Methods and apparatus for trimming electrical devices

#The present invention relates generally to electronic devices and more particularly to improved trim circuitry and methods for trimming electronic devices.

#Trim circuits are found in many types of electrical devices where a voltage, current, or other operational parameter of a device needs to be adjusted, either during or following manufacturing. Such trim circuitry typically provides a resistance between two nodes in an integrated circuit device, which may be selectively removed, in whole or in part, from the circuit upon application of voltages or currents to trim pads in the device. Trim circuits often employ zener diodes connected in parallel with the resistor to be removed, where the application of an appropriate trim voltage across the diode terminals short-circuits the resistor, sometimes referred to as “blowing” the diode.

#In other trim circuits, open-circuits may be selectively created so as to adjust the device performance. In this instance, fuses are often formed in the trim circuit, which can be selectively open circuited by conducting a fuse trim current through the fuse, sometimes referred to as “blowing” the fuse. Such trim circuits, including fuse types and diode types, find application in a wide variety of electrical devices. For instance, trim circuits are often employed in voltage reference or regulator devices wherein one or more reference voltages generated by the device are adjusted during the manufacturing process, such as prior to packaging individual devices.

#FIG. 1A is a schematic diagram illustrating a conventional diode type trim cell having a resistor and a zener diode connected in parallel;

#FIG. 1B is a schematic diagram illustrating the trim cell of FIG. 1A after the diode has been sacrificially destroyed to short the resistor;

#FIG. 1C is a partial top elevation view illustrating the trim cell of FIGS. 1A and 1B;

#The present invention will now be described with reference to the attached drawings, wherein like reference numerals are used to refer to like elements throughout. The invention relates to methods and apparatus for trimming electrical devices. Several exemplary implementations of the various aspects of the invention are illustrated and described below, including single-bit and multi-bit trim circuits and trim cells thereof. However, it will be appreciated that the illustrated implementations are exemplary in nature and that the invention and the appended claims are not limited to the examples specifically illustrated and described herein.

#Referring initially to FIGS. 2A and 2B, one implementation of the invention is illustrated schematically, wherein a trim circuit 102 comprises a resistor 104 and a zener diode 106, with the resistor 104 initially providing an electrical resistance between first and second pads A and B at first and second ends thereof. FIG. 2A illustrates the initial condition of the circuit 102 and FIG. 2B illustrates a final condition of the circuit 102 following destruction of the diode 106 to short-circuit the resistor 104.

#The pads A and B may be connected to first and second circuit nodes in an electrical device (not shown) of which the trim circuit 102 is a part, wherein adjustment in the electrical resistance between the nodes may be desired. For example, the trim circuit 102 and other trim circuits and cells illustrated and described hereinafter may be employed for selective removal of resistance between two circuit nodes to provide adjustment of an operating parameter associated with such electrical devices. Thus, for instance, a reference voltage may be advantageously adjusted in a voltage regulator device using the circuits and methods of the present invention by selective removal of all or a portion of electrical resistance between two nodes in the device.