Bias Current Sources with Positive Temperature Coefficient: This section contains a number of ultra-low-power (e.g., nano-ampere) “Proportional to Absolute Temperature” (PTAT) current sources (IPTAT), which have a positive temperature coefficient (TC) and can be fabricated in standard digital CMOS. IPTAT current sources are fundamental building blocks, generally providing a lifeline for other analog circuits (e.g., amplifiers, voltage references, ADCs, DACs, etc.). As such, Ai Analog offers numerous proprietary IPTAT intellectual property (IP) cells tailored to the different needs of other analog circuits they serve. These needs include less dependence on PMOSFETs vs. NMOSFETs, low operating VDD vs. low voltage coefficient, PTAT loops coupled to VDD or VSS, etc. The IPTAT circuits also include a start-up and power-off feature. Some of the common traits of IPTAT circuits are summarized below.

The intellectual property (IP) cells are generally portable from trailing-edge to bleeding-edge CMOS.

• Tiny CMOS bias current cell with positive temperature coefficient (TC) operating in subthreshold with ultra-low current consumption (IDD).
• Large value but tiny active bias resistor (RA) keeps IDD ultra-low.
• IDD and IOUT absolute values are mostly a function of MOSFET mobility (µ), inherently more stable to help narrow IDD variation over fabrication process corners.
• Diverting most leakages (of RA and key FETs) to supplies to improve the temperature range.
• No clock, no switch-capacitor, and no related noise or injections into the substrate.
• Narrow variations over manufacturing processes are also due to IDD and IOUT being less sensitive to VTH.
• No passive resistors and no passive capacitors keep the area small and silicon cost low.
• IOUT can be calibrated or trimmed for TC.
• Programmable (pre- or post-silicon) IOUT that tracks IDD.