This document addresses the challenges of digitizing signals in compact microcontroller designs where on-chip A/D converters may be insufficient or absent. It highlights issues such as signal noise, impedance, and reference levels that require conditioning before conversion.
The text evaluates operational amplifier options for single 5V supply systems, comparing CMOS and zero-drift technologies against bipolar alternatives. It provides specific circuit configurations using Linear Technology parts like the LT1013/LT1014 and LT1077 series combined with CMOS gates to achieve rail-to-rail output swing.
| Input Common Mode Range Limit (CMOS) | about 1V to 2.5V below the positive supply |
|---|---|
| CMOS Output Swing Accuracy | within a few millivolts of power supply rails |
| Minimum Supply Voltage for Full Range Operation | 6.5V |
| LT1026 Output Voltage (Low Current) | +9V |
| Noise Reduction Ratio with RC Filter | approximately 100:1 |
They cannot get close to the positive rail, with the input common mode range limit generally falling about 1V to 2.5V below it.
By using higher power supply voltages, such as utilizing the input to a local voltage regulator to run the analog circuitry.
Yes, the charge pump on a 5V RS-232 RX/TX chip can easily provide 10mA to an external load while still meeting the standard.