Patent Application
20060047991
The present invention relates to clock generation generally and, more particularly, to a real time clock architecture and/or method for a system on a chip (SOC) application.
Conventional system on a chip (SOC) designs need a real time clock. For example, a DVD recorder (or other recorder) needs to know when to wake up from a sleep mode to record a particular event, such as a TV program. The clock needs to keep the time even when the recorder is unplugged from the power supply. In particular, a quality recorder should not be blinking at “12:00” when the power supply is restored.
Conventional solutions use an external discrete real time clock (RTC) chip to hold time. Such chips normally use bipolar technology so that they are able to run on a button battery or other low voltage inexpensive battery. External discrete real time clock chips increase the overall cost of a design.
Other solutions integrate the clock onto the SOC chip. However, a SOC is not ideal for extremely low power applications (i.e., being powered by a button battery). A typical integrated clock needs to run on a re-chargeable battery only. Rechargeable batteries are expensive. Another approach is to integrate a clock into the SOC chip with special process. Such special processes are expensive and not practical on sub-micron technology.
It would be desirable to implement an inexpensive real time clock that minimized power usage.
The present invention concerns an apparatus comprising a first portion, a second portion and a processor. The first portion is configured to generate a count signal in response to a number of oscillations of a clock signal. The first portion is powered by an unswitched power source. The second portion is configured to generate an interrupt signal in response to the count signal and a predetermined stored value. The second portion is powered by a switched power source. The processor is configured to (i) receive the interrupt signal and (ii) generate the switched power.
The objects, features and advantages of the present invention include providing clock generation system that may (i) be implemented in a system on a chip (SOC), (ii) consume a limited amount of power, (iii) be implemented without special VLSI processes (e.g., using normal sub-micron process), (iv) work with a large variety of battery voltages (e.g., 1.2 volts to 3.3 volts), (v) work with standard lithium watch battery, rechargeable battery, super capacitor etc., (vi) provide an automatic low battery detection, (vii) provide flexibility by implementing features in software, (viii) be implemented with low cost without an external real time clock (RTC) chip, (ix) be fabricated with standard VLSI process, and/or (x) provide long battery life (e.g., >10 years) on standard watch battery.
These and other objects, features and advantages of the present invention will be apparent from the following detailed description and the appended claims and drawings in which:
Referring to
The counter 112 may be implemented as an asynchronous counter to avoid the need to implement clocking circuitry. An asynchronous counter normally uses less power than a synchronous counter. In one example, the counter 112 may be implemented as a 46-bit counter. However, other counters may be implemented to meet the design criteria of a particular implementation. A 46-bit counter may be useful if the crystal 116 is a 32,768 Hz crystal (e.g., the frequency of a standard watch crystal). 32,768/2ˆ15=1 second. 1 second*2ˆ31=2,147,483,648 seconds which equals 68 years. So a 46-bit counter driven by a 32,768 Hz crystal will count for 68 years, long beyond the useful life of a typical DVD recorder. A 45-bit counter will count for 34 years.
The internal portion 104 may be implemented as core logic (e.g., software run on a microprocessor, such as an embedded microprocessor or microcontroller). The internal portion 104 generally comprises a block (or circuit) 130, a block (or circuit) 132 and a block (or circuit) 134. The circuit 130 may be implemented as a voltage comparator circuit. The circuit 132 may be implemented as a comparator circuit. The circuit 134 may be implemented as a register. The register 134 may be configured to provide a timer interrupt signal (e.g., TIME). The signal TIME may be a multi-bit signal.
The external portion 102 may have an input 122 that receives a voltage (e.g., BAT) from an external source. The external source may be implemented as a battery, a capacitor, or other appropriate external power source. In one example, the external power may be a watch battery, re-chargeable battery, super capacitor or system power. The voltage comparator 130 may be powered by the external source through an input 123. The comparator 132 and the register 134 are generally powered by the same power supply that supplies the core logic in the processor 106. The counter 112 has an output 124 that presents a signal (e.g., COUNT). The signal COUNT may be a multi-bit signal. The comparator 132 has an input 136 that receives the signal COUNT and an input 138 that receives the signal TIME from the register 134. The comparator 132 compares the signal COUNT to the signal TIME to generate an interrupt signal (e.g., INT) presented through an output 140. The signal COUNT may be presented to an input 150. The signal INT may be presented to an input 152. An input 154 may receive the signal CLK. An input 156 may receive a signal (e.g.,. LOW) from the comparator 130.
The core logic 104 (which runs on the core power) comprises the voltage comparator 130, the comparator 132, the time register 134 and control logic/startup logic for the XTAL oscillator/counter (to be described in more detail in connection with
Referring to
The crystal 116 may be implemented, in one example, as a low cost external watch crystal. However, other types of low cost crystals may be implemented to meet the design criteria of a particular implementation. While the present invention may be suitable for use with a low cost crystal, the invention will work with any crystal that is convenient. The oscillator 110 may be implemented as a low power crystal (e.g., XTAL) oscillator. The oscillator 110 and the counter 112 run on external power. In general, the external portion 102 continues to operate even if the power source that runs the main core (e.g., the core power) of the chip is removed.
Referring to
The present invention may be implemented using standard sub-micron technology to minimize the transistors needed for implementation. The internal circuit 102 includes the oscillator 110 (with external clock xtal) and a single counter 112, so the transistors are kept to a minimum. Implementing the counter as a 31-bit second counter may be used to count up to more than 50 years.
Referring to
The rest of the clock generation system 100 (e.g., other than the external portion 102) is not implemented by hardware, but rather is normally implemented by the software of the internal portion 104. The embedded processor 106 reads the value in the counter 112, adds the retrieved difference value, and converts the value into seconds, minutes, date and year. The software 104 may also provide adjustments, such as for daylight savings time. Therefore, the real time clock has only a minimal part of logic run on the battery. The system 100 uses a partition between hardware/software to minimize the drain on the clock battery.
Referring to
The core logic 104 would compare the value in the counter 112 with some pre-set value. If the values match, the interrupt signal INT would be sent to the embedded processor 106 such that TV recording software (or other external software) could be started. The comparator 112 works on the main power, and thus would not drain the battery.
The system 100 may automatically detect a low battery condition by comparing the battery voltage with an internal band gap voltage generator. In many SOC chips, a band gap circuit is commonly implemented for other purpose. Thus, a battery low monitor is constructed with a simple voltage comparator and an existing band gap voltage generator.
The function performed by the software module 104 and a processor 106 of
The present invention may also be implemented by the preparation of ASICs, FPGAs, or by interconnecting an appropriate network of conventional component circuits, as is described herein, modifications of which will be readily apparent to those skilled in the art(s).
The present invention thus may also include a computer product which may be a storage medium including instructions which can be used to program a computer to perform a process in accordance with the present invention. The storage medium can include, but is not limited to, any type of disk including floppy disk, optical disk, CD-ROM, magneto-optical disks, ROMs, RAMs, EPROMs, EEPROMs, Flash memory, magnetic or optical cards, or any type of media suitable for storing electronic instructions.
While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention.
