PTAT CMOS current sources mismatch over temperature

Proportional to Absolute Temperature (PTAT) CMOS current sources are widely used in temperature sensors, bandgap references, and other temperature-compensating circuits. Most of these applications strongly rely on the accuracy of a current ratio m established with a set of 1+m PTAT current sources. However, a PTAT CMOS current source has a temperature-dependent bias point, which in turn, has a well-known effect on the mismatch of CMOS current sources. This paper analyzes the mismatching properties of PTAT current sources due to variation of the current-sources bias point (g_m/I_DS) with temperature, from -55°C to 125°C. After the analysis, the paper shows measurements of a precision temperature sensor without mismatch compensation to corroborate the analysis developed.