Differences
This shows you the differences between two versions of the page.
| Both sides previous revisionPrevious revision | |
| university:tools:m1k:alice:oscilloscope-x-y-user-guide [21 Nov 2022 16:25] – [Analog Inputs] Doug Mercer | university:tools:m1k:alice:oscilloscope-x-y-user-guide [17 Jan 2023 20:03] (current) – add cautionary note Doug Mercer |
|---|
| === Software Frequency Compensation=== | === Software Frequency Compensation=== |
| |
| The input capacitance, C<sub>INT</sub>, of the analog inputs in the high Z mode is approximately 390 pF (for the rev D design and slightly higher for the rev F design). This relatively large capacitance along with relatively high resistance dividers can significantly lower the frequency response. In figure In1 we again revisit the input structure of the M1k and connecting an external resistive voltage divider R<sub>1</sub> and R<sub>2,3</sub>. The contents of the blue box represent the input of the M1k in Hi-Z mode. To introduce an optional DC offset for measuring negative voltages resistor R<sub>2</sub> is included and could be connected to either the fixed 2.5V or 5V supplies on the M1k. The C<sub>INT</sub> and effective resistance of the divider network form a low pass pole in the frequency response. To give you a rough idea let's use 400 pF for C<sub>INT</sub> and 1 MΩ for the resistor divider. That would result in a low pass response with a 3 dB roll-off starting at around 400 Hz. | The input capacitance, C<sub>INT</sub>, of the analog inputs in the high Z mode is approximately 390 pF (for the rev D design and slightly higher for the rev F design). This relatively large capacitance along with relatively high resistance dividers can significantly lower the frequency response. In figure In1 we again revisit the input structure of the M1k and connecting an external resistive voltage divider R<sub>1</sub> and R<sub>2,3</sub>. The contents of the blue box represent the input of the M1k in Hi-Z mode. To introduce an optional DC offset for measuring negative voltages resistor R<sub>2</sub> is included and could be connected to either the fixed 2.5V or 5V supplies on the M1k. The C<sub>INT</sub> and effective resistance of the divider network form a low pass pole in the frequency response. |
| |
| A capacitor would generally be needed across the input resistor R<sub>1</sub> to frequency compensate the divider. Such a hardware solution generally requires the capacitor (or alternatively the divider resistors) to be adjustable. | <note>The ADALM1000 (Rev. F version) has the ability to separate the voltage measurement connection from the voltage / current output pin, the Split I/O mode control in the AWG settings. The size of the parasitic capacitance is significantly different when using the CH A/B pins in Hi-Z mode vs using the AIN/BIN pins. The required external compensation capacitor value will be very different between the two pins.</note> |
| | |
| | To give you a rough idea let's use 400 pF for C<sub>INT</sub> and 1 MΩ for the resistor divider. That would result in a low pass response with a 3 dB roll-off starting at around 400 Hz. A capacitor would generally be needed across the input resistor R<sub>1</sub> to frequency compensate the divider. Such a hardware solution generally requires the capacitor (or alternatively the divider resistors) to be adjustable. |
| |
| {{ :university:tools:m1k:alice:input-cir-figure-4a.png?500 |}} | {{ :university:tools:m1k:alice:input-cir-figure-4a.png?500 |}} |
