Circuits and methods to produce a VPTAT and/or a bandgap voltage with low-glitch preconditioning

Provided herein are circuits and methods to generate a voltage proportional to absolute temperature (VPTAT) and/or a bandgap voltage output (VGO) with low 1/f noise. A first base-emitter voltage branch is used to produce a first base-emitter voltage (VBE1). A second base-emitter voltage branch is used to produce a second base-emitter voltage (VBE2). The circuit also includes a first current preconditioning branch and/or a second current preconditioning branch. The VPTAT is produced based on VBE1 and VBE2. A CTAT branch can be used to generate a voltage complimentary to absolute temperature (VCTAT), which can be added to VPTAT to produce VGO. Which transistors are in the first base-emitter voltage branch, the second base-emitter voltage branch, the first current preconditioning branch, the second current pre-conditioning branch, and the CTAT branch changes over time. The current preconditioning branches are used to appropriately precondition transistors with an appropriate amount of current as they are switched into and out of the various other circuit branches.