I. Introduction:
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Electronic motor personnel use pointer three-meter electric meters or digital multimeters (DMM) in maintenance or experiment. In the past, portable digital instrument industry mostly adopted Harris (acquired by Intersil), JRC, Maxim. The digital multiplexed meter-specific analog-to-digital converter (ADC) produced by foreign companies such as Samsung and Telcom (which has been acquired by Microchip) converts the input analog signal into a digital signal for processing. However, the portable digital instrument industry has fewer features, more samples, and a longer product life cycle. Therefore, these foreign integrated circuit manufacturers have no longer designed new digital multiplexed meter-specific A/D converters, and have even exited the market for digital multiplex meter-specific A/D converters. Digital multiplex meter only needs one chip and then add resistors, capacitors, protection components, etc., to complete a product, so the threshold is not high, and the industry pie is so big, so that the price war is the last, and the profit is not as good as consumption. Sex products. For the digital multiplex meter, the dedicated analog-to-digital converter is the core. Most of the portable instrument industry is small in scale. Unlike the American company Fluke, it can open its own DMM chip.
In recent years, the development of integrated circuits has flourished, and several DMM-specific chip suppliers have appeared. There are two architectures in the analog-to-digital converter section, namely Sigma-Delta (Sigma-Delta) and dual-slope integration (Dual Slop). ) for the architecture. This article will introduce the DMM-specific chip of the Hycon HY12P65 Mixed-Signal Microcontroller, which uses a sigma-delta analog-to-digital converter architecture.
Second, portable power meter evolution:
The portable power meter was first pointed to a three-meter meter. This generation of meters has a low unit price, but has low accuracy, low resolution, low functionality, and no input protection.
Since the beginning of the development of integrated circuits, chip vendors have designed analog-to-digital converters, so there are handheld digital range multiplexed meters (Handheld Manual Range Digital Multimeters), using ICL7106, ICL7108, TLC7135, HI-7159A analog digital The converter, in addition to the voltage, resistance, current and other measurements of the pointer three-meter, increases the capacitance, frequency, temperature, and the DMM manufacturer adds the input protection circuit. However, almost all functions must be switched by external circuit. It is necessary to select the gear position manually by using it, which is inconvenient to use.
In order to simplify the operation, chip suppliers have designed DMM-specific analog-to-digital converters, so there are handheld automatic digital-receiving digital meters (Handheld Auto Range Digital Multimeters). These meters use Telcom TC818A, Samsung KAD7001, JRC NJU9210. Analog-to-digital converters usually design all the functions of the DMM on the chip, as long as the resistors and capacitors are added, and the gears are not manually selected in use.
But users have new requirements for high accuracy, high resolution, online connectivity or special features. Therefore, the chip supplier will design a component for the DMM-specific analog front end (such as Maxim's MAX133/MAX134), or combine the analog front end with the MCU (such as Epson's S1C62M20), and the chip will be equipped with MCU to meet new requirements. However, in addition to the voltage, resistance, current and other measurements of the chips of such products, other functional circuits need to be added, which is not ideal.
In order to achieve the above new requirements, Fukang Technology has launched a new generation of DMM-specific chips, such as HY12P65, to solve these problems.
Third, the chip new trend function overview:
In the future, the trend of portable digital instrument industry, in order to stop the price war, must have its own product function planning, such as: smart meter, it must rely on more flexible DMM chip. The new trend is divided into the following items by function:
1. Can draw a switch network
In the past, the DMM-specific chip fixed each function and file bit switch network. The advantage is that it is easy to design, but the flexible switching multi-function network cannot have its own product function plan. The DMM-specific chips introduced in this article all have programmable switch networks. If the domestic portable digital instrument industry has more room for product design.
â–²HY12P65 Analog Switch Network
2. High resolution Σ-Δ analog to digital converter
In the past, DMM-specific chips produced by foreign manufacturers and A/D converters all use double-slope integration as the architecture. The analog-to-digital converter has a slow conversion speed, and the integrated capacitor quality affects the stability of the entire converter. Error; usually the integrated capacitor needs to use better materials such as MPE or MPP, and it is not easy to achieve higher resolution.
Σ-Δ analog digital signal converter, more and more industrial control and advanced instrument use in recent years, its biggest advantage is less peripheral circuits, fast conversion speed, high resolution and accuracy, and less susceptible to power systems For the 50/60 HZ and all effects, the unit price is gradually lower than the dual-slope integral analog-to-digital converter.
3. Digital square root circuit
There are AC signal measurement sections for both voltage and current. In the past, the measurement of AC signal circuits differed according to the accuracy. There are several measurement methods in the AC measurement method classification table. From the AC measurement method classification table and the average response circuit to measure various waveform errors and other analysis tables, it can be seen that the square root (so-called True RMS) is more accurate in AC signal measurement, and it is very important, but it must be added with RMS-specific components. It is the "RMS-DC (Root Mean Square-DC) converter", so the cost is high and it is easy to be ignored by the general user.
Although the rms conversion component can improve measurement accuracy, the peak value of the over-peak factor will exceed the allowable range of the analog circuit input. The DMM dedicated chip described in this paper has a high-precision fast sigma-delta analog-to-digital converter that can perform digital RMS and Inrush Current measurement functions, and with Peak Hold to achieve higher crest factor voltage measurement.
AC measurement method classification table
Average response circuit measures various waveform errors (from Analog Devices.)
4. Low Pass Filter
In some power measurement applications, there may be a surge or other high frequency signal entrained in the signal to be tested, and the high pass signal will be filtered out using a Low Pass Filter. The DMM dedicated chip introduced in this paper changes the OSR (Over-Sampling Ratio) of the analog digital signal converter, and achieves signal low-pass filtering, which is equivalent to filtering the high-frequency signal to make the value more correct.
Low pass filter (from Fluke 289 Users Manual)
Low Pass Active Filter for 10 kHz cutoff (from National Semiconductor Application Note 31)
5. Peak Hold
In some electromechanical applications, it is necessary to measure the peak value of the wave. The peak detection circuit (Peak Hold) is used to lock the voltage. The analog-to-digital converter is performing voltage conversion, but the capacitance of the circuit is easily affected by the external environment. And there have been changes. The DMM dedicated chip introduced in this paper has digital peak detection, which compares the analog digital conversion results to make the values ​​more correct.
Low Drift Peak Detector (from National Semiconductor Application Note 31)
6. Temperature sensor
Portable power measuring devices, sometimes in addition to electrical and component measurements, increase temperature measurement. There are four types of temperature sensors that are most common: Thermocouple, Resistance Temperature Detectors (RTD), Thermistors, and integrated circuits. In the portable power measuring device, the thermocouple measuring structure is mostly used. The principle is that the two metals are connected to each other to generate a Seebeck effect voltage, but the voltage is zero when the temperature to be measured is the same as the ambient temperature. Cold-Junction Compensation must be done for ambient temperature. The DMM dedicated chip described in this article has a temperature sensor.
Temperature Measurement Circuit. (From Texas Instruments OPAx235 Datasheet)
7. Standard serial interface
HY12P65 has UART (Universal Asynchronous Receiver/Transmitter) and SPI (Serial Peripheral Interface) interface. The new generation of portable digital instruments, most of which have UART interface and computer communication functions, can achieve automatic testing and automatic correction of products, reducing manual operation costs. . The product correction value or measurement value can be stored in the memory (EEPROM or FLASH) outside the MCU through the SPI interface.
8. OTP MCU
In addition to the DMM-specific analog front-end line and integrated 8-bit reduced instruction set (RISC) MCU, the HY12P65 is suitable for low- and medium-order digital meters, saving product circuit layout space and making the product size smaller.
Fourth, the reference data:
l HY12P65(DMM Specialized IC Embedded Digital T-RMS) Datasheet
l HY12P (Digital Multimeter) Family User's Guide
l Make Better RMS Measurements with Your DMM, Agilent Application Note 1392
l Op Amp Circuit Collection, National Semiconductor Application Note 31
Fifth, the chip manufacturer:
l Hycon Technology focuses on the measurement and monitoring of analog signals such as temperature, pressure, weight, voltage, current, and power. Mainly provide related chip development in battery management, instrumentation (including medical, metering, temperature...), and industrial control.
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