155-0076-00: Difference between revisions
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==Probe Readout Ring Decoder== | ==Probe Readout Ring Decoder== | ||
The M94 has a circuit for decoding the probe attenuation factor based on the probe readout pin. | The M94 has a circuit for decoding the probe attenuation factor based on the probe readout pin. | ||
The probe readout pin contacts the readout ring on the probe input of the scope. | The probe readout pin contacts the readout ring on the probe input of the scope. | ||
The readout ring is pulled up to 5 volts by a 5 kΩ resistor outside of the M94. | The readout ring is pulled up to 5 volts by a 5 kΩ resistor outside of the M94. | ||
Inside the probe, there is a resistor between the readout pin and the ground of the BNC connector. | Inside the probe, there is a resistor between the readout pin and the ground of the BNC connector. | ||
This scheme allows the scope to distinguish 1x, 10x, and 100x probes, and adjust on-screen readout scale accordingly, | This scheme allows the scope to distinguish 1x, 10x, and 100x probes, and adjust on-screen readout scale accordingly, | ||
so that the on-screen scale is referenced to the voltage at the probe tip. | so that the on-screen scale is referenced to the voltage at the probe tip. | ||
Letting the ring float represents a 1x probe. | |||
11 kΩ to ground represents a 10x probe. | 11 kΩ to ground represents a 10x probe. | ||
6.2 kΩ to ground represents a 100k probe. | 6.2 kΩ to ground represents a 100k probe. | ||
Revision as of 10:14, 24 December 2018
The Tektronix 155-0076-00 (M94) is a Tek-made input protection and probe logic integrated circuit in a 16-pin minipac package, designed by John Addis.
Probe Readout Ring Decoder
The M94 has a circuit for decoding the probe attenuation factor based on the probe readout pin. The probe readout pin contacts the readout ring on the probe input of the scope. The readout ring is pulled up to 5 volts by a 5 kΩ resistor outside of the M94. Inside the probe, there is a resistor between the readout pin and the ground of the BNC connector. This scheme allows the scope to distinguish 1x, 10x, and 100x probes, and adjust on-screen readout scale accordingly, so that the on-screen scale is referenced to the voltage at the probe tip. Letting the ring float represents a 1x probe. 11 kΩ to ground represents a 10x probe. 6.2 kΩ to ground represents a 100k probe.