This information is part of the Modelica Standard Library maintained by the Modelica Association.
This model is a negative resistor without thermal behavior which is described as a switched capacitor model (care for the schematic).
The clock source is inside the model, its frequency can be chosen by parameter. Also the resistance is a parameter, it has to be positive. The internal (switched) capacitor is parametrized in such a way that the total resistance is independently from the frequency equal to the negative value of the negative resistance parameter.
Cauer low-pass filter with operational amplifiers and switched capacitors