JP6791648B2 - A / D converter circuit and electronic equipment - Google Patents

Description

The present invention relates to an A / D converter.

Sensors that measure electrical and physical conditions are used in a variety of applications. The output of many sensors is an analog signal, and it is necessary to convert it into a digital signal in order to process the digital signal by a processor such as a microcomputer. In applications where such accuracy is not required, it is possible to use the A / D converter built into the microcomputer, but in applications where high accuracy is required, A / D converters with high accuracy are integrated. A D converter IC (Integrated Circuit) is used.

FIG. 1 is a block diagram of a signal processing system 10r including an A / D converter IC (Integrated Circuit) 100r examined by the present inventor. The signal processing system 10r includes a sensor 12, a microcomputer 20r, and an A / D converter IC100r. Examples of the sensor 12 include a temperature sensor, a current sensor, and a voltage sensor. The A / D converter IC100r receives the analog input signal S1 from the sensor 12 and converts it into the digital signal S2. The microcomputer 20r processes the digital signal S2 generated by the A / D converter IC100r.

The A / D converter IC100r includes an A / D converter 102, a bandgap reference (BGR) circuit 104, a buffer 106, and an interface circuit 108. The A / D converter 102 converts the analog input signal S1 into the digital signal S2. The BGR circuit 104 generates a temperature-independent reference voltage V _BGR . The buffer 106 supplies the reference voltage V _BRG to the A / D converter 102. The A / D converter 102 converts the analog input signal S1 into the digital signal S2 by using the reference voltage V _BRG . The digital signal S2 is transmitted from the interface circuit 108 to the interface circuit 22 of the microcomputer 20r.

The A / D converter IC100r is designed so that the temperature dependence (temperature drift) of the input / output characteristics of the A / D converter IC100r is small, and therefore, the temperature characteristics of the reference voltage _VBGR generated by the BGR circuit 104 are also such a viewpoint. Optimized from.

However, when the temperature dependence of the circuit block other than the A / D converter IC100r, for example, the sensor 12 is large, the temperature drift of the signal processing system 10r as a whole becomes a problem.

Alternatively, the A / D converter IC100r may be designed so that the temperature dependence (temperature drift) of the input / output characteristics becomes small in combination with a predetermined standard external circuit, and therefore the reference generated by the BGR circuit 104. The temperature characteristics of the voltage V _BGR can also be optimized from that perspective. However, when the designer of the signal processing system 10r combines the A / D converter IC100r with an external circuit different from the standard external circuit, the temperature drift of the signal processing system 10r as a whole becomes a problem.

In order to correct the temperature drift of the entire signal processing system 10r, the microcomputer 20r includes an interface circuit 22, a correction processing unit 24, a correction table 26, and a signal processing unit 28. The correction processing unit 24 corrects the digital signal S3 received by the interface circuit 22 according to the temperature T. The correction table 26 stores correction information at each temperature T. The signal processing unit 28 performs predetermined signal processing on the corrected digital signal S4.

Japanese Unexamined Patent Publication No. 2011-101247 Japanese Unexamined Patent Publication No. 2014-171035

As a result of examining the signal processing system 10r of FIG. 1, the present inventors have come to recognize the following problems. The function of the correction processing unit 24 is realized by software-controlling the arithmetic processing unit of the microcomputer 20r. Therefore, when the number of bits of the digital signal S3 is 16 bits or more, the arithmetic processing of the arithmetic processing unit of the microcomputer 20r becomes heavy, so that a high-performance microcomputer 20r is required and the cost increases.

Further, since the correction table 26 needs to be stored in the ROM (Read Only Memory), if the amount of data is large, the cost becomes high.

The present inventor has been made in view of such a problem, and one of the exemplary purposes of the embodiment is to provide an A / D converter circuit capable of reducing the temperature drift of a signal processing system.

One aspect of the present invention relates to an A / D converter circuit that converts an analog signal into a digital signal. The A / D converter circuit is a reference bias circuit that generates a reference voltage. The reference bias circuit is configured so that the temperature dependence of the reference voltage can be selected from a plurality of reference voltages, and the analog signal is digitally referred to by referring to the reference voltage. It includes an A / D converter that converts a signal.

According to this aspect, the temperature drift of the entire signal processing system can be corrected by selecting the temperature dependence of the reference bias circuit in consideration of the temperature characteristics of the external circuit and the element of the A / D converter circuit.

In some embodiments, it is not necessary to correct the temperature drift in the digital signal processing in the subsequent processor, or the processing can be simplified. As a result, the amount of calculation by the processor can be reduced.

The reference bias circuit may include a reference voltage circuit in which the temperature dependence of the output voltage can be selected from a plurality.

The reference voltage circuit includes a bandgap reference circuit that generates a voltage obtained by adding a PTAT (Proportional to Absolute Temperature) voltage and a CATT (Complementary to Absolute Temperature) voltage, and includes at least one coefficient of the PTAT voltage and the CATT voltage. May be variable.

The A / D converter circuit of some embodiment may further include a buffer circuit that receives the output voltage of the reference voltage circuit and supplies the reference voltage to the A / D converter. The offset of the buffer circuit may be selectable from a plurality. As a result, in addition to the temperature dependence of the reference voltage, the offset amount can be controlled, and the temperature drift of the entire signal processing system can be further suppressed.

The temperature dependence in the reference voltage circuit and the offset in the buffer circuit may be selected based on a common control signal. In this case, control can be simplified.

The temperature dependence in the reference voltage circuit and the offset in the buffer circuit may be individually and independently set. This allows temperature drift to be compensated for on a wider variety of platforms.

The A / D converter circuit of some embodiment may further include a buffer circuit that receives the output voltage of the reference voltage circuit and supplies the reference voltage to the A / D converter. The offset of the buffer circuit may be selectable from a plurality. As a result, in addition to the temperature dependence of the reference voltage, the offset amount can be controlled, and the temperature drift of the entire signal processing system can be further suppressed.

The gain of the buffer circuit may be selectable from a plurality. The control signal instructing the temperature dependence in the reference voltage circuit and the control signal instructing the gain in the buffer circuit may be the same.

The temperature dependence in the reference voltage circuit and the gain in the buffer circuit may be individually and independently set.

In some embodiments, the A / D converter circuit is connected to a register that stores a control signal that indicates the temperature dependence of the reference voltage and an external processor that processes the digital signal, outputs the digital signal to the processor, and outputs the control signal. May further include an interface circuit that receives the signal from the processor and writes it to the register.

The A / D converter circuit may include a non-volatile memory for storing a control signal indicating the temperature dependence of the reference voltage.
By writing the control signal to the non-volatile memory in advance, it is not necessary to write the control signal to the register every time the A / D converter circuit is started.

The A / D converter may be a ΔΣ A / D converter. Since the ΔΣA / D converter has a large number of bits and therefore the cost of drift correction by digital signal processing is high, the effect of reducing the calculation of the processor can be further enjoyed.

An A / D converter circuit of a certain aspect includes a plurality of input terminals capable of inputting analog input signals, a multiplexer that selects one of the plurality of input terminals, an amplifier that amplifies the output signal of the multiplexer, and an amplifier. It may further include a filter for filtering the output signal of.

The A / D converter circuit of a certain aspect may be integrally integrated on one semiconductor substrate. "Integrated integration" includes cases where all the components of a circuit are formed on a semiconductor substrate or cases where the main components of a circuit are integrated integrally, and some of them are used for adjusting circuit constants. A resistor, a capacitor, or the like may be provided outside the semiconductor substrate. By integrating the circuits on one chip, the circuit area can be reduced and the characteristics of the circuit elements can be kept uniform.

Another aspect of the invention relates to electronic devices. The electronic device includes a sensor, any of the above-mentioned A / D converter circuits that receive an analog signal from the sensor and convert it into a digital signal, and a processor that processes a digital signal generated by the A / D converter circuit. ..

It should be noted that any combination of the above components and the conversion of the expression of the present invention between methods, devices and the like are also effective as aspects of the present invention.

According to an aspect of the present invention, the temperature drift of the entire signal processing system can be corrected.

It is a block diagram of the signal processing system including the A / D converter IC examined by this inventor. It is a block diagram of the signal processing system including the A / D converter IC which concerns on embodiment. It is a figure which shows an example of the temperature dependence of a reference voltage V _REF . It is a circuit diagram which shows the structural example of the reference bias circuit. It is a conceptual diagram of a generalized reference voltage circuit. It is a figure which shows the temperature dependence of the bandgap reference voltage V _BGR of FIG. It is a block diagram of an electronic device provided with an A / D converter IC.

Hereinafter, the present invention will be described with reference to the drawings based on preferred embodiments. The same or equivalent components, members, and processes shown in the drawings shall be designated by the same reference numerals, and redundant description will be omitted as appropriate. Further, the embodiment is not limited to the invention but is an example, and all the features and combinations thereof described in the embodiment are not necessarily essential to the invention.

FIG. 2 is a block diagram of a signal processing system 10 including the A / D converter IC 100 according to the embodiment. The signal processing system 10 includes a sensor 12, an A / D converter IC 100, and a processor 20.

The sensor 12 is a current sensor, a voltage sensor, a temperature sensor, a distance measuring meter, an angle sensor, a gyro sensor, or the like, and generates an analog signal S1 according to an electrical state or a physical state of a measurement target.

The A / D converter IC 100 converts the analog input signal S1 into a digital signal S2 and outputs it to the processor 20 in the subsequent stage. The processor 20 processes a digital signal from the A / D converter IC 100. The processor 20 may be a microcomputer, a DSP (Digital Signal Processor), a CPU (Central Processing Unit), or the like.

The A / D converter IC 100 includes an A / D converter 102, a reference bias circuit 110, a buffer 106, and an interface circuit 108. The reference bias circuit 110 generates a reference voltage V _REF and supplies it to the reference voltage terminal of the A / D converter 102. The A / D converter 102 converts the analog signal S1 into the digital signal S2 based on the reference voltage V _REF generated by the reference bias circuit 110. It should be noted that the full scale range of the A / D converter 102 or the voltage width of 1 LSB is determined based on the reference voltage V _REF .

The type of the A / D converter 102 is not particularly limited, but the present invention is particularly effective in a type such as a ΔΣ A / D converter that requires high accuracy and is susceptible to temperature drift requirements. Further, the A / D converter 102 may be of a differential type or a single-ended type.

The interface circuit 108 receives the digital signal S2 and transmits it to the processor 20. The interface circuit 22 of the processor 20 receives the digital signal S2, and the signal processing unit 28 processes the digital signal S3 received by the interface circuit 22. Interface circuit 108 and interface circuit 22, for example, ^I 2 C (Inter IC) can be used an interface or SPI (Serial Peripheral Interface), it is not particularly limited.

In the present embodiment, the reference bias circuit 110 is configured so that the temperature dependence of the reference voltage V _REF , which is the output thereof, can be selected from a plurality. The temperature dependence of the reference voltage V _REF is selected based on the control signal S5. FIG. 3 is a diagram showing an example of the temperature dependence of the reference voltage V _REF . In this example, one temperature dependence can be selected from the five types (i) to (v). The number of temperature-dependent options is not limited to 5, and may be larger or smaller. The temperature dependence (shape) of each of the plurality of reference voltages V _REF is not particularly limited.

Return to FIG. The A / D converter IC 100 is provided with a register 120 for storing the control signal S5. The interface circuit 108 receives the control signal S5 from the processor 20 and writes it to the register 120.

The above is the configuration of the signal processing system 10. Next, the operation will be described.
The designer of the signal processing system 10 provides a plurality of options provided by the A / D converter IC 100 for temperature dependence that reduces the temperature drift of the digital signal S3 input to the processor 20 at the design stage of the signal processing system 10. Decide from among. Then, the control signal S5 instructing the determined option is stored in the ROM outside or inside the processor 20.

When the signal processing system 10 is used, the processor 20 transmits the control signal S5 to the A / D converter IC 100 at the time of setup after the power is turned on, and the temperature dependence of the reference voltage V _REF of the reference bias circuit 110. To instruct. The A / D converter 102 converts the analog input signal S1 into the digital signal S2 with reference to the reference voltage V _REF having a temperature dependence according to the control signal S5.

The above is the operation of the signal processing system 10. According to this signal processing system 10, by giving an appropriate control signal S5 to the A / D converter IC 100, the temperature drift of the entire signal processing system 10 including the sensor 12 is reduced, not the A / D converter IC 100 alone. it can.

As a result, the temperature drift correction process in the processor 20 becomes unnecessary, or the process can be minimized. That is, since the computing load of the processor 20 can be reduced, it is possible to use hardware that is slower than that in FIG. 1, and the cost of the processor 20 can be reduced.

Further, since the correction table is not required, the memory capacity can be reduced, and the cost can be further reduced as compared with FIG.

The present invention extends to various devices and circuits grasped as the block diagram and circuit diagram of FIG. 2 or derived from the above description, and is not limited to a specific configuration. Hereinafter, more specific configuration examples and examples will be described not for narrowing the scope of the present invention but for helping the understanding of the essence of the invention and the circuit operation and clarifying them.

FIG. 4 is a circuit diagram showing a configuration example of the reference bias circuit 110. The reference bias circuit 110 includes a reference voltage circuit 112 and a buffer circuit 114. The reference voltage circuit 112 is configured so that the temperature dependence of its output voltage V _BGR can be selected from a plurality. Preferably, the reference voltage circuit 112 is composed of a bandgap reference circuit. The bandgap reference circuit adds a PTAT (Proportional to Absolute Temperature) voltage and a CATT (Complementary to Absolute Temperature) voltage to generate a bandgap reference voltage V _BGR .

The bandgap reference circuit of FIG. 4 includes transistors Q1 and Q2, resistors R1 to R3, and an operational amplifier (differential amplifier) 116. For example, the resistor R3 may be a variable resistor, and the resistance value may be switched according to the control signal S5. As a result, the addition coefficient of the PTAT voltage and the CATT voltage becomes variable, and the temperature characteristic of the bandgap reference voltage V _BGR can be switched.

The configuration of this bandgap reference circuit is only an example, and various known types of bandgap reference circuits can be used. FIG. 5 is a conceptual diagram of a more generalized reference voltage circuit 112. The PTAT circuit 130 produces a PTAT voltage with a positive temperature coefficient, and the CDAT circuit 132 produces a CATT voltage with a negative temperature coefficient. The adder 134 adds the PTAT voltage V _PTAT and the CATT voltage V _CATT to generate the bandgap reference voltage V _BGR . The addition coefficient in the adder 134 can be switched according to the control signal S5.

FIG. 6 is a diagram showing the temperature dependence of the bandgap reference voltage V _BGR of FIG. By changing the coefficient of addition in the bandgap reference circuit, the temperature T _{0 at} which the temperature dependence is zero (dV _BGR / dT = 0) can be changed. With reference to FIG. 6, it should be noted that when the temperature T ₀ is changed, not only the slope of the bandgap reference voltage V _REF but also the voltage range changes significantly.

Return to FIG. The buffer circuit 114 receives the bandgap reference voltage V _BGR and generates a reference voltage V _REF . The buffer circuit 114 can switch at least one or both of its offset and gain. That is, the buffer circuit 114 is configured so that its offset (or gain) can be selected from a plurality. This makes it possible to shift the bandgap reference voltage V _BGR shown in FIG. 6 in the vertical direction. As a result, it becomes possible to generate a reference voltage V _REF as shown in FIG. That is, the buffer circuit 114 may eliminate the vertical variation of the plurality of bandgap reference voltages V _BGR .

Alternatively, if the analog signal S1 from the sensor 12 has a different offset depending on the type of the sensor 12, the buffer circuit 114 can be used to cancel the offset.

The configuration of the buffer circuit 114 is not particularly limited, and may be configured by, for example, a non-inverting amplifier or a linear regulator. The offset or gain can be adjusted by making the feedback resistor _RFB a variable resistor or by making the offset voltage of the operational amplifier OA variable.

The temperature dependence in the reference voltage circuit 112 and the gain (or offset) in the buffer circuit 114 may be selected based on the common control signal S5. As a result, the temperature dependence of the reference voltage V _REF can be specified by giving one control signal S5 from the processor 20.

Alternatively, the temperature dependence in the reference voltage circuit 112 and the gain (or offset) in the buffer circuit 114 may be individually and independently controllable. That is, the control signal S5a of the reference voltage circuit 112 and the control signal S5b of the buffer circuit 114 may be written to separate registers. In this case, since it is possible to combine the temperature dependence of the reference voltage V _REF (inclination or the point of T ₀ ) and the amount of shift in the vertical direction, the designer of the signal processing system 10 is asked about the temperature drift correction. , Can provide many degrees of freedom.

(Use)
FIG. 7 is a block diagram of an electronic device 400 including an A / D converter IC 300. The electronic device 400 is, for example, a battery-powered type, and examples thereof include a smartphone, a tablet terminal, and a notebook PC.

For example, the signal processing system 10 can be used for detecting the state of charge (SOC) of the battery 402 of the electronic device 400. The A / D converter IC 300 is configured using the architecture of the A / D converter IC 100 described above.

An analog input signal can be input from the outside to each of the plurality of input terminals IN1 to INM (M is an integer) of the A / D converter IC300. For example, at the input terminal IN, a signal indicating the voltage _{VBAT of the} battery 402, a temperature detection signal from the temperature sensor 404 such as a thermistor or a thermocouple, and a current detection signal corresponding to the voltage drop of the sense resistor _RS for detecting the battery current. Etc. are entered.

The multiplexer 302 selects a plurality of input terminals IN1 to INM in a time division manner. The amplifier 304 is a programmable gain amplifier (PGA) that amplifies the output signal of the multiplexer 302. The filter 306 filters the output signal of the amplifier 304. The ΔΣA / D converter 308 converts the output signal V _IN of the filter 306 into a digital signal D _OUT . The logic circuit 310 applies predetermined signal processing to the digital signal D _OUT from the ΔΣ A / D converter 308. Interface circuit 312, SPI is (Serial Peripheral Interface) or ^I 2 C (Inter IC) interface, external to the processor 20, and outputs the digital signal. The processor 20 estimates or measures the remaining amount of the battery 402 based on the digital signal from the A / D converter IC 300. For estimating the remaining amount of the battery 402, a Coulomb count method, an OCV method using the open circuit voltage (OCV) of the battery 402, or the like can be used.

The application of the A / D converter IC100 is not particularly limited, and it can be used in various applications that require high accuracy.

The present invention has been described above based on the embodiments. This embodiment is an example, and it will be understood by those skilled in the art that various modifications are possible for each of these components and combinations of each processing process, and that such modifications are also within the scope of the present invention. is there. Hereinafter, such a modification will be described.

(First modification)
In the embodiment, the temperature dependence of the reference voltage V _REF is selected by writing the control signal S5 to the register 120, but the present invention is not limited thereto. A non-volatile memory for storing the control signal S5 may be provided, and the value of the control signal S5 may be stored in the A / D converter IC 100 before the A / D converter IC 100 is shipped. As a result, it is not necessary to write the control signal S5 every time the signal processing system 10 is started, so that the processing can be simplified.

(Second modification)
In FIG. 2, it is assumed that the correction processing unit 24 of the processor 20 is completely absent, but a simplified correction processing unit may be provided. For example, if the calculation is equivalent to the processing of the buffer circuit 114 in FIG. 4, the amount of calculation is small, so that the calculation may be performed by the processor 20. In this case, the characteristics of the buffer circuit 114 may be fixed.

Although the present invention has been described based on the embodiments, the embodiments merely show the principles and applications of the present invention, and the embodiments include the ideas of the present invention defined in the claims. Many modifications and arrangements can be changed as long as they do not separate.

10 ... Signal processing system, 12 ... Sensor, 20r ... Microcomputer, 20 ... Processor, 22 ... Interface circuit, 24 ... Correction processing unit, 26 ... Correction table, 28 ... Signal processing unit, 100 ... A / D converter IC, 102 ... A / D converter, 104 ... BGR circuit, 106 ... buffer, 108 ... interface circuit, 110 ... reference bias circuit, 112 ... reference voltage circuit, 114 ... buffer circuit, 120 ... register, S1 ... analog input signal, S2 ... digital signal , S5 ... Control signal, 300 ... A / D converter IC, 302 ... multiplexer, 304 ... amplifier, 306 ... filter, 308 ... ΔΣ A / D converter, 310 ... logic circuit, 312 ... interface circuit.

Claims (14)

An A / D converter circuit that receives an analog signal based on the output of a sensor that measures an electrical or physical state and converts it into a digital signal.
A reference bias circuit that generates a reference voltage and is configured so that the temperature dependence of the reference voltage can be selected from a plurality of reference bias circuits.
An A / D converter that converts the analog signal into the digital signal with reference to the reference voltage.
Registers and
Receiving a control signal from the processor at power up of the A / D converter circuit, and stores in the register, and an interface circuit for transmitting the digital signal to the processor,
The temperature dependence of the reference voltage in the reference bias circuit is selected based on the control signal stored in the register when the power of the A / D converter circuit is turned on.
The control signal is characterized in that the temperature drift of the digital signal received by the processor is determined to be small at the design stage of the signal processing system including the sensor, the A / D converter circuit and the processor. A / D converter circuit. The A / D converter circuit according to claim 1, wherein the reference bias circuit includes a reference voltage circuit in which the temperature dependence of the output voltage can be selected from a plurality. The reference voltage circuit includes a bandgap reference circuit that generates a voltage obtained by adding a PTAT (Proportional to Absolute Temperature) voltage and a CATT (Complementary to Absolute Temperature) voltage, and includes at least the PTAT voltage and the CATT voltage. The A / D converter circuit according to claim 2, wherein one of the coefficients is variable. The reference bias circuit further includes a buffer circuit that receives the output voltage of the reference voltage circuit and supplies the reference voltage to the A / D converter.
The A / D converter circuit according to claim 2 or 3, wherein the buffer circuit can be selected from a plurality of offsets. The A / D converter circuit according to claim 4, wherein the temperature dependence in the reference voltage circuit and the offset in the buffer circuit are selected based on a common control signal. The A / D converter circuit according to claim 4, wherein the temperature dependence in the reference voltage circuit and the offset in the buffer circuit can be individually and independently set. The reference bias circuit further includes a buffer circuit that receives the output voltage of the reference voltage circuit and supplies it to the A / D converter.
The A / D converter circuit according to claim 2 or 3, wherein the buffer circuit can be selected from a plurality of gains. The A / D converter circuit according to claim 7, wherein the temperature dependence in the reference voltage circuit and the gain in the buffer circuit are selected based on a common control signal. The A / D converter circuit according to claim 7, wherein the temperature dependence in the reference voltage circuit and the gain in the buffer circuit can be set individually and independently. The A / D converter circuit according to any one of claims 1 to 9 , further comprising a non-volatile memory for storing the control signal. The A / D converter circuit according to any one of claims 1 to 10 , wherein the A / D converter is a ΔΣ A / D converter. Multiple input terminals that can input analog input signals to each,
A multiplexer that selects one of the plurality of input terminals, and
An amplifier that amplifies the output signal of the multiplexer and
A filter that filters the output signal of the amplifier and
The A / D converter circuit according to any one of claims 1 to 11 , further comprising. The A / D converter circuit according to any one of claims 1 to 12 , wherein the A / D converter circuit is integrally integrated on one semiconductor substrate. With the sensor
The A / D converter circuit according to any one of claims 1 to 13 , which receives an analog signal from the sensor and converts it into a digital signal.
A processor that processes the digital signal generated by the A / D converter circuit, and
An electronic device characterized by being equipped with.

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