A Chopping-Free Single-Trim Bandgap Reference Using Amplifier With PTAT Offset

This article presents a chopping-free single-trim bandgap reference with an amplifier proportional-to-absolute-temperature (PTAT) offset. This amplifier PTAT offset is helpful for improving the BGR accuracy. Unlike the classic differential amplifiers, whose input-referred offset is usually non-PTAT, the proposed amplifier realizes a PTAT offset through controlling the current of a BJT-based structure. Similar to other PTAT error sources in a bandgap reference, this PTAT offset can be eliminated easily through a single room-temperature trim at the reference voltage. This makes the proposed circuit very simple and highly accurate, since it eliminates the need of complicated amplifier-offset cancellation techniques, such as chopping or autozeroing, that are usually used in prior single-trim bandgap reference circuits. It also eliminates the high-frequency ripple at the reference output, due to the no need of chopping. Besides the proposed structure, this article also presents a new technique to generate the amplifier bias current using only a tail resistor. Since a complicated biasing circuit is no longer needed, the proposed circuit is further simplified. Implemented in a 180-nm BCD process, the temperature coefficient (TC) is 3–8 ppm/^∘C at -55 ^∘C~125 ^∘C after a single trim at the room temperature, the output noise is only 1.5 μV_rms at 0.1–10 Hz, the current consumption is 590 μA, and the active area is 0.55 mm². According to the best of our knowledge, this is the first ever single-trim bandgap reference with no need of chopping or autozeroing.