# Patent

## Title
Single wire system clock signal generation

## Abstract

This specification describes an integrated circuit comprising: a single wire interface; a clock circuit configured to detect a voltage from the single wire interface and to generate a clock signal having a frequency that is based on the detected voltage; and a digital system coupled with the single wire interface and the clock circuit. The digital system is configured to: receive a data signal from the single wire interface; power the digital system using a power signal from the single wire interface; and perform one or more operations clocked by the clock signal.

## Background
TECHNICAL FIELD
This disclosure relates generally to electronics and more particularly to single wire systems.
BACKGROUND
In an example scenario, a system can use a single interface for both data communications and power. For example, some single wire systems have two pins, one for the single wire interface and one for ground. Some single wire systems are driven by a fixed value pull-up resistor. There, the system power is limited by design to be within the limits of the specified resistor value. The system design can be matched to this value.
Additionally, in one example scenario, various chips are configured to operate at lower voltages, and the current demands may exceed the amount of current that may be supplied with a simple resistor. To meet those demands, some systems may be designed to operate in two modes: input/output (I/O) mode and execution mode. During I/O mode, the resistor would power the system. During execution mode, the user would provide an alternate power source, typically an output from another chip, to provide extra drive.
However, in an example scenario, two-mode systems can have disadvantages compared to simpler systems. For example, a two-mode system may implement timing control from the user, where the user must know when to turn on the alternate source, and when to turn it off to allow I/O. As another example, the two-mode systems may be designed to handle the execution mode current through the alternate source. The alternate source may be designed to meet certain design tolerances to meet multiple maximum requirements of the chip, e.g., timing and power requirements.
SUMMARY
This specification describes an integrated circuit comprising: a single wire interface; a clock circuit configured to detect a voltage from the single wire interface and to generate a clock signal having a frequency that is based on the detected voltage; and a digital system coupled with the single wire interface and the clock circuit. The digital system is configured to: receive a data signal from the single wire interface; power the digital system using a power signal from the single wire interface; and perform one or more operations clocked by the clock signal.
The details of one or more disclosed implementations are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings and the claims.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of an example system including a single wire system and a user system.
FIG. 2 is a block diagram of an example clock circuit.
FIG. 3 is a chart of an example frequency response curve for the clock circuit of FIG. 1.
FIG. 4 is a flow diagram of an example process performed by the clock circuit of FIG. 1.



DETAILED DESCRIPTION
System Overview
FIG. 1 is a block diagram of an example system 100 including a single wire system 102 and a user system 104. The single wire system 102 can be an integrated circuit and the user system 104 can be any appropriate device that is configured to provide both power and input/output for the single wire system 102.
The single wire system 102 includes a single wire interface 106. The single wire interface 106 can be a pin on an external portion of an integrated circuit. The user system 104 can be coupled with the single wire system 102 by wire bonding to the single wire 106 or by any other appropriate electrical coupling.
The single wire system 102 includes a digital system 108 and a clock circuit 110. The clock circuit 110 provides a clock signal to the digital system 108. The digital system 108 can be implemented as any appropriate digital circuit. The digital system 108 is configured to provide a specified logic function for the single wire interface 106.
The digital system 108 can perform any of one or more appropriate logic functions. For example, the digital system 108 can perform an identification function or a cryptographic function. The user system 104 can provide data to the digital system 108 using the single wire interface 106, and the digital system 108 can then process the data. The digital system 108 returns the processed data to the user system 104 using the single wire interface 106. The digital system 108 load current is primarily controlled by the frequency of the clock signal, and the performance of the digital system 108, e.g., the time to perform a specified operation, is tied to the frequency of the clock signal.
While the digital system 108 is performing a logic function, the single wire system 102 draws power from the single wire interface 106. The clock circuit 110 is configured to dynamically adapt the frequency of the clock signal based on the available power of the system 102 by detecting a voltage from the single wire interface 106 and generating a clock signal having a frequency based on the detected voltage. For example, the clock circuit 110 can adjust the frequency of the clock signal to be proportional to the detected voltage.
Because the voltage at the single wire interface 106 will switch between a high and a low voltage as input and output are generated, that voltage may not be suitable for controlling the clock circuit 110 to generate the clock signal. The single wire system 102 can rectify the input signal at the single wire interface 106 and supply the rectified signal to the clock circuit 110. For example, a diode and a capacitor can be used to rectify the input signal.
In some implementations, the clock circuit 110 is configured to detect a rectified voltage from the single wire interface 106 over a period of time and adjust the frequency of the clock signal based on the detected rectified voltage. In some implementations, the clock circuit 110 is configured to adjust the frequency of the clock signal to a target frequency within a range of specified frequencies based on a difference between the detected voltage and a threshold voltage.
In some implementations, the clock circuit 110 is configured to decrease the frequency of the clock signal in response to determining that the detected voltage is below a threshold voltage. This can be useful, for example, so that the digital system 108 can continue operating as the voltage drops, albeit at a slower pace. The user system 104 can freely trade between chip performance and power available without having to redesign the user system 104 or reconfigure the single wire system 102.
The clock circuit 110 can be implemented as a digital circuit, e.g., using digital divider circuits, or as an analog circuit, e.g., using any appropriate voltage-frequency technology, or as a combination of both. A voltage controller oscillator can be used to implement the clock circuit 110. In some implementations, the clock circuit 110 is configured to stop generating the clock signal if the detected voltage from the single wire interface drops to zero for a period of time, indicating an input signal from the user system 104.
In some implementations, the single wire system 102 is an integrated circuit having only two pins, one for ground and one for the single wire interface 106. In some other implementations, the single wire system 102 has other pins in addition to the single wire interface 106.
Example System
FIG. 2 is a block diagram of an example system 200 including an example single wire system 202 and an example user system 204. The user system 204 is coupled with the single wire system 202 by a single wire interface 206, e.g., a pin on an integrated circuit.
The single wire system 202 includes a digital system 208 and a clock circuit 210. The clock circuit is configured to detect a voltage from the single wire interface 206 by a connection through a diode 212. The single wire system 202 includes a capacitor 214 that provides charge storage for the digital system 208 when the voltage at the single wire interface 206 is at a low voltage, e.g., ground. The clock circuit 210 generates a clock signal based on the detected voltage from the single wire interface 206 and provides the clock signal to a CLK interface on the digital system 208.
The clock circuit 210 is configured to dynamically adapt the frequency of the clock signal based on the available power of the single wire system 202 by detecting a voltage from the single wire interface 206 and generating a clock signal having a frequency based on the detected voltage. The clock circuit 210 typically detects the voltage at a node behind the single wire interface 206 itself because the voltage there alternates between high and low. For example, the clock circuit 210 can use a voltage detected at a node between the diode 212 and the capacitor 214 that provides a rectified input voltage. In other examples, the clock signal can detect the voltage at any appropriate point within the single wire system that is representative of the available power to the system.
The digital system 208 receives data at an IN interface by a connection to the single wire interface 206. The digital system 208 outputs data at an OUT interface by a connection to the single wire interface 206 through a transistor 216.
The user system 204 provides power to the single wire system 202 using a pull-up resistor 220. The user system 204 can also provide alternative power from an ALT interface using a transistor 222 coupled with the pull-up resistor 220. The user system 204 receives data at an IN interface by a connection to the single wire interface 206 through a buffer 224. The user system 204 outputs data at an OUT interface by a connection to the single wire interface 206 through a transistor 226.
Example Frequency Response Curve
FIG. 3 is a chart 300 of an example frequency response curve 302 for the clock circuit 110 of FIG. 1. The horizontal axis plots the detected voltage from the single wire interface 106, and the vertical axis plots the frequency of the clock signal as generated by the clock circuit 110.
Between detected voltages of VMAX and VMIN, the clock circuit 110 adjusts the frequency of the clock signal to be proportional to the detected voltage. The clock circuit 110 adjust the frequency of the clock signal to a target frequency between upper and lower limits of fMIN and fMAX. If the detected voltage drops below VMIN, the system can respond in one of several ways. In a first example, the generated frequency will remain at fMIN until the system can no longer function. In a second, example, the internal clock is stopped. Stopping the clock can be useful for example, so that the user system 104 can drop a supplied voltage to cause the detected voltage to drop below VMIN as an indication to halt the operation of the system 102.
Although the curve as illustrated 302 has a constant slope, the clock circuit 110 can be configured to respond in other ways. For example, where the clock circuit 110 is implemented as a digital circuit, an arbitrary curve can be programmed into the clock circuit 110. The curve can be a parabolic curve, dropping slowly when the detected voltage is near VMAX and dropping rapidly as the detected voltage approaches VMIN.
Example Flowchart
FIG. 4 is a flow diagram of an example process 400 performed by the clock circuit 110 of FIG. 1.
The clock circuit 110 detects a voltage from the single wire interface 106 (402). For example, the clock circuit 110 can detect a rectified voltage from the single wire interface 602. The clock circuit 110 can detect a rectified voltage from the single wire interface 602 over a period of time. The period of time can be selected based on an anticipated data speed for the single wire interface. The voltage varies as the user system 104 provides data or provides a signal that lacks data but provides power.
The clock circuit 110 generates a clock signal having a frequency based on the detected voltage (404). For example, the frequency can be proportional to the detected voltage. The clock circuit 110 can decrease the frequency as the detected voltage drops, which results in the digital system 108 operating at a reduced speed.
The clock circuit 110 determines whether the detected voltage drops below a threshold voltage (406). The voltage dropping below the threshold voltage can be an indication from the user system 104 to cease operations. If the detected voltage drops below the threshold voltage, the clock circuit 110 ceases generating the clock signal. If the detected voltage does not drop below the threshold voltage, the clock circuit 110 continues detecting the voltage and generating the clock signal (return to 402).
Particular embodiments of the subject matter described in this specification can be implemented so as to realize one or more of the following advantages. First, a single wire system can be clocked at a frequency based on available power. Second, a user system of the single wire system can be more flexible, e.g., by trading between system performance and power available without redesigning the user system or reconfiguring the single wire system. Third, the single wire system can continue to operate by reducing the clock frequency when the available power drops.
While this document contains many specific implementation details, these should not be construed as limitations on the scope what may be claimed, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable sub combination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can, in some cases, be excised from the combination, and the claimed combination may be directed to a sub combination or variation of a sub combination

## Claims

1. An integrated circuit comprising:
a single wire interface;
a clock circuit configured to detect a voltage from the single wire interface and to generate a clock signal based on the detected voltage, a frequency of the clock signal being adapted based on the detected voltage, the single wire interface being external to the clock circuit; and
a digital system coupled with the single wire interface and the clock circuit, the digital system configured to:
receive a data signal from the single wire interface;
power the digital system using a power signal received from the single wire interface; and
perform one or more operations clocked by the clock signal.

2. The integrated circuit of claim 1, wherein the clock circuit is configured to decrease the frequency of the clock signal in response to determining that the detected voltage is below a threshold voltage, thereby decreasing an operational speed of the digital system.

3. The integrated circuit of claim 1, wherein the clock circuit is configured to adjust the frequency of the clock signal to a target frequency within a range of specified frequencies based on a difference between the detected voltage and a threshold voltage.

4. The integrated circuit of claim 1, wherein the clock circuit is configured to detect a rectified voltage from the single wire interface over a period of time and adjust the frequency of the clock signal based on the detected rectified voltage.

5. The integrated circuit of claim 1, wherein the clock circuit comprises a digital circuit comprising a plurality of frequency dividers.

6. The integrated circuit of claim 1, wherein the clock circuit comprises an analog circuit.

7. The integrated circuit of claim 1, wherein the clock circuit is configured to cease generating the clock signal if the voltage from the single wire interface drops to zero for a period of time.

8. The integrated circuit of claim 1, wherein the digital system is configured to perform one or more cryptographic operations.

9. The integrated circuit of claim 1, wherein the frequency is proportional to the detected voltage.

10. The integrated circuit of claim 1, wherein the frequency is between first and second other frequencies.

11. A method comprising:
receiving a data signal from a single wire interface of a digital system;
powering the digital system using a power signal received from the single wire interface;
detecting a voltage from the single wire interface;
generating, by a clock circuit, a clock signal based on the detected voltage, a frequency of the clock signal being adapted based on the detected voltage, the single wire interface being external to the clock circuit; and
performing, at the digital system, one or more operations clocked by the clock signal having the frequency based on the detected voltage.

12. The method of claim 11, comprising decreasing the frequency of the clock signal in response to determining that the detected voltage is below a threshold voltage, thereby decreasing an operational speed of the digital system.

13. The method of claim 11, comprising adjusting the frequency of the clock signal to a target frequency within a range of specified frequencies based on a difference between the detected voltage and a threshold voltage.

14. The method of claim 11, comprising detecting a rectified voltage from the single wire interface over a period of time and adjusting the frequency of the clock signal based on the detected rectified voltage.

15. The method of claim 11, comprising generating the clock signal using a digital circuit comprising a plurality of frequency dividers.

16. The method of claim 11, comprising generating the clock signal using an analog circuit.

17. The method of claim 11, comprising ceasing generating the clock signal if the voltage from the single wire interface drops to zero for a period of time.

18. The method of claim 11, comprising performing one or more cryptographic operations using the generated clock signal.

19. The method of claim 11, wherein the frequency is proportional to the detected voltage.

20. The method of claim 11, wherein the frequency is between first and second other frequencies.

21. A system comprising:
a user system; and
a single wire system coupled with the user system by a single wire interface, the single wire system comprising:
a single wire interface;
a clock circuit configured to detect a voltage from the single wire interface and to generate a clock signal based on the detected voltage, a frequency of the clock signal being adapted based on the detected voltage, the single wire interface being external to the clock circuit; and
a digital system coupled with the single wire interface and the clock circuit, the digital system configured to receive a data signal from the user system from the single wire interface, to power the digital system using a power signal from the user system from the single wire interface, and to perform one or more operations clocked by the clock signal.

22. The system of claim 21, wherein the clock circuit is configured to decrease the frequency of the clock signal in response to determining that the detected voltage is below a threshold voltage, thereby decreasing an operational speed of the digital system.

23. The system of claim 21, wherein the clock circuit is configured to adjust the frequency of the clock signal to a target frequency within a range of specified frequencies based on a difference between the detected voltage and a threshold voltage.

24. The system of claim 21, wherein the clock circuit is configured to detect a rectified voltage from the single wire interface over a period of time and adjust the frequency of the clock signal based on the detected rectified voltage.

25. The system of claim 21, wherein the frequency is proportional to the detected voltage.

26. The system of claim 21, wherein the frequency is between first and second other frequencies.