Abstract :MCP6S2X family is Microchip Technology has introduced a programmable gain amplifier , can be used in multi- channel analog transmission applications , data acquisition , A / D converter drive and signal measurement system. This paper introduces the structure and function MCP6S2X series , and through multi- channel signal acquisition circuit comparison illustrates the main features of the chip . Finally, a MCP6S2X practical circuit . Keywords :MCP6S2X; Programmable Gain Amplifier ; Multichannel Data Acquisition In the actual circuit applications, the analog signal acquisition is an important part. control and sampling a variety of on-site general parameters ( such as temperature , pressure , flow , etc.) , and these parameters for processing. Often more tricky part is the signal acquisition . With the development of microelectronics , digital signal processing in terms of accuracy and speed of speaking, are rising. The remaining question is how easily the analog data acquisition to microprocessors . In many embedded designs, microcontroller or DSP to handle a number of analog signals to complete a control feature or a series of control tasks . These analog signals often need to go through some kind of processing ( such as filter , buffer , or zoom ), then processor can accurately convert them , at least for signal amplification to the system should be able to use level . Therefore, the selection of suitable design of the circuit components will play a multiplier role . Microchip Technology has introduced a programmable gain amplifier (Programmable Gain Amplifier, PGA) has amplifier , MUX , and gain selection using SPI bus controller integrated together , which can help users to effectively improve the system performance of the digital simulation of control . The new devices are designed for various industrial and instrumentation markets as well as signal and sensor processing use . New MCP6S2x amplifier devices in addition to providing functional , it can also provide digital control for the system design performance , the user can SPI bus in the system programming , and through the effective control plus and select input channels for greater design flexibility Sex . In addition, PGA does not require feedback and input resistance , therefore , can significantly reduce costs and save board space . Microchip Technology Inc. MCP6S21/2/6/8 an analog programmable gain amplifier (PGA) chip . The chip gain can be set to +1 ~ +32 V / V, and with input channel selection function, select the gain level through the SPI bus and the input channel to expand the micro- controller simulation input range , while reducing the input / output pins Amount of demand , thus reducing the cost of the microcontroller . In addition , a single signal path of the multi- channel system can also assist in the calibration of the simulation signal path to improve the accuracy of time and temperature . The device is especially suitable for wide band operation with low current amplifier , power supply and reduce demand for products . 1.1 chip pin definition New MCP6S21 and MCP6S22 with 8 -pin PDIP, SOIC and MSOP packages , MCP6S26 a 14 -pin PDIP, SOIC and TSSOP packages , MCP6S28 the 16- pin PDIP, SOIC and TSSOP packages . They pin arrangement shown in Figure 1 , Table 1 lists their pin functions . 2 Work MCP6S28 chip 's internal structure chart ( similar ) shown in Figure 2 . The figure shows , MCP6S2X chip by a simple function modules can be shared to complete multiple choice, variable gain control functions. MCP6S2X with Multiplexer Input (MUX) module , a total of eight-way input, software can set the channel selection . Unused input pins should be left vacant in order to minimize input current . Of course, then VDD or VSS , the chip can work ? but the input current becomes large . Internal op amp , which consists of op amp , the gain converter, ladder resistance (RLAD = RF + RG) etc. , complete signal amplification and bandwidth options to improve the accuracy of the output voltage . SPI logic control part of the main provider of chip select signal, synchronous clock, serial input and output , power on reset , control instructions and data reading and writing to complete the channel selection and gain control functions. Power-on reset circuit POR (Power-On Reset) function is : When the power supply voltage falls below the limit POR voltage ? VDD <VPOR ˜ 1.7V ?, so that the internal POR circuit resets all internal registers , and make chips run Shutdown mode . When VDD is greater than VPOR time , POR has to chip back to normal. In addition, the use of MCP6S26, MCP6S28 also the connection of multiple chips , the connections in the form of serial interface mode . Multi-chip connection , the first chip to be connected to the SO pin after the SI pin of a chip , and so on , they can share SCK and CS pin . 3 Several multiple comparison of data acquisition circuit In traditional circuit design , each analog signal Xuyong an op amp for voltage control and impedance matching , and then sent to the processing circuit (see Figure 3). Thus, in dealing with the traditional 4-way analog signal design, at least four op amps , 8 resistors, and occupy 4 processor I / O pins ( chip containing sample and hold A / D conversion) . To overcome the shortcomings of traditional design , multiplexing methods can be used , which is the most common way. It should be noted that many signals do not require continuous measurement, it can be used non- simultaneous sampling of the program . Need high-performance operational amplifier design, if the non- simultaneous sampling solution, he can be an operational amplifier , and then in front of it then a multiplexer (MUX), Zai Ji Road through it to pick Monixinhao To a common amplifier . This multiplexer will be in accordance with the processing requirements , the analog signals received from various quarters up the op amp . The realization scheme shown in Figure 4 . Multiplexer can be reduced using the traditional system design problems. It can take up the processor I / O down to one, all need to enlarge the signal only need a high-performance operational amplifiers can be . Component of the program by reducing the number of current and therefore need the space occupied by the circuit board also reduced . But at the same time , the program also need to increase the cost and quantity of certain components . Some relatively new device looks more cost-effective , but not easy to control , so not suitable for modern embedded control systems. To control or select signal gain , these devices are receiving processor , the same need to use more I / O pins . Therefore, this system uses the device more , is not conducive to further enhance the integration, but also vulnerable to interference . For the above , the use of a programmable gain amplifier MCP6S2X , then the processing described above, multi- channel analog signal system problems will be solved. Processor 's SPI port can be used to the commands sent to the MCP6S28 programmable gain amplifier in order to choose the processor which receives signals , but also can change the gain of the amplifier . Thus, it is possible to change the gain of each channel signal , but also changes in the signal processing gain at the same time . If the system detects the signal is too weak , the processor can increase the signal gain . When the signals reach a higher power in peacetime , the processor can reduce the gain . Figure 5 is a series of devices used MCP6S2x schematic design of the program . 4 Application Circuit Figure 6 MCP6S2X Series Chip hardware connection diagram ? the author in the design of " technological object simulation device " data acquisition boards ? project calls for heating the object to simulate ? the object as multiple-input multiple-output objects , which not only need to enter the temperature, Pressure and other parameters , but also a disturbance signal ( random noise and deterministic interference) . Multiple input parameters of the object is collected MCU , the MCU will be based on the transfer function of the object processing or data transmitted through the serial port for processing the computer simulation results ? and the final output . This design uses a 6 -channel MCP6S26 to do it because there is no three-wire system AT89C52 MCU serial bus interface , so it MCP6S26 in through the three -wire serial bus connection, the software should be used to simulate three-wire serial bus to operate , including the string Line clock, data input and data output . Thus, P1.7 can be used to simulate the chip select terminal CS, P1.4 analog clock input SCK, P1.6 analog data input SI, P1.5 analog data output SO. To save MCU I / O ports, the design also selected serial bus (I2C bus ) A / D conversion chip TLC0832. Click to enlarge To operate the controls on the MCP6S26 bytes and Shu Ju bytes Juncong SI Yinjiao??, and write the serial clock (SCK) Shangsheng Yan was Suocun . The data from the chip to read from the SO pin serial out , and the falling edge of the serial clock output . During the data exchange , CS must remain low . 5 Conclusion MCP6S2X programmable gain amplifier suitable for multi- channel signal acquisition circuit , which can be widely used in A / D converter driving control , data acquisition, test equipment , analog multiplexing applications , industrial and medical equipment and so on . Since the processor through software control of the analog signal circuit , so its high adaptability and flexibility . Programmable gain amplifier with MCP6S2X , the original design now require more components can be only one component , it can greatly simplify the previously complex circuit design and improve work efficiency.