1. Field of the Invention
The present invention relates to an integrated circuit (IC) for measuring and an electrical measuring apparatus using the IC.
2. Description of the Related Art
Currently, a conventional integrated circuit for measuring includes an analog digital converter (ADC), a micro control unit (MCU), a system memory, and so on. Furthermore, the MCU includes a random access memory (RAM), a central processing unit (CPU) and a programmable interface, etc.
When an integrated circuit is utilized in measuring devices, sensors for measuring pressures or weights are receiving measuring signals. The sensors convert the measuring signals to electrical signals, such as voltage signals or current signals. The electrical signals are converted into digital signals by the analog-to-digital converter of the integrated circuit. And then, the digital signals are computed, processed or further converted by the MCU, and are displayed on an external display. The MCU computes, processes or further converts the signals by an instruction set stored in the system memory. The total and order of the instructions construct a program.
However, in the above utilizations, many of the integrated circuits having an analog-to-digital converter must perform a proofreading process before displaying an accurate measuring value. In the proofreading process, a standard measuring object having standard values is used. A sensor communicates with the standard measuring object to send out a standard signal. The standard signal is converted to a digital signal used as a standard value to be stored in the memory. When the MCU performs a normal measuring program, the standard value is taken out to compute an actual measuring value according to a measuring signal. After the proofreading process, a proofreading coefficient is produced correspondingly. The proofreading coefficient must be stored and can be read by the MCU, so that the MCU can accurately perform a computation or a conversion to obtain an accurate value. Therefore, most of electrical elements require an electrically erasable programmable read-only memory (EEPROM) to store the proofreading coefficient.
However, an additional burner is needed to write the proofreading accurately in the EEPROM. After the step of writing, the EEPROM is taken out from the burner and is communicated with an electrical measuring device of a terminal system to finish the proofreading process.
At present, there may be some better methods for recording the proofreading parameters, and it's not necessary to take the EEPROM out of terminal system product as described above. Referring to FIG. 1, a conventional IC 100 is shown. The IC 100 is connected to a display 115, an EEPROM 105 and a sensor 101. Before performing a measuring program, the IC 100 must perform a proofreading procedure. The proofreading procedure includes the following steps: a first step of directly contacting the sensor 101 with a standard object (not shown), a second step of outputting a standard analogical signal to an ADC 103 by the sensor 101, a third step of outputting a standard digital signal to an MCU 109 by the ADC 103 according to the standard analogical signal, and a fourth step of storing standard parameters into an EEPROM 105 through a serial interface circuit 107 after processed by MCU 109. When the MCU 109 performs any instruction, the MCU 109 must access instruction sets from an erasable programmable read-only memory (EPROM) 111.
After finishing the proofreading procedure, the standard parameters are stored into the EEPROM 105. When a normal measuring procedure is performed, the sensor 101 directly contacts with an object to be measured and outputs a measuring signal to the ADC 103. After a step of transforming, the ADC 103 outputs a digital measuring signal to the MCU 109, and the MCU 109 reads the standard parameters form the EEPROM 105 through the serial interface circuit 107. After a step of computing, the MCU 109 outputs a measuring result to the display 115 through a timing-controller 113. The MCU 109 must compute the measuring result according to the standard parameters stored in the EEPROM 105. The MCU 109 must use the serial interface circuit 107 to access the standard parameters. The EEPROM 105 is externally connected to the IC 100.
The above way of storing the standard parameters into an external memory has an advantage that the EEPROM 105 is easily accessed, but it increases a cost of the whole measuring system. In addition, when the proofreading procedure is performed or the program memory is recorded, terminal system products need two extra voltage source VPP=12 volt and VDD=5.8 volt, except for a normal chip power source.
What is needed is to provide an IC with a simple proofreading procedure, a low cost and having a self-proofreading function.