{"id":5423,"date":"2018-12-26T09:13:16","date_gmt":"2018-12-26T09:13:16","guid":{"rendered":"http:\/\/41j.com\/blog\/?p=5423"},"modified":"2019-01-02T13:16:38","modified_gmt":"2019-01-02T13:16:38","slug":"multislope-adc-bring-up-dual-slope","status":"publish","type":"post","link":"https:\/\/41j.com\/blog\/2018\/12\/multislope-adc-bring-up-dual-slope\/","title":{"rendered":"Multislope ADC Bring up (Dual slope)"},"content":{"rendered":"\n
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I’ve been playing with a multislope ADC design. Multislope ADC are often used in high end multimeters, and as I have a mild obsession with 8.5 digit multimeters<\/a>, I wanted to try making a multislope ADC. The current design, such as it is was developed with significant input from EEVBlog users (see this thread)<\/a>.\n\nThis post documents initial bring up and tests of the first revision of the PCB. Links to Kicad files, and data used in plots can be found at the end of this post.<\/p>\n\n\n\n

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Components used in this test<\/h2>\n\n\n\n

\nAll resistors are standard, cheap 1\/4 Watt metal film resistors. The large slopes are 47K. Small slopes 4.7M. The input resistor (R200) is also 47K.\n\nThe design uses a 2 opamp integrator. Notionally this allows you to combine an opamp with good low frequency response with one with good high frequency response. A voltage divider sits between the two opamps. R9 is 47Ohm, R8 1K.\n\nOn the output amplifier R3 is 1K and R7 is 470Ohm to give a gain of ~0.5. This allows the Arduino Mega which I’m using to control the amplifier to read almost the full positive range of the integrator output (12V).\n\nThe integrator capacitor is an NP0 10nF, Murata GRM3195C1E103JA01D.\n\nThe switches are all DG419s. This includes the part marked DG417 on the schematic, which resets the integrator. All the DG419s are Vishay DG419Bs MSOP8s, except for the integrator which uses an Analog ADG1419BRMZ (I ran out of Vishay DG419s). Update: I attempted to rebuild this circuit using only ADG1419BRMZ, it did not work well. My guess is that there is too much charge injection… charge injection is not listed in the datasheets…\n\nI’m using a LTZ1000 reference to supply the slopes. This sits on an 3458A A9 PCB. I’m using a A9 clone from here<\/a>.\n\nAll opamps are socketed. In this test I used a NE5534 on the output. An OPA177 and AD711 for the integrator, an AD711 on the input, and an LT1013 to buffer\/invert the reference voltage.<\/p>\n\n\n\n

Build Issues<\/h2>\n\n\n\n

There were a few errors in the schematic and layout. These include: <\/p>\n\n