Analog temperature sensor for digital blocks

The disclosure provides a circuit that includes an analog control block, and a plurality of temperature sensors coupled to the analog control block. At least one temperature sensor of the plurality of temperature sensors includes a first transistor coupled to a first current source. A second transistor is coupled to a second current source and to the first transistor. The analog control block measures a local temperature from a first potential generated across the first transistor and from a second potential generated across the second transistor.

TECHNICAL FIELD

The present disclosure is generally related to temperature sensors, and more particularly to a temperature sensor designed as a standard digital cell.

BACKGROUND

Due to a remarkable growth of portable systems, the demand for low-cost but high performance temperature sensors is on an increasing trend. The important applications of temperature sensors includes the following, but not limited to, (a) power consumption control in integrated chips that includes a processing unit; (b) thermal compensation in application specific integrated circuits; (c) local temperature monitoring in fabrication factories; and (d) temperature control in automobiles and consumer electronic devices.

In addition to low cost and high performance, the power consumption of temperature sensors should be as low as possible to be applicable to the battery-powered portable systems. Furthermore, with low power consumption, the error caused by self-heating will be reduced and the power consumption of the integrated chips will not be significantly increased.

A heat map of an integrated chip illustrates the heat generated and the corresponding temperature in different parts of the integrated chip. Generally, the area around a processing unit or logic unit is the hottest region or hot spot. In a typical integrated chip, there are multiple hot spots. However, owing to a large area of existing temperature sensors, they are placed quiet far away from the hot spot(s). This results in a temperature gradient which can be as high as +/−15° C.

In addition, the temperature gradient is not constant, which further degrades the performance of the existing temperature sensors since a maximum temperature threshold is required to be kept low to account for the temperature gradient. The variation in the temperature gradient may be caused by local hot spots within the processing unit.

Thus, a number of temperature sensors that can be used on the integrated chip are limited because of the large size of the existing temperature sensors. Also, efficient thermal management on the integrated chip is not possible because of the degraded performance of the existing temperature sensors.

The existing temperature sensors also suffer from noise isolation and high process spread. In addition, there are very strict requirements on reference voltage levels and reference current levels. A poor correlation exists between individual temperature sensors which makes it difficult to use multiple temperature sensors on the integrated chips.

The commonly used existing temperature sensor includes time-to-digital converter based CMOS sensors and CMOS gate leakage based sensors. These CMOS sensors have poor linearity and high process spread. In addition, the CMOS sensors are supply sensitive and also susceptible to noise.

SUMMARY

According to an aspect of the disclosure, a circuit is disclosed. The circuit includes an analog control block, and a plurality of temperature sensors coupled to the analog control block. At least one temperature sensor of the plurality of temperature sensors includes a first transistor coupled to a first current source. A second transistor is coupled to a second current source and to the first transistor. The analog control block measures a local temperature from a first potential generated across the first transistor and from a second potential generated across the second transistor.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1is a block diagram of an integrated chip100, according to an embodiment. The integrated chip100includes one or more digital blocks illustrated as104. The digital blocks can be any of the following, but not limited to, processing unit, logic unit, memory modules, testers and interfacing devices. The integrated chip100also includes a plurality of temperature sensors illustrated as temperature sensor (TS)110. The plurality of temperature sensors are coupled to an analog control block120.

The integrated chip100also includes a first digital block104a. The first digital block104ain one example is a processing unit. The heat generated by the first digital block104ais represented as108. The regions similar to region108on the integrated chip are termed as hot spots. Thus, hot spots are the hot regions on the integrated chip100where a large amount of heat is generated by neighboring digital blocks. Each temperature sensor (TS)110of the plurality of temperature sensors is designed as a standard digital cell. This enables to place a temperature sensor (TS)110at hot spots.

In one example, at least one temperature sensor (TS)110of the plurality of temperature sensors includes a first transistor and a second transistor. In one version, each of the first transistor and the second transistor is a diode-connected PNP transistor. The first transistor is coupled to a first current source, and the second transistor is coupled to a second current source. A local temperature is measured from a first potential generated across the first transistor and from a second potential generated across the second transistor.

The local temperature is a temperature of a region in which the temperature sensor (TS)110is placed. For example, a first temperature sensor (TS)110ais coupled to the first digital block104a. The analog control block120measures the local temperature of the first digital block104afrom the first potential and the second potential generated across the first temperature sensor (TS)110a. Thus, the temperature of the region108is measured by the analog control block120.

The diode-connected PNP transistors are designed as standard core cell which allows easy integration with the one or more digital blocks. The temperature sensor (TS)110is designed as a standard digital cell that uses only low level metals. This relaxes the routing constraints of the temperature sensor (TS)110. The design of the temperature sensor (TS)110as standard digital cell makes it compatible with digital placement and routing tools.

In addition, the temperature sensor (TS)110is small in size which allows placement of the temperature sensor (TS)110at hot spots. Also, the temperature sensor (TS)110can be integrated with a digital block104with ease. Thus, the temperature sensor (TS)110provides an accurate measurement of the local temperature. A large number of these temperature sensors can be used to generate a heat map of the integrated chip100.

The temperature sensor (TS)110does not require a separate power supply. The temperature sensor (TS)110can be connected to a common ground which is used by the digital blocks104. The first potential and the second potential generated at the temperature sensor (TS)110are provided to the analog control block120. The analog control block120uses a difference in the first potential and the second potential to generate a digital code. The digital code is used to calculate the local temperature. In one example, a look-up table is used to calibrate the digital code and the local temperature.

In one example, the analog control block120includes a multiplexer which time multiplexes the potential (the first potential and the second potential) obtained from the plurality of temperature sensors. The operation of the temperature sensor (TS)110and the analog control block120are further illustrated later in the description.

FIG. 2illustrates a temperature sensor200, according to an embodiment. The temperature sensor includes a first current source202, a second current source204, a first transistor208and a second transistor212. The first transistor208is coupled to the first current source202. The second transistor212is coupled to the second current source204and the first transistor208. In one example, each of the first transistor208and the second transistor212is a diode-connected PNP transistor.

The first transistor208has an emitter terminal208e, a base terminal208band a collector terminal208c. The second transistor212has an emitter terminal212e, a base terminal212band a collector terminal212c. The base terminal208bof the first transistor208is coupled to the base terminal212bof the second transistor212. The collector terminal208cof the first transistor208and the collector terminal212cof the second transistor212are coupled to a ground terminal214.

The operation of the temperature sensor200illustrated inFIG. 2is explained now. The first current source202and the second current source204pumps current in the first transistor208and the second transistor212respectively. In one version, the first current source202and the second current source204are included in an analog control block which is coupled to the temperature sensor200. The analog control block is similar to the analog control block120illustrated inFIG. 1.

A first potential VBE1216is generated across the first transistor208, and a second potential VBE2218is generated across the second transistor212. The first potential VBE1216is generated across the emitter terminal208eand the base terminal208bof the first transistor208. The first potential VBE1216is measured through a first resistor R1. The second potential VBE2218is generated across the emitter terminal212eand the base terminal212bof the second transistor212. The second potential VBE2218is measure through a second resistor R2. The first resistor R1and the second resistor R2, in one example, represent parasitic routing resistance of metal routes from the analog control block to the first transistor208and the second transistor212respectively.

A local temperature is measured from the first potential VBE1216and the second potential VBE2218. In one example, the analog control block similar to the analog control block120is used to measure the local temperature from the first potential VBE1216and the second potential VBE2218. The local temperature is a temperature of a region in which the temperature sensor200is placed. When the temperature sensor200is coupled to a digital block, the temperature sensor200is used to measure the local temperature of the digital block.

The first transistor208and the second transistor212, in one example, are diode-connected PNP transistors which are designed as standard core cell. This allows easy integration of the temperature sensor200into a digital block. The design of the temperature sensor200as standard digital cell makes it compatible with digital placement and routing tools. In addition, the temperature sensor200is small in size as compared to conventional temperature sensors. This allows placement of the temperature sensor200at hot spots. Hot spots are the hot regions on an integrated chip where a large amount of heat is generated by neighboring digital blocks.

Also, the temperature sensor200can be integrated with a digital block with ease. Thus, the temperature sensor200provides an accurate measurement of the local temperature. A large number of these temperature sensors can be used to generate a heat map of the integrated chip.

FIG. 3illustrates a layout300of a temperature sensor, according to an embodiment. The layout300is explained in connection with the temperature sensor200illustrated inFIG. 2. The layout300illustrates a first transistor308and a second transistor312. The layout illustrates that each of the first transistor308and the second transistor312is a diode-connected PNP transistor.

The first transistor308is similar in connection and operation to the first transistor208, and the second transistor312is similar in connection and operation to the second transistor212. The layout300illustrates that the temperature sensor, for example temperature sensor200, is designed as a standard digital cell that uses only low level metals. This relaxes the routing constraints of the temperature sensor. The design of the temperature sensor as a standard digital cell makes it compatible with digital placement and routing tools.

The diode-connected PNP transistors308and312are designed as standard core cell which allows easy integration with one or more digital blocks. The layout300illustrates that the temperature sensor is small in size which allows placement of the temperature sensor at hot spots in an integrated chip. Thus, the temperature sensor provides an accurate measurement of a local temperature. The local temperature is a temperature of a region in which the temperature sensor is placed. When the temperature sensor is coupled to a digital block, the temperature sensor is used to measure the local temperature of the digital block.

A large number of these temperature sensors can be used to generate a heat map of the integrated chip, for example the integrated chip100. The temperature sensor illustrated in the layout300does not require a separate power supply. Hence, there is no leakage power. The temperature sensor can be connected to a common ground which is used by other digital blocks on the integrated chip. The diode-connected PNP transistors308and312are context friendly cells, and do not affect context sensitive low length transistors placed in the vicinity of these transistors. Thus, the diode-connected PNP transistors308and312do not affect functioning of low length transistors.

A first current source and a second current source pumps current in the first transistor308and the second transistor312respectively. The first current source and the second current source are included in an analog control block which is coupled to the temperature sensor illustrated in layout300. The analog control block is similar to the analog control block120illustrated inFIG. 1.

A first potential VBE1is generated across the first transistor308, and a second potential VBE2is generated across the second transistor312. The first potential VBE1is generated across the emitter terminal and the base terminal of the first transistor308. The second potential VBE2is generated across the emitter terminal and the base terminal of the second transistor312.

The analog control block similar to the analog control block120is used to measure the local temperature from the first potential VBE1and the second potential VBE2. The temperature sensor illustrated in layout300is coupled to an analog control block through four nets. A first net is used to provide current from the first current source in the analog control block to the first transistor308. A second net is used to provide current from the second current source in the analog control block to the second transistor312.

A third net is used by the analog control block to measure the first potential VBE1is generated across the first transistor308. A fourth net is used by the analog control block to measure the second potential VBE2is generated across the second transistor312. All four nets are routed with minimum spacing. Also, shield lines are used around the outermost nets of the four nets. In one version, the first transistor308and the second transistor312are vertical PNP transistors with an emitter active of size 2.5 μm×4 μm and a base region of size 6.5 μm×5 μm.

FIG. 4illustrates an analog control block400, according to an embodiment. The analog control block400includes a multiplexer402, an instrumentation amplifier (IA)404, a unity feedback amplifier (UA)412and an analog-to-digital converter410. In one example, the analog control block400is coupled to one or more temperature sensors. In one version, the analog control block400is integrated on a same chip as the temperature sensors. In another version, the analog control block400is on a different chip as the temperature sensors.

The multiplexer402receives a first potential VBE1416and a second potential VBE2418. In one example, the multiplexer402receives a first potential VBE1416and a second potential VBE2418from a temperature sensor for example, the temperature sensor200illustrated inFIG. 2. The first potential VBE1416is analogous to the first potential VBE1216, and the second potential VBE2418is analogous to the second potential VBE2218.

In another example, the multiplexer402receives the first potential and the second potential generated by multiple temperature sensors. The multiplexer time multiplexes the first potential and the second potential obtained from the one or more temperature sensors. The multiplexer402provides the first potential VBE1416and the second potential VBE2418generated by a temperature sensor to the instrumentation amplifier (IA)404.

The instrumentation amplifier (IA)404measures a difference of the first potential VBE1416and the second potential VBE2418. The instrumentation amplifier (IA)404amplifies the difference of the first potential VBE1416and the second potential VBE2418to generate an amplified voltage406. The unity feedback amplifier (UA)412receives a band gap voltage VBG414, and generates a reference voltage408.

The ADC410is coupled to the instrumentation amplifier (IA)404and the unity feedback amplifier (UA)412. The ADC410receives the amplified voltage406and the reference voltage408. The ADC410converts the amplified voltage406to a digital code420using the reference voltage408. The digital code420is used to measure a local temperature. In one example, a look-up table is used to calibrate the digital code420and the local temperature.

The local temperature is a temperature of a region in which the temperature sensor is placed. When the temperature sensor is coupled to a digital block, the local temperature measured by the analog control block400is the local temperature of the digital block. The operation of the analog control block400is further illustrated in connection withFIG. 5andFIG. 6.

FIG. 5illustrates operation of an analog control block, according to an embodiment. TheFIG. 5is explained in connection with the analog control block400illustrated inFIG. 4and the temperature sensor200illustrated inFIG. 2. Line A illustrates a first potential VBE1and line B illustrates a differential potential ΔVBE. The first potential VBE1is similar to the first potential VBE1216, and ΔVBE represents the difference between the first potential VBE1216and the second potential VBE2218.

The line A represents a relation between the voltage generated across the first transistor208which is VBE1and the temperature. It is defined as

VBE⁢⁢1=η⁢kTq⁢ln⁡(IIs)(1)
where η is an emission coefficient of the emitter base junction, k is Boltzmann's constant, q is the charge of a single electron, T represents absolute temperature, Is represents an emitter saturation current and I represents the current provided to the first transistor208by the first current source202.

The second potential VBE2218is defined as

VBE⁢⁢2=η⁢kTq⁢ln⁡(n*IIs)(2)
where, n*I is the current provided to the second transistor212by the second current source204.

Thus, the differential potential illustrated in line B is defined as

Equation 3 illustrates that the differential potential ΔVBE is directly proportional to the absolute temperature (T), which is also illustrated by line B. This differential potential ΔVBE is measured by an instrumentation amplifier, similar to IA404, in the analog control block400. The instrumentation amplifier amplifies the difference of the first potential VBE1216and the second potential VBE2218to generate an amplified voltage.

An analog-to-digital converter (ADC) is coupled to the instrumentation amplifier. The ADC receives the amplified voltage. The ADC converts the amplified voltage to a digital code. The digital code is used to calculate a local temperature. In one example, a look-up table is used to calibrate the digital code and the local temperature. The local temperature is a temperature of a region in which the temperature sensor, for example temperature sensor200, is placed. When the temperature sensor is coupled to a digital block, the local temperature measured by the analog control block is the local temperature of the digital block.

FIG. 6illustrates operation of an analog control block, according to an embodiment. TheFIG. 6is explained in connection with the analog control block400illustrated inFIG. 4and the temperature sensor200illustrated inFIG. 2. Line A illustrates a first potential VBE1and line B illustrates a second potential VBE2. Line C illustrates a third potential VBE3. The first potential VBE1is generated across a first transistor when a first current is provided to the first transistor.

The second potential VBE2is generated across a second transistor when a second current is provided to the second transistor. Similarly, the third potential is generated across the first transistor when a third current is provided to the first transistor. This is illustrated in connection with the temperature sensor200. The first current is provided to the first transistor208to generate the first potential VBE1. This is illustrated in Line A, and defined as

VBE⁢⁢1=η⁢kTq⁢ln⁡(n*IIs)(4)
where η is an emission coefficient of the emitter base junction, k is Boltzmann's constant, q is the charge of a single electron, T represents absolute temperature, Is represents an emitter saturation current and n*I represents the first current provided to the first transistor208by the first current source202.

The second current is provided to the second transistor212to generate the second potential VBE2. This is illustrated in Line B and defined as

The third current is provided to the first transistor208to generate the third potential VBE3. This is illustrated in Line C and defined as

VBE⁢⁢3=η⁢kTq⁢ln⁡(m*IIS)(6)
where m*I is the third current provided to the first transistor208.

The instrumentation amplifier amplifies the difference of the first potential VBE1216and the second potential VBE2218to generate a first amplified voltage. The first amplified voltage ΔVBE1is defined as

An analog-to-digital converter (ADC) is coupled to the instrumentation amplifier. The ADC receives the first amplified voltage. The ADC converts the first amplified voltage to a first digital code. In one example, when the ADC is a 10 bit ADC, the first digital code is represented as

Code⁡(1)=1023*Δ⁢⁢VBE⁢⁢1VREF(9)
where, VREF is a reference voltage received by the ADC.

The instrumentation amplifier amplifies the difference of the first potential VBE2and the third potential VBE3to generate a second amplified voltage. The second amplified voltage ΔVBE2is defined as

The ADC receives the second amplified voltage. The ADC converts the second amplified voltage to a second digital code. In one example, when the ADC is a 10 bit ADC, the second digital code is represented as

The analog control block sums the first digital code and the second digital code to measure a local temperature. In one example, a look-up table is used to calibrate the sum of the digital codes and the local temperature. The local temperature is a temperature of a region in which the temperature sensor is placed. When the temperature sensor is coupled to a digital block, the local temperature measured by the analog control block is the local temperature of the digital block.

FIG. 7is a flowchart700illustrating a method of sensing temperature, according to an embodiment. At step702, a first current is provided to a first transistor, and at step704, the second current is provided to a second transistor. In temperature sensor200, the first current source202pumps a first current in the first transistor208, and the second current source204pumps a second current in the second transistor212.

At step706, a first potential is generated across the first transistor. A first potential VBE1216is generated across the first transistor208. The first potential VBE1216is generated across the emitter terminal208eand the base terminal208bof the first transistor208. At step708, a second potential is generated across the second transistor. A second potential VBE2218is generated across the second transistor212. The second potential VBE2218is generated across the emitter terminal212eand the base terminal212bof the second transistor212.

At step710, a local temperature is measured from the first potential and the second potential. A local temperature is measured from the first potential VBE1216and the second potential VBE2218. In one example, the analog control block similar to the analog control block120is used to measure the local temperature from the first potential VBE1216and the second potential VBE2218. The local temperature is a temperature of a region in which the temperature sensor200is placed. When the temperature sensor200is coupled to a digital block, the temperature sensor200is used to measure the local temperature of the digital block.

The first transistor and the second transistor, in one example, are diode-connected PNP transistors which are designed as standard core cell. A temperature sensor having the first transistor and the second transistor is designed as a digital cell.

FIG. 8illustrates a computing device800, according to an embodiment. The computing device800is, or is incorporated into, a mobile communication device, such as a mobile phone, a personal digital assistant, a transceiver, a personal computer, or any other type of electronic system. The computing device800may include one or more additional components known to those skilled in the relevant art and are not discussed here for simplicity of the description.

In some embodiments, the computing device800comprises a megacell or a system-on-chip (SoC) which includes a processing unit812such as a CPU (Central Processing Unit), a memory module814(e.g., random access memory (RAM)) and a tester810. The processing unit812can be, for example, a CISC-type (Complex Instruction Set Computer) CPU, RISC-type CPU (Reduced Instruction Set Computer), or a digital signal processor (DSP).

The memory module814(which can be memory such as RAM, flash memory, or disk storage) stores one or more software applications830(e.g., embedded applications) that, when executed by the processing unit812, performs any suitable function associated with the computing device800. The tester810comprises logic that supports testing and debugging of the computing device800executing the software applications830.

For example, the tester810can be used to emulate a defective or unavailable component(s) of the computing device800to allow verification of how the component(s), were it actually present on the computing device800, would perform in various situations (e.g., how the component(s) would interact with the software applications830). In this way, the software applications830can be debugged in an environment which resembles post-production operation.

The processing unit812typically comprises memory and logic which store information frequently accessed from the memory module814. A camera818is coupled to the processing unit812. The computing device800includes an analog control block816. The analog control block816is coupled to the processing unit812and the memory module814. The computing device800also includes a plurality of temperature sensors illustrated as TS820. The plurality of temperature sensors are coupled to the analog control block816.

Each temperature sensor (TS)820of the plurality of temperature sensors is designed as a standard digital cell. This enables to place a temperature sensor (TS)820at hot spots. Hot spots are the hot regions on the computing device800where a large amount of heat is generated by digital blocks such as processing unit812and the memory module814.

In one example, at least one temperature sensor (TS)820of the plurality of temperature sensors includes a first transistor and a second transistor. On one version, each of the first transistor and the second transistor is a diode-connected PNP transistor. The first transistor is coupled to a first current source, and the second transistor is coupled to a second current source. A local temperature is measured from a first potential generated across the first transistor and from a second potential generated across the second transistor.

The local temperature is a temperature of a region in which the temperature sensor (TS)820is placed. The analog control block816measures the local temperature from the first potential and the second potential generated across a temperature sensor (TS)820. The diode-connected PNP transistors are designed as standard core cell which allows easy integration with the one or more digital blocks. The temperature sensor (TS)820is designed as a standard digital cell that uses only low level metals. This relaxes the routing constraints of the temperature sensor (TS)820. The design of the temperature sensor (TS)820as standard digital cell makes it compatible with digital placement and routing tools.

In addition, the temperature sensor (TS)820is small in size which allows placement of the temperature sensor (TS)820at hot spots. Also, the temperature sensor (TS)820can be integrated with a digital block with ease. Thus, the temperature sensor (TS)820provides an accurate measurement of the local temperature. A large number of these temperature sensors can be used to generate a heat map of the computing device800.

The temperature sensor (TS)820does not require a separate power supply. The first potential and the second potential generated at the temperature sensor (TS)820are provided to the analog control block816. The analog control block816uses a difference in the first potential and the second potential to generate a digital code. The digital code is used to calculate the local temperature. In one example, a look-up table is used to calibrate the digital code and the local temperature.

The foregoing description sets forth numerous specific details to convey a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the invention may be practiced without these specific details. Well-known features are sometimes not described in detail in order to avoid obscuring the invention. Other variations and embodiments are possible in light of above teachings, and it is thus intended that the scope of invention not be limited by this Detailed Description, but only by the following Claims.