Abstract:
Embodiments of the present invention relate to systems and methods for an electronic hook switch for customer premises equipment. In an embodiment, a system includes a first lead configured to be coupled to a tip wire and a second lead and the second lead to a ring wire. A diode bridge is coupled to the first lead and the second lead had a positive output. A low side switch is coupled to the positive output of the diode bridge without a high side switch between the low side switch and the positive output of the diode bridge.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a continuation of U.S. application Ser. No. 10/400,648, filed Mar. 28, 2003, which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/438,532 filed Jan. 8, 2003, which are both incorporated herein by reference in their entireties. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     Embodiments of the present invention relate to customer premises equipment.  
         [0004]     More particularly, embodiments of the present invention relate to systems and methods for an electronic hook switch for customer premises equipment.  
         [0005]     2. Background Information  
         [0006]     While telephone infrastructure varies from country to country, the United States infrastructure provides a useful starting point for purposes of describing background information and embodiments of the present invention. Naturally, the embodiments described herein are useful in other contexts. In the United States, a landline phone can be a cordless or corded telephone that is coupled to a central office (“CO”) of a local exchange carrier (“LEC”) such as a Regional Bell Operating Company (“RBOC”), a competitive local exchange carrier (“CLEC”), and so on. Cordless telephones have no cord between the handset and base, each of which have a radio transmitter, receiver and antenna for communications between the handset and base. Typically, the handset includes a rechargeable battery, and the base is powered by current from an alternating current (“AC”) outlet (e.g., of a house, office, etc.). The range of effective communications between the handset and base can be from 10 feet to several miles depending on factors such as product design, operating radio frequency(s), environmental conditions, and legal restrictions (e.g., laws, regulations, etc.). Examples of known operating radio frequencies for cordless telephone communications in the United States include 900 Megahertz (“MHz”), 2.4 Gigahertz (“GHz”), 5.8 GHz, a combination thereof, and so on.  
         [0007]     In a residential environment, the base is typically coupled to the CO via one or more wires, such as an RJ-11 wire that couples the base to an RJ-11 jack on a wall or in a floor. The RJ-11 jack is typically coupled to the CO via a twisted-pair wire. The CO can provide voltage and current to a telephone coupled to the CO via the RJ-11 wire and the RJ-11 jack. For example, known corded phones draw power from the CO during telephone call dialing and during the telephone call. Each RJ-11 jack usually has four wires, which consist of two sets of a tip and ring pair. A single-line corded phone is typically coupled to one set of a tip and ring pair (and can draw power from that tip and ring pair), and a two-line corded phone is typically coupled to each of the two sets of the tip and ring pairs (and can draw power from either or both tip and ring pair).  
         [0008]     As used to describe the background and embodiments of the present invention, the term “coupled” encompasses a direct connection, an indirect connection, or a combination thereof Two devices that are coupled can engage in direct communications, in indirect communications, or a combination thereof Moreover, two devices that are coupled need not be in continuous communication, but can be in communication typically, periodically, intermittently, sporadically, occasionally, and so on. Further, the term “communication” is not limited to direct communication, but also includes indirect communication.  
         [0009]     Cordless phones typically do not draw power from the tip and ring pairs because the cordless phone base is powered by current from an AC outlet. Cordless phones, however, are still connected to one or more of the tip and ring pairs to transmit and receive voice and data communication signals. Moreover, a cordless phone base includes electronic circuitry that is powered at a relatively low voltage as compared to the voltages associated with a tip and ring pair. For example, electronic circuitry is often powered at 12 volts, 5 volts, 3.3 volts, and so on. In contrast, voltages associated with a tip and ring pair can be as high as 350 volts.  
         [0010]     In known telephones, an electronic hook switch consists of a high side switch and a low side switch, so that a low voltage control integrated circuit (“IC”) (e.g., a microcomputer unit, a dialer IC, a specific controller, etc.) can control the electronic hook switch notwithstanding the high voltage between tip and ring. In such known systems, whether or not they are constructed using bipolar transistors or MOSFETs, neither the high side switch nor the low side switch is omitted. Because these systems have both a high side switch and low side switch, there are disadvantageous cost and system design implications.  
         [0011]     For example, known customer premises equipment (“CPE”), such as a telephone, usually employs two Darlington connected PNP transistors to build the high side switch and have one NPN transistor for the low side switch. If P-channel MOSFET is used for the high side switch, an N-channel MOSFET is required for the low side switch to translate the line voltage level to a voltage low enough to interface with the control circuit. Often, each of the low side switch and the high side switch have to withstand voltages as high as 350 volts. In view of the foregoing, it can be appreciated that a substantial need exists for systems and methods that can advantageously provide for an electronic hook switch for customer premises equipment.  
       BRIEF SUMMARY OF THE INVENTION  
       [0012]     Embodiments of the present invention relate to systems and methods for an electronic hook switch for customer premises equipment. In an embodiment, a system includes a first lead configured to be coupled to a tip wire and a second lead configured to be coupled to a ring wire. A diode bridge is coupled to the first lead and the second lead and has a positive output. A low side switch is coupled to the positive output of the diode bridge without a high side switch between the low side switch and the positive output of the diode bridge. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  shows an example of a known telephone line interface circuit.  
         [0014]      FIG. 2  is a system diagram of a telephone line interface circuit in accordance with an embodiment of the present invention.  
         [0015]      FIG. 3  shows an example of a known telephone interface circuit design.  
         [0016]      FIG. 4  is a system diagram of a telephone interface circuit design in accordance with an embodiment of the present invention.  
     
    
       [0017]     Before one or more embodiments of the invention are described in detail, one skilled in the art will appreciate that the invention is not limited in its application to the details of construction, the arrangements of components, and the arrangement of steps set forth in the following detailed description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     According to an embodiment of the present invention, a telephone system includes a telephone line interface circuit that avoids the use of the high side switch in an electronic hook switch circuit. The electronic hook switch can then consist of an NPN transistor or N-channel MOSFET. As a result, space and cost is saved. Because a telephone line interface circuit can be constructed with fewer components, a printed circuit board (“PCB”) or integrated circuit including the electronic hook switch can be of reduced size. Thus, a telephone system (e.g., a cordless telephone base) can be produced and sold at a lower price.  
         [0019]      FIG. 1  shows the block diagram of an example of a known telephone line interface circuit  100 . Telephone network  10  is connected to tip  101  and ring  102 . Protection circuit  103  avoids over voltage damage to the subsequent circuit and diode bridge  104  regulates the line DC voltage to a fix polarity for the remainder of the telephone line interface circuit  100 . If the Microcomputer Unit (MCU)  106  drives the low side switch  105  to on, current ID 1   119  will flow and turn on the high side switch  117 . Then the loop is closed and the loop current will pass through the high side switch  117  and the circuitry behind it. This status is usually called an off-hook condition. In contrast to this off-hook status, if the MCU  106  drives the low side switch  105  to off, current ID 1   119  will no longer flow and the high side switch  117  will be off As a result, the loop is open and no loop current will flow into the circuitry behind the high side switch  117 . This known telephone interface circuit  100  and its operations are representative of how a typical known electronic hook switch is constructed and operates.  
         [0020]     The open loop voltage on the line can be as high as 350 volts. The MCU  106  cannot directly drive the high side switch  117  because it is a low voltage device and cannot withstand a voltage as high as 350 volts. While it is in an off-hook condition, the signal coming in will be extracted by the passive side tone network  118  and amplified by the line in amplifier  112 . Out going signal is amplified by the line out amplifier  111  and fed into the line through the line driven amplifier  107 . With respect to the flow of the loop current, it passes through the high side switch  117  and the line driven amplifier  107  and back to the telephone network  10 . Circuit elements such as the line in amplifier  112 , line out amplifier  111  and the MCU  106  typically need an auxiliary power supply. In some known systems, these circuit elements draw power directly from the telephone network  10 , as is the case in a typical corded phone. Usually, no matter where the power comes from, the power supply circuit  113  will have the same reference ground  121  as the MCU  106 , the low side switch  105  and the amplifier circuit elements  111 ,  112 , and  107 . This is usually required to use an auxiliary power supply and set up a normal signal path. Typically, the reference ground  121  of the telephone line interface circuit  100  is at the negative output of the diode bridge  104 .  
         [0021]      FIG. 2  is a system diagram of a telephone line interface circuit in accordance with an embodiment of the present invention. In an embodiment of the present invention, an improved telephone line interface circuit  200  does not include the high side switch present in known telephone line interface circuits. For example, telephone line interface circuit  200 , as compared to the known telephone line interface circuit  100 , includes all the circuit elements of telephone line interface circuit  100  except the high side switch  117 . Moreover, in an embodiment, the interconnections between the circuit elements of telephone line interface circuit  200  remain substantially the same as the interconnections between the circuit elements of known telephone line interface circuit  100 . Furthermore, in an embodiment, each of the circuit elements of circuit  200  can have same internal design as the corresponding circuit elements in know circuit  100 . According to an embodiment of the present invention, the only changes reflected in circuit  200  as compared to known circuit  100  is that the low side switch  105  is coupled to the positive output of the diode bridge  104 , and the line driven amplifier  107  is coupled to the negative output of the diode bridge  104 . Also, the reference ground  121  is not at the negative output of the diode bridge. In telephone line interface circuit  200 , the loop current passes through the low side switch  105  and the line driven amplifier  107  and back to the telephone network  10  in an off-hook state. In an embodiment, the line driven amplifier is biased by a negative voltage, which can be accomplished a variety of ways. By way of example, for a bipolar solution, the NPN transistor is changed to PNP transistor or vice-versa. The AC signal is coupled by capacitors  109 ,  110 . The voltage across these capacitors  109 ,  110  can increase a few volts because they now block the DC biasing between the negative voltage operated circuit elements  107 ,  108  and the positive voltage operated circuit elements  106 ,  111 , and  112 . In other embodiments of the present invention, however, a low voltage capacitor still can be used.  
         [0022]      FIG. 3  shows an example of a known telephone interface circuit design  300 . The high side switch is formed by the transistors  304  and  308 . The low side switch is formed by transistor  310 , and the line driven amplifier is formed by transistors  301  and  307 . One skilled in the art will appreciate that the current that drives the high side switch is part of the loop current, and that current cannot be set too high otherwise the off-hook DC V-I characteristic may be violated. The current, however, must be large enough to drive the high side switch into saturation. An undesirable condition occurs when the voltage between tip and ring is very low, which can be caused by a parallel phone. Thus, known circuits use a low driven current and a high gain transistor to construct the high side switch. Unfortunately, a high voltage PNP transistor usually has low current gain. As a result, two PNP transistors in Darlington configuration are typically employed to form the switch with enough current gain.  
         [0023]      FIG. 4  is a system diagram of a telephone interface circuit design  400  in accordance with an embodiment of the present invention. As compared to known circuit design  300 , circuit design  400  lacks the two high voltage PNP transistors (i.e., transistors  304 ,  308 ) and high voltage NPN transistor  410  acts as the low side switch. One skilled in the art will appreciate that the current driving transistor  410  is not part of the loop current, but rather comes from the MCU  406  and thus is from the auxiliary power supply. In an embodiment, this is advantageous because the magnitude of the driving current does not affect the DC V-I characteristic, provided that the driving current is high enough to drive the transistor to saturation. Thus, in an embodiment, a high driving current can drive the switch without concerning violating the off-hook DC V-I characteristic and only one NPN transistor is used in the low side switch.  
         [0024]     In the above example of circuit design  400 , as compared to known circuit design  300 , two high voltage PNP transistor are not used and thereby from a manufacturing and cost standpoint are “saved.” Embodiments of the present invention, such as circuit design  400 , have demonstrated that there is little or no impact on the high voltage protection circuit and the whole design passes the UL and FCC part 68 tests.  
         [0025]     Embodiments of the present invention encompass not only telephones but also other Customer Premises Equipment (CPE) that is coupled to the telephone network, such as, but not limited to, answering machines, fax machines, computer modems, and so on. Embodiment of the present invention can be implemented in these CPE and can help reduce production costs. For example, in the example of an integrated circuit that includes a telephone line interface circuit, embodiments of the present invention can reduce chip size and thus the cost of the chip.  
         [0026]     Embodiments of systems and methods for an electronic hook switch for customer premises equipment have been described. In the foregoing description, for purposes of explanation, numerous specific details are set forth to provide a thorough understanding of the present invention. It will be appreciated, however, by one skilled in the art that the present invention may be practiced without these specific details. In other instances, structures and devices are shown in block diagram form. Furthermore, one skilled in the art can readily appreciate that the specific sequences in which methods are presented and performed are illustrative and it is contemplated that the sequences can be varied and still remain within the spirit and scope of the present invention.  
         [0027]     In the foregoing detailed description, systems and methods in accordance with embodiments of the present invention have been described with reference to specific exemplary embodiments. Accordingly, the present specification and figures are to be regarded as illustrative rather than restrictive. The scope of the invention is to be defined by the claims appended hereto, and by their equivalents.