1. Field of the Invention
The present invention generally relates to telecommunications circuitry, and more particularly to a circuit that controls the application of power to a line driver circuit.
2. Discussion of the Related Art
In recent years telephone communication systems have expanded from traditional plain old telephone system (POTS) communications to include high-speed data communications as well. As is known, POTS communications includes not only the transmission of voice information, but also PSTN (public switched telephone network) modem information, control signals, and other information that is transmitted in the POTS bandwidth, which extends from approximately DC to approximately 3.4 kilohertz.
New, high-speed data communications provided over digital subscriber lines, such as Asymmetric Digital Subscriber Line (ADSL), Rate Adaptive Digital Subscriber Line (RADSL), etc. (more broadly denoted as xDSL) provide for high speed data transmissions, as is commonly used in communicating over the Internet. As is known, the bandwidth for xDSL transmissions is generally defined by a lower cutoff frequency of approximately 30 kilohertz, and a higher cutoff frequency which varies depending upon the particular technology. Since the POTS and xDSL signals are defined by isolated frequency bands, both signals may be transmitted over the same two-wire loop.
A xe2x80x9cline-card,xe2x80x9d containing line interface circuitry, is provided at the central office. The line interface circuitry provides the interconnections among xDSL circuitry, POTS or PSTN voice circuitry, off-hook (or tip/ring) detection circuitry, ring generator circuitry, and the local loop. The line interface circuitry also includes appropriate electronic filtering circuitry that operates to minimize any noise transmission across the local loop. As is known, the line interface circuitry includes a POTS filter that is interposed between the various POTS circuits and the xDSL circuit. This filter protects the POTS circuitry from the high frequency signals of the xDSL transmission circuitry. It also serves to minimize noise transmissions across the local loop from the central office to the customer premises.
As is known, a central office typically includes numerous line cards to service a number of local loops. Each line card includes a line driver circuit that drives signals across the local loop. It should be appreciated that, for any given local loop, the line driver spends a significant percentage of time in standby operation (ie., not transmitting). During this xe2x80x9cstandbyxe2x80x9d time, however, the line driver circuit continues to consume power. Although the power consumed by a single line driver circuit is relatively small (often on the order of approximately 30 mAmps), this power consumption, multiplied by the large number of line drivers in a central office location, realizes a relatively large overall power consumption.
Accordingly, there is a desire to provide line driver circuitry that dissipates less power than line driver circuitry known in the prior art.
Certain objects, advantages and novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve certain advantages and novel features, the present invention is generally directed to a power control circuit for a line driver circuit in a central office. In a broad sense, the present invention operates to power-down line driver circuitry when it is not in use, and apply power to the line driver circuitry when transmissions are requested by a customer (e.g., customer premises). This reduces the power consumption of the line driver by eliminating the quiescent current draw when the line driver is idle. Recognizing that the typical line driver is in an idle state the vast majority of the time, compounded by the vast number of line drivers that exist within a central office environment, it will be appreciated that the overall power savings may be tremendous.
In accordance with one aspect of the invention a circuit is provided for controllably applying power to a line driver. The circuit includes an isolation circuit disposed to receive a power control signal, the isolation circuit configured to generate a pair of output signals that are electrically isolated from the power control signal, each of the output signals having a state that is determined by the power control signal. The circuit also includes a power application circuit having a first and second input and a first and second output, wherein the first input is coupled to a first output of the isolation circuit and the second input is coupled to a second output of the isolation circuit, and wherein the first output is disposed to be coupled to a positive power input of the line driver and the second is disposed to be coupled to a negative power input of the line driver.
In accordance with the preferred embodiment, circuit includes a first optocoupler comprising a first light emitting diode and a first phototransistor disposed to sense emissions from the first light emitting diode, wherein the first light emitting diode is configured to receive an input power control signal. The circuit also includes a second optocoupler comprising a second light emitting diode and a second phototransistor disposed to sense emissions from the second light emitting diode, wherein the second light emitting diode is series-connected with the first light emitting diode between the input power control signal and ground. The circuit also includes a p-channel MOSFET having a source node coupled to a positive power supply, the p-channel MOSFET having a gate node coupled to an output of the first phototransistor, and the p-channel MOSFET having a drain output coupled to a positive power input of the line driver. The circuit includes a n-channel MOSFET having a source node coupled to a negative power supply, the n-channel MOSFET having a gate node coupled to an output of the second phototransistor, and the n-channel MOSFET having a drain output coupled to a negative power input of the line driver. The circuit further includes a first voltage control circuit coupled to the gate node of the p-channel MOSFET, the first voltage control circuit configured to turn the p-channel MOSFET off when the first optocoupler is turned on, the first voltage control circuit configured to turn the p-channel MOSFET on when the first optocoupler is turned off Finally, the circuit includes a second voltage control circuit coupled to the gate node of the n-channel MOSFET, the second voltage control circuit configured to turn the n-channel MOSFET off when the second optocoupler is turned on, the second voltage control circuit configured to turn the n-channel MOSFET on when the second optocoupler is turned off.
In accordance with another aspect of the invention, a system is provided for controllably applying power to a line driver. The system includes a line driver circuit at a central office having a first and second output signal configured to transmit a differential transmission signal to a customer premises over a local loop. The system also includes an impedance matching circuit disposed at an output of the line driver circuit and configured to maintain a low impedance of conductors within the local loop. The system further includes a start-up control circuit coupled to the local loop and configured to sense signal activity over the local loop. Finally, the system includes a power application control circuit coupled to the line driver circuit and configured to control the application of power signals to the line driver circuit, in response to the start-up control circuit.
In accordance with another aspect of the invention, a method is provided for controlling the application of power to a line driver. The method includes the steps of sensing a request from a customer premises for a transmission exchange across a local loop and applying power to a line driver circuit, in response to the request for transmission. In addition, the method includes the steps of determining when the transmission exchange has terminated, and terminating the application of power to the line driver circuit.