509results about How to "Small temperature coefficient" patented technology

The invention discloses a 2:17 type samarium-cobalt sintered magnet material and a preparation method thereof. The 2:17 type samarium-cobalt sintered magnet material comprises the following raw materials in percentage by mass: 10 to 25 percent of samarium, 45 to 55 percent of cobalt, 10 to 20 percent of iron, 3 to 9 percent of copper, 1 to 3 percent of zirconium and 5 to 15 percent of at least one heavy rear earth element. Due to the selection and the proportion of the raw materials and the innovation of the sintering process, a microstructure of the magnet material is optimized, and the aims of reducing the temperature coefficient of a magnet and simultaneously maintaining higher magnetic energy product of the magnet are fulfilled, wherein the magnetic energy product of the prepared magnet is 14 to 25 MGsOe, the residual magnetism temperature coefficient is about -0.005 to -0.03 percent per DEG C, and a lower magnetic flux temperature coefficient is maintained in an environment at the temperature of between -35 and 300 DEG C.

The invention relates to a rare earth permanent magnetic material and a preparation method thereof. The rare earth permanent magnetic material comprises a (Pr, Nd)-Fe-R-Co-Al-Cu-B-M system, and the rare earth as a main phase component has a phase volume ratio of 90%-98%; wherein R is at least two elements selected from Nb, Tb, Dy and Ho; M is at least two nanometer crystalline oxides with particle size of 10-100 nm selected from ZrO2, MgO and ZnO; and the weight of the nanometer crystalline oxides is 0.1%-3% of the total weight. The rare earth permanent magnetic material is a compound nanometer oxidizer enhanced and sintered praseodymium (Pr)-neodymium (Nd)-based permanent magnet with high coercitive force. The inventive product has magnetic features of low temperature coefficient, high coercitive force, low cost and 220 DEG C working temperature, and can overcome the shortcomings of lower coercitive force, high temperature coefficient and high cost of the prior sintered Nd-Fe-B permanent magnet and the sintered samarium-cobalt magnet in application of large motor products. The preparation method provides a powerful guarantee for realizing the positive effects.

The invention provides an output voltage adjustable CMOS reference voltage source to facilitate the realization of the standard CMOS process, which includes the start circuit, the positive temperature coefficient current generating circuit, the negative temperature coefficient current generating circuit, and the reference voltage generating circuit; the output of the start circuit connecting with the input of the positive temperature coefficient current generating circuit, the first output of the positive temperature coefficient current generating circuit respectively connecting with the first input of the negative temperature coefficient current generating circuit and the third input of the reference voltage generating circuit, the second output of the positive temperature coefficient current generating circuit respectively connecting with the second input of the negative temperature coefficient current generating circuit and the fourth input of the reference voltage generating circuit, the first and second outputs of the negative temperature coefficient current generating circuit respectively corresponding connecting with the first and second inputs of the reference voltage generating circuit, and the reference voltage generating circuit has the reference voltage output to output reference voltage.

The invention discloses a bandgap reference voltage source with wide input range and high power supply rejection ratio. The bandgap reference voltage source comprises a voltage preconditioning circuit and a bandgap reference nuclear circuit, wherein the voltage preconditioning circuit generates preconditioning voltage Vreg with low temperature excursion and the high power supply rejection ratio for supplying power to the bandgap reference nuclear circuit; the bandgap reference nuclear circuit comprises a starting circuit, a negative temperature coefficient current ICTAT generating circuit, a positive temperature coefficient current IPTAT generating circuit and a nonlinear current INL generating circuit; the nonlinear current INL generating circuit is used for compensating a high-order temperature component in the negative temperature coefficient current ICTAT generating circuit; current ICTAT, current IPTAT and current INL are superimposed to obtain reference voltage Vref with an approximate zero temperature coefficient by a current-voltage conversion circuit.

The invention discloses a band gap voltage reference source. The band gap voltage reference source comprises a biasing circuit, a start circuit and a first-order reference circuit, and is characterized by also comprising a temperature compensation circuit and an error amplifier circuit, wherein the temperature compensation circuit comprises an NPN transistor, a first N-channel metal oxide semiconductor (NMOS) transistor, a fifth resistor, a sixth resistor and a seventh resistor. In the band gap voltage reference source provided by the invention, temperature compensation is realized, namely a reference voltage is obtained by adding a collector current and the drain current of a metal oxide semiconductor (MOS) transistor in a sub-threshold region of a bipolar device into a conventional first-order temperature compensation band gap reference circuit, so that an output reference voltage has a smaller temperature coefficient.

The invention provides an ultralow temperature drift high power supply rejection ratio band-gap reference voltage source, and relates to the field of analog integrated circuit design. Mainly aimed at problems of temperature drift and power supply rejection ratio of an existing reference source, a comprehensive solution is provided. The band-gap reference voltage source comprises an independent current source circuit, a biasing circuit, a band-gap core circuit, and a PSRR enhancing circuit. The independent current source circuit is used to generate current which is basically independent of supply voltage to supply power. The bias circuit generates bias voltage used for operational amplification of the band-gap core circuit. The band-gap core circuit uses temperature compensation to obtain reference voltage. The power supply rejection ratio (PSRR) enhancing circuit provides grid bias voltage of the band-gap core circuit and improves power supply rejection ratio. Beneficial effects of the band-gap reference voltage source are that temperature coefficient of band-gap reference is greatly reduced, and power supply rejection ratio is improved. The band-gap reference voltage source is suitable to be used for a radio frequency identification power management module.

The invention discloses a bandgap reference voltage source which comprises a starting circuit, a core bandgap reference circuit and a high-order compensation circuit. The core bandgap reference circuit comprises PMOS tubes M1, M2 and M3, NPN triodes Q1 and Q2 and resistance units R1, RB1, RB2 and RA; and the high-order compensation circuit comprises PMOS tubes M4, M5, M6, M7, M8, M9, M10 and M11, NPN triodes Q3, Q4, Q5, Q6, Q7 and Q8 and resistance units R2 and R3. The bandgap reference voltage source disclosed by the invention adopts the high-order compensation circuit, thereby the temperature coefficient is reduced greatly; the circuits adopt the resistance ratio, thus the circuits can not be affected by the absolute value of the resistance, and the influence of the temperature coefficient of the resistance to the output quantity can be reduced. The bandgap reference voltage source has high power supply rejection ratio and can ensure that the circuits can resist the interference of a power supply.

The invention provides a high-order temperature compensation band gap reference circuit. The high-order temperature compensation band gap reference circuit comprises a start circuit, a bipolar band gap reference circuit, a segmental linear temperature compensation circuit and a delta VGS temperature compensation circuit, wherein the start circuit ensures that the high-order temperature compensation band gap reference circuit works normally, the bipolar band gap reference circuit generates a band gap reference voltage of a low temperature coefficient, and a temperature segmental linear compensation voltage generated by the segmental linear temperature compensation circuit and a delta VGS temperature compensation voltage generated by the delta VGS temperature compensation circuit are added into the low-temperature coefficient band gap reference voltage generated by the bipolar band gap reference circuit, so that a high-order temperature compensation reference voltage is obtained, and the temperature coefficient of a band gap reference circuit output voltage is greatly decreased.

The invention provides a high-order temperature compensation band-gap reference circuit free of bipolar transistors. The high-order temperature compensation band-gap reference circuit free of the bipolar transistors comprises a front adjuster circuit, a first-order band-gap reference circuit, a low-temperature zone temperature sectional compensation circuit, a high-temperature zone temperature sectional compensation circuit and a starting circuit; a first-order band-gap reference voltage is obtained by adopting a negative-temperature-coefficient voltage VCTAT produced by a grid-source voltage of a sub-threshold NMOS (N-channel metal oxide semiconductor) transistor and a positive-temperature-coefficient voltage VPTAT produced by difference between grid-source voltages of two sub-threshold NMOS transistors, low-temperature zone temperature sectional compensation voltages (VNL1 and VNL2) and high-temperature zone temperature sectional compensation voltages (VNL3 and VNL4) are introduced into the first-order band-gap reference voltage produced by the first-order band-gap reference circuit, a band-gap reference voltage with low temperature coefficient is obtained, and a power supply rejection ratio of band-gap reference is increased with a front adjuster technology, so that the high-order temperature compensation band-gap reference circuit free of the bipolar transistors is obtained.

The invention discloses a frequency detection principle-based two-axis resonant silicon micro-accelerometer, which consists of an upper layer and a lower layer. The upper layer is an accelerometer mechanical structure manufactured on a monocrystalline silicon slice; the lower layer is a signal lead manufactured on a glass substrate; the accelerometer mechanical structure consists of a mass block, an outer frame, two pairs of identical resonators and eight identical first-stage lever amplification mechanisms; the mass block is positioned in the middle of the structure; one pair of resonators is symmetrically arranged on the upper and lower sides of the mass block and is used for measuring acceleration input along a y axis; the other pair of resonators is symmetrically arranged on the left and right sides of the mass block and is used for measuring acceleration input along an x axis; and the whole structure is centrosymmetric. The micro-accelerometer is not required to be supported by a supporting beam, so that the structure is simplified; and the micro-accelerometer has a stable structure, and inertia force converted from the acceleration is effectively transferred to the resonators simultaneously.

The invention discloses a CMOS subthreshold high-order temperature compensation bandgap reference circuit comprising a current mould bandgap reference circuit and a feedback control loop, wherein the current mould bandgap reference circuit comprises six PMOS pipes, four NMOS pipes and five resistors, and the feedback control loop comprises two PMOS pipes and four NMOS pipes. The invention has lower temperature coefficient and higher power supply suppression ratio. By adopting a CMOS technology library with a CSMC0.5mum standard, the obtained temperature coefficient temperature coefficient is after simulation only 0.42ppm / DEG C, and the PSRR under low frequency reaches more than 78dB.

The invention provides a power detection circuit and method. The power detection circuit comprises a power supply switching module which is switched on or switched off according to power-on or brown-out condition; a voltage division sampling module for sampling a power supply voltage; a voltage comparison module for carrying out power-on detection; a brown-out detection module for carrying out brown-out detection; and a pulse latching module for latching a voltage rising edge transmitted by the voltage comparison module and a low level transmitted by the brown-out detection module. The methodcomprises the steps of switching on the power supply voltage, carrying out voltage division sampling on the power supply voltage and carrying out power-on detection on a signal obtained through voltage division sampling; carrying out power-on detection on the power supply voltage; outputting a first logic level if the power-on is finished, and carrying out delayed output to ensure that a system works stably; and outputting a second logic level if the brown-out occurs. The power detection circuit and method have a power-on detection function; after the power-on is finished, no power consumptionexists; and the detection precision of the power detection circuit and method is far higher than that of the prior art.

The invention relates to a self-calibrating method of internal reference resistors of a multi-range digital electronic measuring instrument, comprising the following steps of: on the basis of the design line of the traditional digital electronic measuring instrument, additionally setting an electronic switch and a self-calibrating program; setting a resistor with good long-term stability as an internal standard resistor in a set of internal reference resistors; when in a self-calibrating state, controlling the electronic switch by using the self-calibrating program to form different combinations so as to obtain comparing and measuring circuits among different reference resistors; and respectively and directly or indirectly comparing the reference resistors with the set internal standard resistor to measure respective actual resistance values and storing the actual resistance values in an internal storage for automatically correcting measuring results. Because only one standard resistor with good long-term stability needs to be adopted, other reference resistors are compared and calibrated with the standard resistor, and the method effectively reduces the requirements of other reference resistors, is beneficial to reducing the production cost and ensuring the measuring precision of each measuring process so that the calibration in the production process and the periodic calibration of users both are simpler and more effective and accurate.

The invention discloses a silicon micro-resonant accelerometer which comprises an upper layer and a lower layer, wherein the upper layer is an accelerometer mechanical structure manufactured on a single-crystal silicon wafer, the lower layer is a signal lead manufactured on a glass substrate, the accelerometer mechanical structure comprises a mass block, an outer frame, two resonators, four primary leverage amplification mechanisms, two rigid rods and two guide mechanisms, a first resonator and a second resonator are symmetrically arranged at the upper side and the lower side of the mass block, one end of either resonator is connected with the outer frame, and the other end is connected with the guide mechanism; and the mass block is connected with the outer frame by four multi-folded beams, and the outer frame enables the mechanical structure part at the upper layer to suspend above the glass substrate part at the lower part by means of four fixed bases which are symmetrical with the center of the mass block. The invention greatly reduces the influence of residual machining stress and heat stress produced by the temperature change of the working environment on the vibration frequency of the structure, improves the stability of the resonant frequency of the resonator and reduces the temperature coefficient of frequency.

The invention provides a method and a device for selecting a magnetic levitation driven needle. A pattern bit, a needle jack, a needle and a triangle in a traditional weaving structure are integrated together. In an action process, an impact friction and a lateral force do not exist between the needle and a needle shell base, thereby realizing a high-speed and magnetic levitation controlled needle three-position motion. The device for selecting the magnetic levitation driven needle has the advantages that the structure is simple, the cost is low, the service life is long, and the like.

The invention discloses a heat tube type photovoltaic photo-thermal member which comprises a glass cover plate, solar battery pieces, a packaging material TPT, a solar spectrum selective absorption coating, a tube plate type heat absorption plate, a heat insulation layer and an outer section frame, wherein the solar battery pieces are in series connection and parallel connection in rows, and the solar spectrum selective absorption coating is used for absorbing the infrared wave band of the solar spectrum; the glass cover plate, the solar battery pieces, the TPT packaging material and the solar spectrum selective absorption coating are sequentially laminated and attached from top to bottom; the tube plate type heat absorption plate is mainly formed by a plate body and a heat collection tube arranged on the lower surface of the plate body, the cross section of the heat collection tube is of a downwards protruding arc shape; the upper surface of the plate body is fixed on the lower surface of the solar spectrum selective absorption coating to form a strong platy body; the heat insulation layer covers the lower surface of the tube plate type heat absorption plate and is supported by a base plate, and the heat insulation layer and the strong platy body are jointly fixed in the outer section frame. By the adoption of the heat tube type photovoltaic photo-thermal member, an air interlayer is decreased, and therefore heat conversion efficiency is enhanced; in addition, because the heat collection tube is of the arc shape, the contact area can be enlarged, pressure-bearing can be enhanced, and it can be guaranteed that the member runs stably for a long time.

The invention discloses a lower-power-consumption reference source circuit. The lower-power-consumption reference source circuit comprises a starting circuit unit, a current generation circuit unit and an output load circuit unit, wherein the starting circuit unit, the current generation circuit unit and the output load circuit unit are connected in sequence, the starting circuit unit is used for providing starting voltage, and preventing operation in a zero state area, the current generation circuit unit is used for generating microcurrent for the output load circuit unit, and reducing power consumption of the lower-power-consumption reference source circuit, and the output load circuit unit is used for achieving output of a zero-temperature coefficient and low-output voltage. The lower-power-consumption reference source circuit has the advantages of being low in power consumption, low in temperature coefficient, large in range of operating voltage and small in area.

The invention provides an input undervoltage protecting circuit of a switching power supply controller. The input undervoltage protecting circuit of the switching power supply controller comprises a current detection circuit, a reference voltage generating circuit, an undervoltage protecting signal generating circuit and a pulse outputting control circuit. The current detection circuit comprises a controller internal resistor R2 and a controller external resistor R1, and the resistance value of the R2 is far smaller than that of the R1. The reference voltage generating circuit comprises an internal resistor R3 and a reference current source Iref, and the R3 and the R2 are resistors of the same type in the controller. The undervoltage protecting signal generating circuit comprises a comparator comp. A protecting point input voltage Vin(p) meets the formula (please see the formula in the specification). When the input voltage Vin of a switching power supply drops to be lower than the protecting point input voltage Vin(p), the output end UVP of the comparator comp generates undervoltage protecting signals to control the pulse outputting control circuit to cut off pulse output of GATE pins of the controller. According to the input undervoltage protecting circuit of the switching power supply controller, the peripheral circuits of the controller are simplified, the loss is small, meanwhile, the precision of input undervoltage protecting is high, and process bias is small. The invention further provides an input undervoltage protecting circuit with feed-forward compensation, the feed-forward compensation current Icom is in proportion to input voltages, the precision is high, and the process bias is small.

The invention discloses a nonresistance CMOS (Complementary Metal-Oxide-Semiconductor Transistor) voltage reference source, which comprises a start-up circuit, a bias circuit, a nonresistance PTAT voltage generating circuit, a CTAT voltage generating circuit, and a stacking output voltage circuit. The voltage reference source provided by the invention calculates the sum of first order positive temperature compensation voltage and first order negative temperature compensation voltage generated by the nonresistance PTAT voltage generating circuit and the CTAT voltage generating circuit, and outputs compensated zero temperature voltage, which has favorable temperature stability and higher power rejection ratio. The voltage reference source provided by the invention can be applied in various kinds of analog and digital-analog mixed integral circuit, such as various kinds of oscillators, phase-locked loops, data converters, etc.

The invention provides a power supply voltage electrification detection circuit and an achieving method for electrification detection. The power supply voltage electrification detection circuit at least comprises a power supply voltage detection circuit, a voltage comparator circuit and a level conversion circuit, wherein the voltage comparator circuit is connected with the power supply voltage detection circuit; the level conversion circuit is connected with the voltage comparator circuit. By adopting the power supply voltage electrification detection circuit provided by the invention, shaking and turnover phenomena of output voltage are avoided, and meanwhile the driving property of circuit output voltage is effectively improved; the power supply voltage electrification detection circuit is small in threshold variation along with temperature and has the characteristics of high precision and low temperature coefficient; the structure is simple, the power consumption is small, the complexity of a conventional circuit is effectively reduced, and the power consumption of the circuit is reduced. The achieving method of electrification detection on power supply voltage electrification detection circuit is simple and rapid in electrification speed detection, the detection efficiency is effectively improved, and meanwhile, the problem that the precision is low as the threshed voltage of the power supply voltage electrification detection circuit can be solved.

There is provided a chip resistor including a ceramic substrate; a first resistance layer formed on the ceramic substrate and including a first conductive metal and a first glass; and a second resistance layer formed on the first resistance layer, including a second conductive metal and a second glass, and having a smaller content of glass than the first resistance layer, thereby obtaining relatively low resistance and a relatively small temperature coefficient of resistance (TCR).

The present invention discloses one kind of ferrite material with low temperature coefficient, low loss and high saturated flux density and its preparation process. It is mainly spinel type structure and consists of Fe2O3 45-52 mol%, ZnO 20-35 mol%, CuO 5-15 mol%, MnO 1-3 mol%, and NiO 10-18 mol%. The preparation process includes the following steps: mixing material; pre-sintering; adding impurity; secondary ball milling; forming and sintering. The ferrite material has CuO and Mn3O4 to replace NiO and thus lowered material cost, lower pre-sintering temperature and sintering temperature and thus low power consumption, low requirement in sintering apparatus and low production cost; relatively wide pre-sintering temperature range and sintering temperature range, no need of protecting atmosphere, high technological repeatability and product consistency.

A dielectric substance is laminated on one surface of a piezoelectric substance, and an IDT and reflectors are disposed as electrodes at a boundary between the piezoelectric substance and the dielectric substance, and the thickness of the electrodes is determined so that the acoustic velocity of the Stoneley wave is decreased less than that of a slow transverse wave propagating through the dielectric substance and that of a slow transverse wave propagating through the piezoelectric substance, thereby forming a boundary acoustic wave device.

The invention discloses a method for producing a soft magnetic ferrite core. The method comprises the following steps of: mixing of raw materials, pre-sintering, ball milling, compression moulding, secondary sintering, grinding and detection, wherein an integral magnetic-attraction double-sided grinding machine is adopted in the grinding process. The magnetic core produced by the method has high magnetic conductivity and low loss factor, and energy sources can be saved; the magnetic core has uniform color, flat end surface and bright and clean surface; the ball milling as well as the uniformity and sphericity of the mixed material are improved; a low-temperature sintering technology is adopted, the heating rate and cooling rate of each stage are adjusted, the ferrite transformation of the material is promoted, and the grain size can be effectively controlled; and the initial permeability and temperature characteristic are improved.

The invention discloses a constant temperature measurement-type micro humidity sensor and a producing method thereof, relating to the sensor technology; the sensor consists of a humidity sensitive film capacitor and a pedestal, wherein at least one electrode in the lower electrode of the humidity sensitive film capacitor acts as a capacitance or impedance measuring electrode and a constant temperature-control heating electrode and works with a temperature sensor in the lower electrode under the control of an external circuit of the sensor to cause the micro humidity sensor to measure humidityat certain constant temperature. A thin supporting film for supporting the humidity sensitive film capacitor in the sensor has through holes or clearance structures, thereby reducing heat loss and causing the sensor to realize constant temperature measurement under relatively low power consumption. The micro humidity sensor is not affected by the environmental temperature, has small temperature coefficient and good low-temperature performance, realizes the humidity measurement at negative temperatures and has a volume smaller than 2mm*2mm*2mm. The invention is applied to daily life, industrial production, weather forecast, environment monitoring, aeronautics, astronautics and other fields.

The invention provides a bandgap reference circuit with a high power supply rejection ratio and high order curvature compensation. The bandgap reference circuit comprises a starting circuit, a forward-acting regulator circuit, a bandgap circuit, a low temperature area piecewise linear temperature compensation circuit, a temperature compensation circuit with a high temperature area and the absolute temperature T1.5 in direct proportion and a high temperature area piecewise linear temperature compensation circuit. A low temperature area piecewise linear temperature compensation current and a temperature compensation current with the high temperature area and the absolute temperature T1.5 in direct proportion are added in a traditional bandgap reference circuit, a high temperature area piecewise linear temperature compensation current is drawn out of the traditional bandgap reference circuit, and accordingly the reference circuit with the high order curvature compensation is obtained; a negative feedback forward-acting regulator technology is added into reference voltage with high order curvature compensation, and accordingly the bandgap reference circuit with the high power supply rejection ratio and the high order curvature compensation is obtained.

The invention discloses a neodymium iron boron magnet, a preparation method and a device applying the same, belonging to the field of magnetic materials. The magnet comprises the following components in percentage by weight according to the general formula: 27 to 35 percent of R representing one or two rare-earth elements except Gd, 0.55 to 2 percent of Gd, 0.5 to 3.5 percent of Co, 0.05 to 0.5 percent of M1 representing one transition metal element such as Cu, Al or Ge, 0 to 0.5 percent of M2 being one or two transition metal elements except Co and M1, 0.9 to 1.2 percent of B (namely boron) and the balance of Fe and unavoidable impurities. The neodymium iron boron magnet disclosed by the invention is compounded with Gd, Co, M1 and M2, thus the reversible magnetic induction temperature coefficient alpha and the coercive force temperature coefficient beta are better improved, the coercive force of the magnet is greatly improved while the magnetic energy product and residual magnetism are guaranteed not to reduce, the heavy rare earth element Gd is effectively utilized, and the performance is improved while the manufacturing cost is well saved.

The invention discloses a voltage reference source capable of compensating in a full-temperature range, which particularly comprises a start-up circuit, a first-order temperature-compensation circuit, a proportional superposition output circuit and a current bias circuit, and is characterized by further comprising a low-temperature high-order compensation circuit, a high-temperature high-order compensation circuit and a negative feedback circuit. The voltage reference source adopts index curvature compensation at the low temperature, adopts piecewise linear curvature compensation at the high temperature, has extremely good temperature stability and extremely low temperature coefficient and can be applied to an analogue integrated circuit, a high-precision digital-to-analogue conversion circuit and a pure digital integrated circuit.

The invention discloses a method for charging a battery of an electric road vehicle. The method comprises the following steps of: (1) pre-charging; (2) A-period constant current charging; (3) B-period constant current charging; (4) constant voltage charging; (5) double-threshold charging; and (6) float charging, wherein the base number of the charging environment temperature is 25 DEG C, current and voltage in the whole charging process are adjusted in inverse proportion to the environment temperature, a current adjustment coefficient is 30 to 80 mA / DEG C, a voltage adjustment coefficient in the step (6) is 3 to 4 mV / monomer.DEG C, and a voltage adjustment coefficient in other steps is 5 to 6 mV / monomer.DEG C. By adjusting charging parameters under different temperature conditions, a charging effect of the battery at different temperatures is ensured, and the service life of the battery is prolonged.

The invention discloses a bandgap reference circuit employing a current subtraction technology. Temperature compensation is realized by the current subtraction technology. The bandgap reference circuit comprises two current generating circuits with CTAT (Complementary To Absolute Temperature) and a current subtraction circuit, wherein each of the current generating circuits with the CTAT consists of two P-channel metal oxide semiconductor (PMOS) pipes, an operation amplifier (OPA), a resistor and a triode; and the current subtraction circuit consists of two PMOS pipes, two N-channel metal oxide semiconductor (NMOS) pipes and a resistor. The circuit acquires relatively stable bandgap reference through current subtraction of the two current generating circuits with the CTAT, and has the advantages of low temperature coefficient, low needed supply voltage (less than 1V) and the like.