+-----+        +-----------+          +-----+   +--------+   +-----+
|     |        |  Subject  |          |     |   |        |   |     |
| OSC o---+----o   under   o----------o     |   | low    |   |     |
|     |   |    |   test    |          | XOR o---o pass   o---o ADC |
+-----+   |    +-----------+    /-----o     |   | filter |   |     |
          |                     |     |     |   |        |   |     |
          ---------------------/     +-----+   +--------+   +-----+