The present invention is generally related to circuits that monitor a signal to determine the percentage of time that the signal is active. More particularly, the present invention is related to an apparatus and method for sensing a digital signal and providing a multi-bit digital output code that indicates the percentage of time that the digital signal is active over a sampling time interval or sampling window.
Conventional central processor units (CPUs) such as microprocessors and microcontrollers are operated at internal frequencies that typically range anywhere from megahertz (MHz) to gigahertz (GHz) frequencies. As the internal frequencies are increased, the amount of heat that is generated within the CPU also increases. The internal heat levels associated with the CPU can potentially damage the electronics within the CPU. Signal monitoring is useful to monitor the thermal temperature associated with the CPU so that damage to the internal electronics of the CPU can be prevented.
Some conventional CPUs have an internal sensor that monitors the temperature of the CPU during operation. External signals, such as a processor hot signal (PROCHOT), are provided by the CPU to indicate when the internal temperature of the CPU has exceeded some predetermined threshold level. The CPU may also include internal circuitry to adjust the internal clock frequency (a process called throttling back or throttling). By lowering the clock frequency inside the CPU, the overall heat levels should begin to decrease over time. However, CPUs typically require an external device to dissipate the thermal energy and protect the CPU from damage.
CPU based systems typically dissipate heat through heat sinks. The heat sinks may be cooled by one or more fans. Noise levels associated with each fan can be high when each fan is rotating at a maximum speed level. It is often desirable to limit the rotational speeds associated with the fans to minimum acceptable levels for cooling so that noise levels are minimized.
A fan speed control unit can be used to adjust the speeds associated with the cooling fans. Each fan speed may be adjusted separately for optimal heat dissipation characteristics. The heat sink for the CPU can have a separate fan that has a speed that is adjusted based on the monitored temperature of the CPU. For example, the CPU fan speed can be increased when the internal temperature of the CPU increases, while the CPU fan speed can be decreased when the internal temperature of the CPU decreases.