52 results about "Input offset voltage" patented technology

The invention discloses a low-output-ripple ultralow-offset-voltage operational amplifier and a working method thereof. The low-output-ripple ultralow-offset-voltage operational amplifier comprises a first chopper circuit, a first-stage operational amplifier additionally provided with an offset voltage adjusting circuit, a second chopper circuit, a notch filter, a second-stage operational amplifier and a third-stage operational amplifier which are sequentially connected. The offset voltage adjusting circuit trims the input offset voltage of the first-stage operational amplifier to hundreds of microvolts and then outputs the offset voltage to the second chopper circuit; the first chopper circuit and the second chopper circuit are used for modulating the offset voltage of the first-stage operational amplifier to a chopping frequency, and then the ripple voltage at the chopping frequency is filtered by the notch filter; the first-stage operational amplifier is designed to be a high-gain amplifier so as to restrain input offset voltage errors caused by the second-stage operational amplifier and the third-stage operational amplifier. According to the invention, low output ripple voltage and ultralow input offset voltage can be realized only by using the wave trap with a small area.

The invention discloses a foreground calibration circuit for an input offset voltage of an SAR ADC comparator. The foreground calibration circuit comprises a power supply input circuit, an input geminate transistor circuit, a latch comparator, an SAR successive approximation register and a Res DAC resistance voltage division type digital-to-analog converter. The output end of the power input circuit is electrically connected with the power end of the input geminate transistor circuit; an analog input signal VIN and a reference voltage signal VREF are input into the input end of the input geminate transistor circuit, and the output end of the input geminate transistor circuit is electrically connected with two input ends of the latch comparator; the two output ends of the latch comparator are electrically connected with the input end of the SAR successive approximation register, and the output end of the SAR successive approximation register is electrically connected with the input end of the Res DAC resistance voltage division type digital-to-analog converter; the output end of the Res DAC resistance voltage division type digital-to-analog converter outputs a CALIP signal and a CALIN signal to a grid electrode of an adjusting tube in the input geminate transistor circuit, so that the adjusting tube generates compensation current to compensate the current difference of two input geminate transistors in the input geminate transistor circuit, and offset voltage is calibrated.

The invention relates to an audio decoding output stage circuit and audio equipment, the audio decoding output stage circuit comprises an I / V conversion module and a low-pass filtering module, and the I / V conversion module comprises a conversion circuit, a crossed diamond amplification circuit, an overcurrent protection circuit and a Roche network circuit; the conversion circuit comprises a JFET (Junction Field Effect Transistor) audio operational amplifier chip and an I / V (Input / Output) conversion resistor and is used for converting an input current into an analog voltage signal; the crossed diamond amplifying circuit can reduce the input offset voltage; the over-current protection circuit can carry out over-current protection; the rowbell network circuit can prevent high-frequency self-oscillation of the power output stage; and the low-pass filtering module comprises a filtering circuit and an ultrahigh frequency filtering circuit arranged at the output end of the audio decoding output stage circuit. The scheme can bring high-performance sound performance, and has the advantages of lower distortion, higher conversion rate, low output impedance and large pushing current.

The present invention relates to an input offset voltage automatic correction circuit, the correction circuit includes a comparator circuit, a comparator circuit output drive tube, a switch control tube, and a logic control module; wherein the comparator circuit includes a first-level input and a second-level input, the correction circuit also includes a first-level input load and a second-level input load, the first-level input is connected to the first-level input load, the second-level input is connected to the second-level load, and the switch control tube controls the comparison circuit; the technical solution has a simple structure, and automatic correction can be achieved by adding conventional components. The circuit of the present invention will re-correct the input offset voltage every time it is powered on, eliminating the influence of the external environment on the input offset voltage, and the technical solution automatically reduces the input offset voltage of the comparator to a very low level.

This application relates to the field of operational amplifier circuit technology, and more particularly to an inverting operational amplifier circuit for eliminating input offset voltage. It includes an input resistor for receiving an input voltage; an operational amplifier for inverting and amplifying the input voltage; an output resistor section connected in series between the output terminal of the operational amplifier and the input resistor, the output resistor section being composed of multiple output resistors connected in series; multiple current sources connected to nodes between the various output resistors of the output resistor section, the current sources being used to compensate for the output offset voltage caused by the input offset voltage of the operational amplifier; and a digital code input section for adjusting the current values ​​of the current sources; wherein the voltage value of the output offset voltage is determined based on the current values ​​of the multiple current sources and the corresponding resistance values ​​of the output resistor section. Using this application is advantageous for canceling the output offset voltage caused by the input offset voltage of the operational amplifier and appearing at the output terminal.

This invention discloses a bandgap reference circuit structure, belonging to the field of integrated circuit design technology. The circuit structure includes a bandgap reference core circuit, a chopper-equipped operational amplifier (op-amp), a bandgap reference startup circuit, a temperature-to-absolute-temperature (PTAT) bias current source, and a current source startup circuit. By optimizing the bandgap reference core circuit architecture, combining chopper technology to eliminate the effects of offset voltage and device mismatch, and with the matching startup circuit and low-voltage-adaptive bias current source, the reference voltage is essentially independent of the op-amp input offset voltage, improving circuit symmetry performance and load dynamic response speed. Furthermore, in most common complementary metal-oxide-semiconductor (CMOS) processes, it only requires a power supply voltage of 2V or higher to operate stably, significantly improving the accuracy and stability of the reference voltage.

The present invention discloses a memristor simulator equivalent circuit, control method and electronic device, belonging to the technical field of circuit element simulators. The memristor simulator equivalent circuit provided by the present invention utilizes a combination of a multiplier and an operational amplifier to reproduce the characteristics of a memristor and replace the memristor for use. It not only supports long-term debugging and use, but also avoids the use of complex hardware circuit design and high device costs, and solves the problem of performance degradation under non-ideal conditions. By introducing an integrator composed of a second operational amplifier and an integrating capacitor, the dynamic characteristics of the memristor can be accurately simulated, ensuring the stability of the conductivity in the non-conducting state and reducing errors caused by the non-ideal characteristics of the operational amplifier (such as input offset voltage and input bias current); by providing a single-pole double-throw switch, the circuit can be flexibly switched between different operating modes, making it easy to adjust the circuit parameters according to actual application requirements, thereby optimizing the simulator performance.

The invention relates to the technical field of operational amplification circuits, in particular to an inverted operational amplification circuit for eliminating input offset voltage. The input resistor is used for receiving an input voltage; the operational amplifier is used for outputting the input voltage after inverting amplification; the output resistor part is connected between the output end of the operational amplifier and the input resistor in series, and the output resistor part is formed by connecting a plurality of output resistors in series; a plurality of current sources respectively connected to nodes between output resistors of the output resistor unit, the current sources compensating an output offset voltage caused by an input offset voltage of the operational amplifier; the digital code input part is used for adjusting the current value of the current source; wherein the voltage value of the output offset voltage is determined according to the respective current values of the plurality of current sources and the resistance value corresponding to the output resistance part. According to the invention, the offset of the output offset voltage caused by the input offset voltage of the operational amplifier and appearing at the output end is facilitated.

The invention provides a current proportion mirror image circuit and an electronic product. The current proportion mirror image circuit comprises a current mirror module composed of a first transistor, a second transistor, a third transistor, a first capacitor, an operational amplifier and a mode switching unit; wherein the first ends of the first and second transistors are connected with working voltage, the control ends are connected with driving voltage, and the second end of the third transistor is connected with a CS end; the mode switching unit is used for switching an input signal of the operational amplifier and a control end signal of the third transistor based on different working modes; the second end of the third transistor outputs detection current having a preset proportion with the load current, and the second end of the second transistor is connected with a load; and the offset compensation module is used for sampling and compensating the input offset voltage of the operational amplifier. The offset compensation module is constructed by utilizing a self-zero-setting technology, so that the input offset voltage of the operational amplifier in the current mirror module is reduced, and the detection precision of the current proportion mirror circuit is improved.

The invention provides a temperature sensor, a circuit system and electronic equipment, and the system comprises a temperature voltage generation module which is used for temperature detection voltage; the temperature voltage comparator is used for comparing a first voltage and an analog voltage and outputting a comparison result signal, and the first voltage is equal to the sum of the temperature detection voltage and the input offset voltage of the temperature voltage comparator; the input offset voltage and the temperature detection voltage are both in direct proportion to the temperature to be detected, the load capacitance ratio of the input offset voltage and the temperature voltage comparator is in a logarithmic linear relation, and input geminate transistors in the temperature voltage comparator work in a sub-threshold region; the N-bit logic control module is used for outputting a corresponding temperature detection digital signal according to the comparison result signal; and the N-bit digital-to-analog conversion module is used for outputting a corresponding analog voltage according to the temperature detection digital signal, the temperature detection digital signal after N times of comparison is used for representing a first voltage, and the first voltage is used for representing the temperature to be detected.

To provide an input circuit that can reduce an input offset voltage while suppressing a change in response of a semiconductor device, and a semiconductor device comprising such an input circuit.SOLUTION: An input circuit has a first differential transistor portion having a plurality of first transistors connected in parallel to each other, a second differential transistor portion having a plurality of second transistors connected in parallel to each other, and a cutoff selectable portion. An output circuit has a first current path portion and a second current path portion disposed in parallel to each other. A first terminal of each of the plurality of first transistors is connected to the first current path portion. A first terminal of each of the plurality of second transistors is connected to the second current path portion. The cutoff selectable portion is connected in series to at least one transistor among the plurality of first transistors and the plurality of second transistors. The cutoff selectable portion is selected to be in one of a state that allows a current to flow and a state that cuts off the current.SELECTED DRAWING: Figure 1

The invention belongs to the field of analog integrated circuits, and particularly relates to a low-noise operational amplifier with a wide common-mode input range. The amplifier comprises an input bias current adjusting unit, a differential input stage unit, an intermediate gain stage unit and a buffer output stage unit which are connected in sequence, the input bias current adjusting unit is used for sampling input-stage current and adjusting the magnitude and temperature drift of input bias current; the differential input stage unit is used for signal acquisition and adopts a rail-to-rail input type common-emitter common-base differential pair structure; the intermediate gain stage unit amplifies a signal received by the differential input stage unit, and the buffer output stage unit provides enough output current to ensure the current driving capability of the operational amplifier; according to the operational amplifier, the equivalent input voltage noise can be reduced by controlling the working current of the input geminate transistors and the load resistance, the operational amplifier can be ensured to have low input offset voltage by trimming the load resistance, and the requirements of the operational amplifier in low-noise and high-precision application scenes are met.

The present invention relates to a low-voltage operational amplifier for reducing system offset voltage, comprising a folded cascode input module (101), a CLASS_AB output stage control circuit (102), and an output stage module (103). The low-voltage operational amplifier solves the problems of large system offset voltage, inaccurate output stage quiescent current control, and wasted dynamic power consumption in existing low-voltage CLASS_AB operational amplifiers, improves the output stage quiescent current error caused by the channel length modulation effect, and simultaneously improves the current matching of the first stage cascode tube by adding a second stage cascode tube, effectively reducing the input offset voltage of the operational amplifier system. When a large external source / sink current exists, the CLASS_AB output stage control circuit (102) is current-limited to limit the internal maximum power consumption, thereby reducing both heat generation and useless power consumption, thereby broadening the application of the CLASS_AB output stage operational amplifier in low-voltage, high-precision circuit systems.

The invention relates to the technical field of analog integrated circuits, in particular to a high-precision temperature sensor temperature-sensing front-end circuit based on a chopping technology, and aims to solve the problems of low-frequency 1 / f noise, operational amplifier input offset voltage drift, band-gap reference temperature drift, limited output driving capability and the like existing at the front end of a traditional temperature sensor. The front-end circuit comprises a chopping band-gap reference source circuit, a chopping buffer circuit and a two-phase non-overlapping clock generation circuit, wherein the chopping band-gap reference source circuit adopts a parasitic bipolar PNP transistor with an emitter junction area ratio of 8: 1 as a temperature sensing device, and a high-gain chopping folded cascode operational amplifier is embedded in the chopping band-gap reference source circuit; and stable positive temperature coefficient voltage and low-temperature drift reference voltage are generated. Noise and maladjustment are inhibited from the system architecture level, the temperature measurement precision can reach the sub-degree centigrade level, the loading capacity is high, the method is achieved based on the standard CMOS technology, a special technology and complex temperature calibration are not needed, and the method has the advantages of being low in cost, high in stability and large-scale integration.

The application relates to a full common-mode range offset voltage trimming operational amplifier, relates to integrated circuit technology, and comprises an operational amplifier circuit and a trimming circuit, characterized in that the trimming circuit comprises a first current source (101) to a seventh current source (107), and a fifteenth NMOS tube (M15) to a thirtieth PMOS tube (M30), a current output end of a sixth current source (106) is connected with a current input end of the seventh current source (107), and a gate is connected with a positive level input line. The application can correct the full common-mode range offset voltage of a rail-to-rail input operational amplifier to a target value, and the input offset voltage almost does not change with the change of a common-mode voltage, so that the linearity of the full common-mode range of the operational amplifier is improved.

The invention relates to a construction method and device of a reliability prediction model of a bipolar operational amplifier, computer equipment, a computer readable storage medium and a computer program product. The method comprises the following steps: carrying out a constant stress accelerated life test on a transistor to obtain change relation data of a normalized beta value at any time length, carrying out parameter fitting on the change relation data to obtain an accelerated degradation coefficient, a time power coefficient and an undetermined coefficient of the transistor, and establishing a degradation track model of the transistor, establishing a circuit simulation model of a differential input structure, and performing an orthogonal test to obtain influence data of a normalized beta value on the input offset voltage of the bipolar operational amplifier; establishing a mapping relation between the normalized beta value and the input offset voltage of the bipolar operational amplifier according to the influence data; and establishing a reliability prediction model of the bipolar operational amplifier by using the degradation track model and the mapping relation. By adopting the method, the reliability prediction accuracy and efficiency of the bipolar operational amplifier can be improved.

The invention provides an operational amplifier and a chip, and belongs to the technical field of operational amplifiers. The operational amplifier comprises an operational amplification circuit, an offset correction circuit and a control circuit, wherein the control circuit controls the operational amplification circuit and the offset correction circuit to work in a periodic mode. In each working period, the control circuit controls the operational amplifier circuit to generate an output voltage according to the input voltage and the first common-mode voltage; meanwhile, the control circuit controls the offset correction circuit to carry out zero clearing on the offset voltage of the offset correction circuit and carries out zero clearing on the target offset voltage under the action of the output voltage and the second common-mode voltage, and the target offset voltage is a part of the first offset voltage corresponding to the operational amplifier circuit. According to the operational amplifier, loop oscillation can be effectively suppressed and corrected, the output overshoot of the operational amplifier circuit can be remarkably reduced, the residual offset voltage of the operational amplifier circuit can be weakened cycle by cycle, and the input offset voltage of the operational amplifier circuit continuously approaches zero.

The present application relates to a method, device, computer equipment, computer-readable storage medium and computer program product for constructing a reliability prediction model of a bipolar operational amplifier. The method includes: conducting a constant stress accelerated life test on a transistor to obtain data on the variation relationship of the normalized β value with time duration, performing parameter fitting on the variation relationship data to obtain the acceleration degradation coefficient, time power coefficient and undetermined coefficient of the transistor, and establishing a degradation trajectory model of the transistor; establishing a circuit simulation model of a differential input structure, and obtaining, through orthogonal experiments, data on the influence of the normalized β value on the input offset voltage of the bipolar operational amplifier; establishing a mapping relationship between the normalized β value and the input offset voltage of the bipolar operational amplifier according to the influence data; and establishing a reliability prediction model of the bipolar operational amplifier by using the degradation trajectory model and the mapping relationship. The use of this method can improve the accuracy and efficiency of the reliability prediction of the bipolar operational amplifier.

The invention provides a low-cost switching power supply for high-precision electric energy metering and a control method thereof. A voltage output pin of a switching power supply chip is grounded through a first capacitor; an external low-voltage power supply is connected and charges the first capacitor through the first resistor and the first diode, and the maximum soft start current of the boost power supply circuit is limited to be less than 100mA by setting the resistance value of the first resistor; an external low-voltage power supply is connected to a power supply input pin of the switching power supply chip through a sampling resistor, the sampling resistor is connected with an in-phase input end and an inverted input end of a voltage comparator, and whether overcurrent occurs or not is judged according to high or low level signals output by the voltage comparator; the over-current protection threshold value of the USB power supply circuit is limited by setting the resistance tolerance level and the input offset voltage of the voltage comparator. By designing the soft start and overcurrent protection circuit, the USB power supply with surge current prevention and precise overcurrent protection functions is provided, and the effects of greatly reducing the cost, simplifying the circuit design and improving the circuit reliability are achieved.

This invention provides a low-dropout linear regulator, including a base regulator circuit, a switching unit, and a load. One end of the load is connected to the output terminal of the base regulator circuit, and the other end of the load is connected to load ground. The switching unit is connected to the base regulator circuit. The switching unit is used to store an offset voltage and a reference voltage at a first input terminal of the base regulator circuit, and then swap the functions of the first and second input terminals of the base regulator circuit to cancel the offset voltage at the first input terminal, thereby reducing the impact of the input offset voltage. This invention also provides a control method for the low-dropout linear regulator.

The invention provides a multi-amplifier circuit. The first amplifier (1) amplifies and outputs two input differential voltages. The second amplifier (2) amplifies and outputs the differential voltages of the two inputs. Each of the first amplifier (1) and the second amplifier (2) includes a first differential input circuit (D1), a second differential input circuit (D2), and a current adjustment unit (30). The first differential input circuit (D1) includes a transistor pair that amplifies and outputs a differential voltage of two inputs. The second differential input circuit (D2) includes a transistor pair that amplifies and outputs a differential voltage input to the two differential input circuits (D1). The differential input circuits (D1, D2) have asymmetric structures that each generate input offset voltages that are positively and negatively opposite to each other. A monitor amplifier (51) amplifies and outputs a differential voltage between an input to the first amplifier (1) and an input to the second amplifier (2). The current adjustment unit (30) adjusts the current ratio of the currents flowing into the differential input circuits (D1, D2) in response to the output of the monitor amplifier (51).

An enhanced auto-zero circuitry and technique for reducing the effective input offset voltage of an amplifier. The circuitry includes a multi-phase auto-zeroing amplifier circuitry including several capacitor and switch components and a switch controller circuit. The switch controller circuit is configured to provide control signals for controlling the switches, where during a first sub-phase of an auto-zero phase, multiple switches are turned on to store an amplifier input offset coarser compensation charge on the input capacitor, and where during a second sub-phase of the auto-zero phase, at least one switch is turned off before turning on another switch to store an amplifier input offset finer compensation charge on the input capacitor via the first auto-zero capacitor.

The invention discloses a memristor simulator equivalent circuit, a control method and electronic equipment, and belongs to the technical field of circuit element simulators. The memristor simulator equivalent circuit provided by the invention can reproduce the characteristics of the memristor and replace the memristor by using the combination of the multiplier and the operational amplifier, not only supports long-term debugging and use, but also avoids complex hardware circuit design and high device cost use, and solves the problem of performance degradation under non-ideal conditions. By introducing the integrator composed of the second operational amplifier and the integrating capacitor, the dynamic characteristics of the memristor can be accurately simulated, the stability of conductivity in a non-conducting state is ensured, and errors caused by non-ideal characteristics (such as input offset voltage and input bias current) of the operational amplifiers are reduced; by arranging the single-pole double-throw switch, the circuit can be flexibly switched among different working modes, and circuit parameters can be conveniently adjusted according to actual application requirements, so that the performance of the simulator is optimized.

The present invention belongs to the technical field of operational amplifiers, and particularly relates to a fully differential low-offset high-gain operational amplifier. The present invention includes an operational amplifier core and a feedforward common-mode feedback. The operational amplifier core amplifies the differential signal, and the feedforward common-mode feedback circuit stabilizes the common-mode voltage of the input and output. The present invention uses a floating-biased common-gate circuit and a high-gain NPN transistor series resistor as a current mirror, which significantly improves the gain, reduces the input offset voltage, and at the same time has a high output swing and good stability, and is suitable for use in an analog front-end programmable gain circuit.

The invention provides a voltage transmission circuit, a circuit system and electronic equipment, which are used for transmitting a first voltage and outputting a second voltage, and the circuit comprises a maintaining unit, a switch control module and an operational amplifier module, the switch control module controls the first voltage to charge the maintaining unit in the sampling stage, and controls the maintaining voltage of the maintaining unit to be output to the output end of the operational amplifier module in the maintaining stage. According to the virtual disconnection principle of the non-inverting input end and the inverting input end of the operational amplifier module, electric leakage of the maintaining unit is avoided, so that the maintaining voltage is equal to the second voltage. As the in-phase input end of the operational amplifier module is grounded, the input offset voltage of the operational amplifier module is fixed and reduced, so that the second voltage only changes along with the change of the maintaining voltage, and the transmission precision of the voltage transmission circuit to the first voltage is improved; and the cost of circuit trimming for reducing the input offset voltage is also reduced.

The invention belongs to the technical field of power management, and particularly relates to an overcurrent protection circuit for eliminating input imbalance. The circuit comprises an SW sampling module, a reference voltage generation module, a level shift module, an operational amplifier module, a first transmission gate, a second transmission gate, a third transmission gate, a fourth transmission gate and a capacitor, and through multiplexing an operational amplifier circuit, the operational amplifier circuit alternately works between an operational amplifier mode and a comparator mode under the control of a clock; and the input offset voltage is calibrated in real time, so that the over-current detection precision and reliability are improved.

The present invention addresses the problem of holding an input voltage with high precision. An electronic circuit includes: a sample / hold circuit (1) including a switching circuit, a capacitance element, and an output buffer circuit having a zero point calibration function for adjusting an input offset voltage thereof to zero, the output buffer circuit having a terminal of the capacitance element as an input; and a clock generation circuit (4) that outputs a clock signal (CLK) for zero calibration only at a specific timing and causes the output buffer circuit (2a) to perform a zero calibration operation so as to hold the voltage at the input terminal (Vin) in synchronization with the clock signal ([phi] S). According to the present invention, the charge error of the capacitance of the sample / hold circuit due to zero calibration can be suppressed to the minimum, and the input voltage can be held with high precision by the sample / hold circuit.

The embodiment of the invention provides a band-gap reference voltage source and a power supply chip, the band-gap reference voltage source comprises a band-gap reference module, a sampling and holding module and a voltage buffer module, under a sampling phase, the sampling and holding module obtains a reference sampling voltage equal to a reference voltage, and the voltage buffer module obtains an offset sampling voltage; the sampling holding module is used for holding the reference sampling voltage and eliminating the third input offset voltage and the fourth input offset voltage based on the target sampling voltage so as to output a buffer voltage equal to the reference sampling voltage, the sampling holding module keeps the reference sampling voltage equal to the reference voltage under the holding phase, and the voltage buffer module obtains the target sampling voltage; and the first input offset voltage, the second input offset voltage, the third input offset voltage and the fourth input offset voltage are offset based on the offset sampling voltage to output the buffer voltage, so that high precision and low power consumption of the voltage source can be realized, and the suppression capability of load interference can also be improved.

The invention relates to an analog-to-digital conversion method applied to a column-level analog-to-digital converter. The analog-to-digital conversion method comprises the following steps: 1) signal acquisition; 2) sample holding; 3) analog-to-digital conversion; 4) column-level parallel processing; 5) digital output; and 6) data integration. According to the analog-to-digital conversion method applied to the column-level analog-to-digital converter, the dynamic range of a traditional column-level analog-to-digital converter is enlarged, meanwhile, the range of scene illumination detected by a sensor of the column-level analog-to-digital converter is enlarged, details of an image are increased, and finally the quality of the obtained image is improved; the input offset voltage influence and the large noise influence of a comparator are reduced, and the problems that the dynamic range of a conventional monoclinic column-level ADC is small, so that the range of scene illumination detected by a sensor using the column-level ADC is narrow, image details are few, the quality of a finally obtained image is poor, the comparator is a key part in the ADC, and the image quality is poor are solved. However, the problems of the influence of input offset voltage of the comparator and the influence of relatively large noise exist.

A high-precision current acquisition circuit provided by the present invention, the high-precision current acquisition circuit includes: a control module, a first acquisition module, a second acquisition module, and an operational amplifier module; the first acquisition module and the second acquisition module form a mirror acquisition current structure; the second acquisition module includes a second power transistor; the first acquisition module includes N first power transistors, and the sizes of the N first power transistors are different, so that the ratio K value of the size of each first power transistor to the size of the second power transistor is different; wherein, N is a positive integer, and N≥2; the control module is used to select any one of the N first power transistors as the selected power transistor; and is used to control the working states of the second power transistor and the selected power transistor; the control module adjusts the K value by switching different first power transistors as the selected power transistor, so as to weaken the acquisition error caused by the input offset voltage of the operational amplifier and improve the acquisition accuracy.