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university:courses:alm1k:circuits1:alm-measure-outside-0-5-range [03 Nov 2018 16:26] – created Doug Merceruniversity:courses:alm1k:circuits1:alm-measure-outside-0-5-range [09 Jun 2020 16:22] – [Background:] Doug Mercer
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 <WRAP centeralign>Figure 1, External voltage divider options.</WRAP> <WRAP centeralign>Figure 1, External voltage divider options.</WRAP>
  
-It would be nice to not have to use a compensation capacitor, adjustable or otherwise. The ALICE Desktop software can adjust for any DC gain and offset when using an external divider. A digital (software) frequency compensation feature is also included in ALICE 1.2 (down load the latest version from [[https://github.com/analogdevicesinc/alice/releases|GitHub]]).+It would be nice to not have to use a compensation capacitor, adjustable or otherwise. The ALICE Desktop software can adjust for any DC gain and offset when using an external divider. A digital (software) frequency compensation feature is also included in ALICE 1.3 (down load the latest version from [[https://github.com/analogdevicesinc/alice/releases|GitHub]]).
    
 The software frequency compensation for each channel consists of a cascade of two adjustable [[https://en.wikipedia.org/wiki/High-pass_filter#Algorithmic_implementation| first order high pass filters]]. The time constant and the gain of each stage can be adjusted. Normal first order high pass filters do not pass DC so a DC gain of 1 path is added to the overall second order high pass software compensation filter. This structure is often called a shelving filter because of the shape of its frequency response. The software frequency compensation for each channel consists of a cascade of two adjustable [[https://en.wikipedia.org/wiki/High-pass_filter#Algorithmic_implementation| first order high pass filters]]. The time constant and the gain of each stage can be adjusted. Normal first order high pass filters do not pass DC so a DC gain of 1 path is added to the overall second order high pass software compensation filter. This structure is often called a shelving filter because of the shape of its frequency response.
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 <WRAP centeralign>Figure 3, Settings for just 1.0 MΩ R<sub>1</sub></WRAP> <WRAP centeralign>Figure 3, Settings for just 1.0 MΩ R<sub>1</sub></WRAP>
  
-As we can see in figure 3, the DC gain setting is slightly more than 2 which is to be expected based on the internal 1 MΩ resistor and external 1 MΩ R<sub>1</sub> resistor forming a 2:1 voltage divider. There is a small DC offset due to the leakage current from the ESD protection diodes on the M1k inputs and the parallel combination of R<sub>INT</sub> and R<sub>1</sub>.+As we can see in figure 3, the DC gain setting is slightly more than 2 which is to be expected based on the internal 1 MΩ resistor and external 1 MΩ R<sub>1</sub> resistor forming a 2:1 voltage divider. There is a small DC offset due to the leakage current from the ESD protection diodes on the M1K inputs and the parallel combination of R<sub>INT</sub> and R<sub>1</sub>.
    
 The input gain factor of 2 (2.17 to be exact) increases the allowable measurement range from 0 to +5 V to about 0 to +10 V. Enough to work with circuits powered from a 9 V battery for example. The input gain factor of 2 (2.17 to be exact) increases the allowable measurement range from 0 to +5 V to about 0 to +10 V. Enough to work with circuits powered from a 9 V battery for example.
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 <WRAP centeralign>Figure 8, R<sub>1</sub> = 1.0 MΩ, R<sub>2</sub> = 200 KΩ, R<sub>3</sub> = 470 KΩ with (orange), without (dark orange) compensation</WRAP> <WRAP centeralign>Figure 8, R<sub>1</sub> = 1.0 MΩ, R<sub>2</sub> = 200 KΩ, R<sub>3</sub> = 470 KΩ with (orange), without (dark orange) compensation</WRAP>
  
-Finally, a common 10X (passive) scope probe can be used. To connect the probe to the Channel B input of the M1k just a BNC connector with short leads terminated in male pins is used. The input end of the probe is connected to the Channel A output to test/calibrate the divider as shown in the photo of figure 9. It is difficult to inject a DC offset when using the probe so the input voltage range will be just positive voltages up to 10X the 0-5 V native range of the M1k or 0 to +50 V.+Finally, a common 10X (passive) scope probe can be used. To connect the probe to the Channel B input of the M1K just a BNC connector with short leads terminated in male pins is used. The input end of the probe is connected to the Channel A output to test/calibrate the divider as shown in the photo of figure 9. It is difficult to inject a DC offset when using the probe so the input voltage range will be just positive voltages up to 10X the 0-5 V native range of the M1k or 0 to +50 V.
  
 {{ :university:courses:alm1k:circuits1:input-comp-figure-9.png?500 |}} {{ :university:courses:alm1k:circuits1:input-comp-figure-9.png?500 |}}
  
-<WRAP centeralign>Figure 9, scope probe connected to M1k</WRAP>+<WRAP centeralign>Figure 9, scope probe connected to M1K</WRAP>
  
 {{ :university:courses:alm1k:circuits1:input-comp-figure-10.png?500 |}} {{ :university:courses:alm1k:circuits1:input-comp-figure-10.png?500 |}}
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 <WRAP centeralign>Figure 11, 10X scope probe with (orange), without (dark orange) compensation</WRAP> <WRAP centeralign>Figure 11, 10X scope probe with (orange), without (dark orange) compensation</WRAP>
  
-With the software frequency compensation feature in ALICE 1.2 and a couple of resistors you can measure just about any range of voltages you need. Obvious first choices would be to use a 1 MΩ for R<sub>1</sub> and either 1 MΩ, 470 KΩ, 200 KΩ or 100 KΩ for R<sub>2</sub>with R<sub>3</sub> left open. It is good practice to keep one or more of these simple voltage dividers installed at one end of your breadboard (to keep it away from any high frequency switching noise from DC-DC power converters or regulators) for use at all times.+With the software frequency compensation feature in ALICE 1.3 and a couple of resistors you can measure just about any range of voltages you need. Obvious first choices would be to use a 1 MΩ for R<sub>1</sub> and either 1 MΩ, 470 KΩ, 200 KΩ or 100 KΩ for R<sub>2</sub>with R<sub>3</sub> left open. It is good practice to keep one or more of these simple voltage dividers installed at one end of your breadboard (to keep it away from any high frequency switching noise from DC-DC power converters or regulators) for use at all times.
  
 **For Further Reading:** **For Further Reading:**
university/courses/alm1k/circuits1/alm-measure-outside-0-5-range.txt · Last modified: 17 Jan 2023 15:40 by Doug Mercer

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