chapter7 AD DA.pptVIP

3.properties §2 A/D converter (ADC) 1.Sample circuit ⑶sample keep circuit ⒉ quantity code Ⅳ、main techonlogy guidline Example1： * Chapter Ⅶ AD, DA §1 D/A Converter (DAC) Digital-Analog Converter Ⅰ.The basic principle and properties of D/A converter Convert the every bit of the inputing binary code into the analog quantity,according to their weight; then get their sum，the total analog sum is direct ratio to the digital quantity，so we realize the DAC. Conversion property:the ralation of the input and output. The above picture is the D/A conversion property of the inputing 3 bits binary. The ideal D/A property is that the output is direct ratio to the input. uo=Ku×D ;Ku voltage scale-up factor. the output analot currentio=Ki×D。;Ki current scale-up factor ， D:the decimal represented by binary. if the input is n binary bits dn-1dn-2…d1d0，the output analog voltage is： The given digital D/A conversion： ⑴Expansion according to weight，ask their analog； ⑵Sum，and ask the sum； ⑴resistance net：expansion; ⑵switch: digital quantity； ⑶sum: add analog. The structure of DAC： multiforms。 Transistor or MOS。 Operational amplifier Ⅱ、binary weighted net DAC Electronic circiut：d＝1→connect“-”;d=0 →connect“+” whichever end does the d connect（ ground or real ground），The branch current is invariable Sum circuit ⒈circuit supposeRF=R/2 ⒉ conversion principle ⒊output Ⅲ.T mode resistance net DAC 1.Circuit Electronic switch：d＝1→connect“VR”;d=0 →connect“Ground” 2.Conversion principle ① VR the voltage from S0 to D S0connectVR S1 S2 S3connect GND Equivalent circuit： So，when d3d2d1d0＝0001 The same as，when d3d2d1d0＝0010 When d3d2d1d0＝0100 When d3d2d1d0＝1000 ② when d3d2d1d0is variable, the voltage of D： Take Rf＝3R ： output： ①the switch is between the resistance net and the VR。 ②the place which is connected to Si iis changes from GND → VR， it need to build the correspondence VD ，and affect its speed. ③the time of every switch is different ，it is possible to produce point impuls