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Low power temperature window detection circuit

IP.com Disclosure Number: IPCOM000241124D
Publication Date: 2015-Mar-27
Document File: 4 page(s) / 462K

Publishing Venue

The IP.com Prior Art Database

Abstract

Here is presented a circuit to detect temperature window. This temperature window may be fixed or programmable. The programmable temperature window may be used to build a trimming system with values for each different temperature. The presented circuit use PTAT and CTAT currents to detect temperature windows with same range span over all temperature range of interest (-40oC to +150oC). The circuit is suitable for low power implementations.

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Low power temperature window detection circuit

Abstract

Here is presented a circuit to detect temperature window. This temperature window may be fixed or programmable. The programmable temperature window may be used to build a trimming system with values for each different temperature.

The presented circuit use PTAT and CTAT currents to detect temperature windows with same range span over all temperature range of interest (-40oC to +150oC). The circuit is suitable for low power implementations.

Introduction

Nowadays many products use trimming to increase the accuracy of analog parameters. However, a single trimming over the whole temperature range is limited due to non-null temperature coefficient of the parameters. This limitation can be minimized by using a temperature window trimming approach.

Windowed trimming can increase the precision of a parameter in an order of magnitude. It requires the detection if the silicon is within or outside a temperature window. For each window, the proper parameter trim is applied. A detection circuit suitable for a low power implementation is proposed.

Other applications for this circuit include thermometer and low power wake up based on temperature. In addition, this technique can be used to achieve a high accuracy circuit or to improve simpler circuits to save area and/or test time.

Figure 1 Windowed temperature parameter trimming

Figure 1 depicts the windowed trimming of an arbitrary parameter P. Trimming steps for each temperature window (in red) are applied to the untrimmed parameter (in blue). The green curve shows the trimmed result. It is possible to set trimming values during SoC test with two temperature measurements and appropriate interpolation and/or extrapolation (linear, polynomial, etc.) to set other temperature windows.

Circuit

Figure 2 shows a simplified circuit diagram with the main components:

·         A PTAT (proportional to temperature) and a CTAT (complementary to temperature) currents sources applied to resistor ladders. These sources may be generated with a bandgap circuit.

·         Resistor ladders with many resistors of value R and four with value xR.

·         A set of switches (k0 to km) to select the center of the temperature window (Ts).

·         Two comparators to detect the upper and lower bounds of the temperature window.

·         A control logic block.

Figure 2 - Windowed temperature circuit

The temperature window span ΔT is a function of the xR resistors. The center of the temperature window, Ts, can be set selecting one of the switches k0 to km. The voltage drop in the switches is not a problem since only the voltage difference is taken...