The voltage offset error of the amplifier across these external conditions (such as temperature, operating voltage, etc.) must be carefully considered, as this behavior could directly impact the performance of the overall design. Therefore, changes in external operating conditions will adversely affect the accuracy of the amplifier. Like non-volatile memory fuses, laser trimming is done once during the time of manufacture, with no option to retrim the device. Such assembly-related changes cannot be accounted for when trimming and, hence, will add to the error of the amplifier. The processes of sawing the wafer into individual die, placing the die in a package, and bonding the die to the packaged pins can all cause mechanical stress on the wafer that will negatively affect the overall accuracy of the device. However, laser trimming cannot be done within a packaged device, and can only happen at the wafer level.
Another advantage of laser trimming thin-film resistors is that these resistors are inherently very stable over temperature, adding to the overall accuracy of the amplifier across a wide temperature range.
The accuracy of this approach can be relatively high, since the trimming process is continuous (as opposed to involving discrete steps, as in EPROM trimming). This process involves using a laser to adjust the resistance value of thin-film resistors located within the silicon wafer. Also, like a general-purpose amplifier, this architecture will be sensitive to environmental conditions such as temperature, as well as changes in common mode or operating voltage.Īnother method often used to increase the accuracy of an op amp is laser trimming. Hence, the EPROM-trimmed devices can be somewhat limited in terms of ultra-small packaging. However, the EPROM fuses take up a certain amount of silicon area. The amplifier is trimmed by the manufacturer and does not require the customer to do anything. The other advantage of this architecture is that it does not require any customer inputs. Since the trimming is done post-assembly, any assembly-related offsets can be corrected. In many cases, this process is done in-package during the final test of the device, and is a very cost-effective way to provide an amplifier with low initial offset voltage. This method implements nonvolatile EPROM fuses to correct the input offset voltage of the amplifier. The first architecture uses nonvolatile memory. Depending on the application, these external conditions may determine the best amplifier architecture for your design. These environmental conditions include changes in common-mode voltage, operating voltage, output voltage, temperature, and even time. When discussing precision op amps, it is important to not only consider the initial input offset voltage, but also the behavior of this error voltage across various environmental conditions. A “precision” amplifier implements some form of input offset correction, typically by using one of the architectures discussed here. This error voltage can vary from microvolts up to millivolts, and is highly dependent on how well matched the input transistors are. As the name implies, this specification is the amplifier’s voltage difference between the inverting and non-inverting inputs. This term typically relates to the input offset voltage of the amplifier. This article will explain the fundamentals of these various architectures, and explore the benefits and shortcomings of each.īefore discussing the various op-amp architectures, it is important to clarify what is meant by the term “precision” op amp. Multiple architectures exist, including the use of nonvolatile memory, laser trimming, auto-zeroing and even on-chip calibration circuitry. However, today’s system designer has many options when it comes to low-offset op amps. These devices can simplify system design and/or manufacturing by eliminating the need for a system calibration, either during manufacturing or while the product is in the field. Finding the right architecture for your designĪs technological advances continue to drive down the prices of ICs, more and more system designers are opting for higher-precision operational amplifiers.