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Improved Low-Power Band-Gap Reference and Temperature Sensor Circuit and Method for Calibrating Same Disclosure Number: IPCOM000202453D
Publication Date: 2010-Dec-15
Document File: 6 page(s) / 185K

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Disclosed is a method to improve both the voltage reference circuit and the calibration of the same by removing the variations due to process, supply voltage, and mismatch. The method includes the conversion of the parallel current mirror/resistor structure to a series structure with a single current mirror.

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This is the abbreviated version, containing approximately 35% of the total text.

Page 01 of 6

Improved Low-Power Band-Gap Reference and Temperature Sensor Circuit and Method for Calibrating Same

The need for an accurate, temperature- and power supply-independent voltage reference circuit is ubiquitous in modern analog and mixed-signal integrated circuit (IC) design. In response to this need, the industry has developed a number of simple, small, and power-efficient circuits known as band-gap references. [1] These circuits are fashioned in bipolar and complementary metal-oxide semiconductor (CMOS) processing technologies and are in wide use in the integrated circuit industry. Like many reference generating circuit s , this circuit creates a temperature independent quantity (current or voltage) by mixing together weighted sub-quantities having opposite temperature coefficients. Supply independence is typically achieved by implementing a self-biasing circuit in combination with a startup circuit to guarantee that the self-biasing circuit will come out of the zero current/voltage state when a supply voltage is applied.

The increasingly common need with integrated circuits is for circuits to be capable of sensing the temperature on the IC at the point at which the circuit is instantiated. The accuracy requirements from such circuits vary widely; some applications require accuracy approaching 1 C or better; others are simply used to provide a coarse indication of the zone (out of several possible) in which an IC or portion of an IC is operating. The well-known bandgap reference described above by its nature provides quantities that are proportional to absolute temperature (PTAT) having both positive and negative slopes.

One patented method (US Patent 6786250) efficiently creates a coarse temperature sensing unit from a type of bandgap reference cell. [2] It works by comparing scaled versions of an internal PTAT voltage (having a negative slope) to the circuit's output voltage which is nominally independent of temperature. By this means, this circuit can provide a logical indication of the zone, from among a few coarse temperature zones, in which the circuit is operating. The nominal, desired behavior is shown in Figure 1.

Figure 1: US Patent 6786250 Voltage/Temperature Trip Points


Page 02 of 6

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Unfortunately, modern integrated circuit processing creates a great deal of variation in parameters, both absolute value and matching between components. These variations cause significant departures from the desired behavior. When this circuit was implemented as shown in the patent and analyzed in a circuit simulation tool under all conditions of process, supply voltage, and random mismatch, the curves shown in Figure 2 were obtained. None of the desired temperature zones is visible.

Figure 2: Simulated circuit performance in 130 nm process. Vertical lines are comparator outputs. Horizontal band at 400 mV is the bandgap output (constant over temperature). X axis is temperature.