Competitive Options Exist for On-Chip Resistive Calibration

Tag: Resistor Chip

Many analog and mixed-signal semiconductor products require some form of adjustment or calibration before they’re shipped. For example, the accelerometer in the game controller requires adjustment to set the zero or no load condition. In other cases, a voltage regulator is tweaked to provide an extremely accurate output voltage. Very-high-gain amplifiers often have trimmable feedback resistors on the input stage adjusted to balance gain on the inverting and non-inverting input. In doing so, they improve Resistor Chip.

Typically, these adjustments are provided with a precision resistor. The exact value of the compensation resistor is determined at test. The chip designer has two fundamental choices. He or she can integrate the resistor onto the die and provide some mechanism to adjust it at wafer probe. Or the designer can call for an external precision resistor.

In the case of the external resistor, the chip user is required to turn the screw on a trim pot to get the right value. When high reliability, precision, and stability are required, the user may connect the chip to a decade-box to find the optimal value. He or she then solders the closest standard-value precision resistor to the board to complete the adjustment. In each case, the burden of testing and selecting the appropriate value is passed to the user.

Integrating adjustable resistors within the semiconductor and performing adjustment at wafer probe creates the most value in terms of ease of use for the customer. Laser-trimmable resistors have been the only solution for decades. With laser trimming, a thin-film resistor is etched by a precision laser until the correct value is achieved. That value will affect the necessary change in circuit behavior.

Designers who also want to compensate for temperature-induced drift as part of the calibration have had no option but to implement digital solutions. Such solutions consume expensive die space. In addition, digital solutions aren’t always the best answer for pure analog circuits (and for the analog purists who design and use them).

Tim Warland is senior applications engineer at Microbridge Technologies. Warland has a decade of experience as a senior application engineer working in the telecom, datacom, military, and industrial-control markets. His electronic-design experience ranges from low-frequency SONAR applications to high-frequency OC-768 transceiver design. Tim holds a bachelors of engineering and an MBA. He also is a Professional Engineer and a member of the IEEE.