is that the substrate is often available as a separate pin (labelled substrate, bulk, or ground). Care is required when connecting the substrate in order to maintain isolation between the transistors in the array as <a href="/facts/P%25E2%2580%2593n_junction_isolation/6VcmMwQa">p–n junction isolation</a> is usually used. For instance, for an array of NPN transistors, the substrate must be connected to the most negative voltage in the circuit.

Transistor array open-in-new

Transistor array