Abstract:
A multi-state switch network is provided that includes a serially connected diode pair configured to receive a single control signal at a control node. The serially-connected diode pair is configured to control a pair of switches. Moreover, the single control signal is operative to drive the serially connected diode pair to a first state, a second state, or a third state based at least in part on a state of the single control signal. Furthermore, the single control signal is operative to alternatively turn ON a first diode of the diode pair and turn OFF a second diode of the diode pair when the state of the single control signal is a first state, turn OFF the first diode and turn ON the second diode when the state of the single control signal is a second state, and turn OFF the first diode and turn OFF the second diode when the state of the single control signal is a third state.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 11/961,836, filed Dec. 20, 2007, which claims the benefit of Prov. Ser. No. 60/878,852, filed Jan. 5, 2007, and Prov. Ser. No. 60/937,853, filed Jun. 28, 2007, all of which are hereby incorporated by reference herein in their entireties for all purposes. 
    
    
     BACKGROUND OF THE INVENTION 
     This relates to multi-state switch network and more particularly to multi-state light-emitting diode (LED) network systems and methods. This also relates to systems and methods for maintaining the brightness of the LEDs within the multi-state LED network independent of battery voltage levels. 
     Typically, each switch within a switch network requires its own control signal. When these control signals are connected between multiple circuits and circuit boards, each control signal also requires its own I/O pin ON each circuit board. The same is true for LED circuits, which typically require individual control signals and pins to operate each LED. As the number of control signals and pins increases, the size of the circuit also increases. 
     Accordingly, what is needed are systems and methods for multi-state switch networks and multi-state LED networks that require fewer control inputs and that reduces the space required for control signals and pins. 
     The brightness of an LED varies based on the supplied voltage. Therefore, in battery-powered LED systems, the brightness of the LED is reduced as the voltage of the battery declines. 
     Accordingly, what is needed is a multi-state LED network that maintains the brightness of the LEDs substantially independently of the supplied voltage. 
     SUMMARY OF THE INVENTION 
     Systems and methods for multi-state switch networks and multi-state LED networks are provided. Systems and methods for maintaining the brightness of LEDs in multi-state LED networks are also provided. 
     A multi-state switch network can control the states of two switches using only one control signal. In a multi-state LED network, two LEDs can be controlled using only one control signal. These multi-state networks contain control circuitry that is connected to a pair of serially connected diodes. In a switch network embodiment, the diodes can be connected to switches. In a LED network embodiment, the diodes are LEDs. The control circuitry outputs a single control signal that is able to drive the pair of diodes in three different states. In a network of N diode pairs, N wires are sufficient to drive the 2*N diodes of the N diode pairs in 3 N  different states. 
     The control circuitry may also include a pulse-width modulator that controls the perceived brightness of the LEDs in a multi-state LED network. Pulse-width modulation can be used to vary the perceived brightness of an LED. A pulse-width modulated source connected to the LED can be used to turn the LED ON and OFF at a rate undetectable to the human eye. Increasing the amount of time the LED is turned OFF makes the LED appear dimmer while increasing the amount of time the LED is turned ON makes the LED appear brighter. Controlling the pulse-width modulation based at least in part on the battery voltage levels allows the control circuitry to maintain the brightness of the LEDs within the multi-state LED network substantially independently of supplied voltage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features of the present invention, its nature and various advantages will become more apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which: 
         FIG. 1  shows a schematic diagram of illustrative multi-state switch network  100  in accordance with an embodiment of the present invention. 
         FIG. 2  shows a schematic diagram of illustrative multi-state switch network  200  implemented in separate circuits in accordance with an embodiment of the present invention. 
         FIG. 3  shows a schematic diagram of illustrative multi-state switch network  300  having N diode pairs in accordance with an embodiment of the present invention. 
         FIG. 4  shows a timing diagram that illustrates the operation of multi-switch network  100  in accordance with an embodiment of the present invention. 
         FIG. 5  shows a schematic diagram of an illustrative multi-state LED network  500  with a pulse-width modulator in accordance with an embodiment of the present invention. 
         FIG. 6A  shows a continuous signal with a 100% duty cycle that may be used to drive multi-state LED network  500  in accordance with an embodiment of the present invention. 
         FIG. 6B  shows a continuous signal with a 66% duty cycle that may be used to drive multi-state LED network  500  in accordance with an embodiment of the present invention. 
         FIG. 6C  shows a continuous signal with a 50% duty cycle that may be used to drive multi-state LED network  500  in accordance with an embodiment of the present invention. 
         FIG. 7  is a simplified block diagram of a system that incorporates a multi-state switch network in accordance with an embodiment of the present invention. 
         FIG. 8  is a flowchart of an illustrative process in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Commonly assigned Terlizzi et al. U.S. patent application Ser. No. 11/824,203, filed Jun. 28, 2007, entitled “CONNECTORS DESIGNED FOR EASE OF USE” is hereby incorporated by reference in its entirety. 
       FIG. 1  shows a schematic diagram of illustrative multi-state switch network  100 . Multi-state switch network  100  includes diode pair  110  and control circuitry  120 . Control circuitry  120  controls the operation of diodes  104  and  106  within diode pair  110  using a single control signal  103 . 
     In one embodiment, diodes  104  and  106  are light-emitting diodes (LEDs). An LED can be directly driven to turn ON and turn OFF. In another embodiment, diodes  104  and  106  are connected to switches and the diodes may be driven to turn those switches ON and OFF. For example, nodes  112  and  114  may be connected to any suitable switches  116  including, for example, transistor switches, buffers, or any other logic circuits. For ease of explanation, in both embodiments the diodes will be referred to as being turned ON or OFF to indicate their states regardless of whether they are directly turned ON and OFF (e.g., an LED) or used to turn ON and OFF another device (e.g., a diode connected to a switch). 
     Diode pair  110  includes two diodes  104  and  106  connected in series between Vcc and ground. Diodes  104  and  106  can be of the same type or of different types. For example, diodes  104  and  106  can be different colored LEDs. Control signal  103 , connected to control node  108 , controls the state of diode pair  110 . When a high voltage level control signal is applied to control node  108 , diode  106  is turned ON and diode  104  is turned OFF. When a low voltage level control signal is applied to control node  108 , diode  104  is turned ON and diode  106  is turned OFF. When no voltage is applied to control node  108 , both diodes  104  and  106  can be turned OFF. When no voltage is applied to control node  108  by the control signal, control signal  103  is said to be in a high-impedance or HIGH-Z state. Thus, the two diodes of diode pair  110  may be operated in three different states using only a single control signal. These three states are illustrated in Table 1. The operation of diode pair  110  is illustrated in greater detail below with reference to the timing diagram of  FIG. 4 . 
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Three States of Diode Pair 110 
               
             
          
           
               
                   
                 Control 103 
                 Diode 104 
                 Diode 106 
               
               
                   
                   
               
               
                   
                 LOW-V 
                 ON 
                 OFF 
               
               
                   
                 HIGH-V 
                 OFF 
                 ON 
               
               
                   
                 HIGH-Z 
                 OFF 
                 OFF 
               
               
                   
                   
               
             
          
         
       
     
     Diode pair  110  also includes resistors  105  and  107 . The values of resistors  105  and  107  may be selected to provide appropriate bias voltage levels to diodes  104  and  106 . When properly biased, the voltage across each of the diodes may be approximately equal to the threshold voltages of the diodes when the diodes are supposed to be turned ON and the voltage across each of the diodes may be below the threshold voltage of the diodes when the diodes are supposed to be turned OFF. Different types of diodes have different threshold voltage levels, which may affect the selection of resistors  105  and  107 . Thus, the values of resistors  105  and  107  may be selected based on the voltage levels of the system and the properties of diodes  104  and  106 . 
     Control circuitry  120  can be used to generate control signal  103  that is used to control diode pair  110 . Control circuitry  120  can include tri-state buffer  121 . Tri-state buffer  121  receives input signal  122  and ON/OFF signal  123  and outputs control signal  103 . ON/OFF signal  123  can be used to switch diodes  104  and  106  of diode pair  1100 N and OFF. When ON/OFF signal  123  is ON, input signal  103  can be used to select which one of diodes  104  and  106  is turned ON. Additional circuitry that generates signals  122  and  123  can also be included within control circuitry  120  or can be received from another circuit. 
     Diode pair  110  and control circuitry  120  can be connected together within the same circuits as shown in  FIG. 1  or may be located in separate circuits as shown in  FIG. 2 .  FIG. 2  shows control circuitry  220  implemented in a first circuit  200   a  and LED pair  210  implemented in a second circuit  200   b . Circuits  200   a  and  200   b  are connected using any suitable wire or connector  230 . For example, connector  230  may be used to connect the first circuit  200   a  and the second circuit  200   b  implemented on flexible printed circuit boards. 
       FIG. 3  shows a network of N diode pairs  310  connected to control circuit  320 . Diode pairs  310  and control circuit  320  are the same or substantially similar to their counterparts in multi-state switch network  100 . In this arrangement, the 2*N diodes of the N diode pairs  310  can be controlled using only N control signals  303  that are output from control circuit  320 . Control circuit  320  can have a drive strength approximately N times the drive strength of control circuit  120  ( FIG. 1 ) in order to drive the N control signals  303 . As described above with respect to multi-state switch network  100 , each of the N diode pairs  310  can be driven to three different states using only one control wire. Thus, it can be seen that the 2*N diodes of the N diode pairs  310  can be driven to 3 N  different states using only N wires. Thus, the number of wires and connectors that are required to control a plurality of LEDs or switches may be reduced. 
       FIG. 4  shows a timing diagram  400  which illustrates the operation of multi-state switch network  100 . At time  400 , ON/OFF signal  123  is at a low voltage level. Thus, tri-state buffer  121  ( FIG. 1 ) is turned OFF, control signal  103  is in a high-impedance state, and both diodes  104  and  106  are turned OFF. At time  401 , ON/OFF signal  123  is switched to a high voltage level, turning ON tri-state buffer  121 . Input signal  122  is at a low voltage level and therefore control signal  103  is also at a low voltage level. In response to the transition of control signal  103  from a high-impedance state to a low voltage level, diode  104  is turned ON and diode  106  remains OFF. At time  402 , input signal  122  is driven to a high voltage level, which switches control signal  103  to a high voltage level. In response to this transition, diode  104  turns OFF and diode  106  turns ON. At time  403 , input signal  422  is brought to a low voltage level, therefore control signal  103  is also brought to a low voltage level. In response, diode  104  turns ON and diode  106  turns OFF. Finally, after time  404 , ON/OFF signal  122  is cycled between a high voltage level and a low voltage level, which causes output signal  103  to cycle between a low voltage level and a high-impedance state. As a result, Diode  104  is cycled ON and OFF. LED  106  remains turned OFF for this entire period. 
     When used in a battery-powered system, the perceived luminous intensity or brightness of an LED may decrease as battery voltage level decreases. However, if the brightness of an LED can be adjusted, the brightness of the LED can be increased as the battery voltage decreases in order to keep the brightness level of the LED substantially constant. 
       FIG. 5  shows a schematic diagram of an illustrative multi-state LED network  500  with a pulse-width modulator  550  that is adjustable to control the perceived brightness of the LEDs. Multi-state switch network  500  includes diode pair  510  and control circuitry  520 , which are the same or substantially similar to their counterparts in multi-state switch network  100 . Diode pair  510  contains two LEDs  504  and  506 . 
     Pulse-width modulator  550  can be used to control the perceived brightness of LEDs  504  and  506 . Whenever LEDs  504  or  506  are turned ON, pulse-width modulator  550  causes tri-state buffer to generate a control signal  503  that provides diode pair  510  with a series of discrete pulses instead of a continuous high or low voltage signal. As a result, LEDs  504  and  506  are rapidly pulsed ON and OFF rather then being ON continuously. When the pulse rate is sufficiently quick, the human eye is unable to detect the pulsing and will instead see the LED as continuously ON. 
     Duty cycle is a measure of the ratio of the duration of a particular phenomenon in a given period to the duration of the period. In this instance, the phenomenon is the duration that the LED is turned ON. Thus, when the LED is continuously turned ON it has a duty cycle of 1 or 100%. Varying the duty cycle of ON/OFF signal  523 , which varies the duty cycle of control signal  503 , controls the duty cycle of the LED and therefore the perceived brightness of the LED. Reducing the duty cycle of the LED reduces the perceived brightness of the LED, while increasing the duty cycle of the LED increases the perceived brightness of the LED. 
       FIG. 6A  shows a continuous high voltage signal, i.e., a high voltage signal with a 100% duty cycle.  FIG. 6B  shows the same high voltage signal of  FIG. 6A  with a 66% duty cycle and  6 C shows the same signal with a 50% duty cycle. The signal with the highest duty cycle (i.e.,  FIG. 6A ), when applied to control circuitry  520 , may cause LED  506  to appear brighter than when the signals with lower duty cycles are applied (i.e.,  FIGS. 6B and 6C ). The signal of  FIG. 6C  may cause the lowest perceived brightness of the three signals. 
     Pulse-width modulator  550  has a modulation control input  551  that can be used to vary the duty cycle of the output of pulse-width modulator  550  in order to control the perceived brightness of LEDs  504  and  506 . PWM control input  551  can receive a signal from a battery voltage level monitor (not shown) that is indicative of the charge of the battery. The battery voltage monitor can include, for example, an analog to digital converter (ADC), a comparator with adjustable thresholds, or multiple comparators with set thresholds, or any other suitable circuitry. When the battery fully charged, pulse-width modulator  550  may be set to provide the LEDs with a decreased perceived brightness level. Then as the battery voltage level decreases, PWM control input  551  can control pulse-width modulator  550  to increase the perceived brightness levels of the LEDs to compensate for the diminished voltage provided to the LEDs. 
     For example, a signal with a 50% duty cycle may cause the LEDs to provide sufficient perceived brightness when the battery at a fully charged voltage level, but as the battery weakens the duty cycle may be increased to 75% to increase the perceived brightness of the LEDs. Thus, by increasing the perceived brightness of the LEDs as the battery voltage level decreases, the perceived brightness of the LED may be maintained at a substantially constant level independent of the voltage level of the battery. 
       FIG. 7  shows a simplified block diagram of a system that incorporates a multi-state switch network. System  700  includes processor circuitry  710 , power distribution circuitry  720 , and switch network circuitry  730 . Processor circuitry  710  can include a processor and auxiliary circuitry that works with the processor. Processor circuitry  710  can coordinate all of the operations in system  700 , including, for example, controlling power distribution circuitry  720  and switch network  730 . In some embodiments, processor circuitry  710  may include control circuitry (e.g., control circuitry  120  of  FIG. 1 ) that may provide control signals to switch network  730 . Switch network  730  may include one or more diode or LED pairs, each controlled by a signal control signal. 
     Power distribution circuitry  720  can include over-voltage protection and fuse  721 , li-poly battery protection  722  and thermistor  723 . Over-voltage protection and fuse  721  can protect system  700  in the event that an unsafe amount of voltage is applied to one or more inputs. The fuse in the protection circuitry can be any over-current protection device which disconnects the circuit it is coupled with if an over-current condition is present. Li-Poly battery protection circuitry  722 , can include circuitry to prevent the malfunction of a li-poly battery which could result in a dangerous overheating situation. Li-poly battery protection circuitry  722  is typically built into battery packs as integrated protection circuitry. In accordance with the present invention, this circuitry can be separated from the battery and located anywhere within system  700 . Thermistor  723  can be located in the proximity of a battery (not shown) so that the resistance of the thermistor is indicative of the battery&#39;s temperature. One or more inputs of processor circuitry  710  can be electrically coupled with thermistor  733  so that the processor can monitor the temperature of the battery. Processor  710  can be programmed to charge the battery differently depending on the temperature of the battery. For example, processor  710  can vary the battery charging current according to the detected temperature. In order to extend the life of a battery, it is beneficial to charge the battery only when it is within a certain temperature range. By regulating the charging in this manner, one can extend the life of a battery beyond what would typically be expected. Power distribution circuitry  720  can also monitor the charge level of the battery and provide this information to switch network  730  in order to adjust the perceived brightness of any LEDs located within switch network  730 . This battery charge level information can be provided directly from power distribution circuitry  720  to switch network  730  or may be provided by way of processor circuitry  710 . 
     A detailed description of the design and function of exemplary systems that can incorporate circuits similar to switch network  730  can be found in the U.S. patent application entitled “CONNECTORS DESIGNED FOR EASE OF USE,” which is incorporated herein. 
       FIG. 8  shows a flowchart of process  800  for adjusting the perceived brightness of an LED within a multi-state LED network in accordance with the present invention. At step  810 , a diode pair receives a control signal that turns ON an LED in a diode pair. For example, in LED network  500  of  FIG. 5 , diode pair  510  may receive a high voltage level control signal  503  that turns ON LED  506 . At step  820 , the voltage level of a power source, such as a battery, can be monitored until there is a change in the voltage level at step  830 . If there is a change in the voltage level, at step  840  the duty cycle of the control signal can be adjusted. For example, with reference to LED network  500  of  FIG. 5 , if the voltage level decreases, PWM control signal  551  can be adjusted which may cause pulse-width modulator  550  to increase the duty cycle of control signal  503 . This increase in the duty cycle of control signal  503  may increase the perceived brightness of LED  506 , which may offset any decrease in the perceived brightness caused by any reduction in the voltage level. 
     Thus it is seen that the systems and method for multi-state switch networks are provided. Those skilled in the art will appreciate that the invention can be practiced by other than the described embodiments, which are presented for purposes of illustration rather than of limitation, and the invention is limited only by the claims which follow.