Power efficient driver architecture

Disclosed are various embodiments for providing a power-efficient driver architecture supporting rail-to-rail operation in full duplex mode. A driver is configured to drive a duplex signal over a transmission medium. A hybrid is configured to recover a received signal from the duplex signal. The received signal is generated by a remote transceiver. The driver is configured to drive the duplex signal based at least in part on the received signal recovered by the hybrid.

BACKGROUND

Compared with newer forms of Ethernet, 10Base-T Ethernet employs a greater line voltage swing of 5.0 V at the line driver. 100Base-T Ethernet employs a line voltage swing of 2.0 V, while 1000Base-T Ethernet employs a line voltage swing of 4.0 V. To handle these different characteristics, a multi-mode Ethernet transceiver may employ multiple line drivers. Such line drivers may be current-mode line drivers and/or voltage-mode line drivers.

A current-mode line driver may correspond to a Norton equivalent circuit having a floating current source. Since the current source is high impedance, the output impedance of the driver may be formed by a termination resistance in parallel with the load. The current used by a current-mode line driver may be high because the impedance seen by the current source is the termination impedance in parallel with the load impedance. For example, half of the current may be consumed by the termination impedance. Thus, more current is required to create the voltage swing across the load that terminates the line at the remote end.

By contrast, with a voltage-mode line driver, a differential voltage source may drive the line with a very low impedance. The local termination impedance may be in series connection with the voltage source and may consume, for example, half of the voltage drop of the voltage source. Compared to the voltage-mode line driver, the current-mode line driver may be driven from lower supply voltages and may be easier to implement but may consume more power.

DETAILED DESCRIPTION

The present disclosure relates to a power-efficient line driver architecture using merged duplex currents. The line driver architecture may provide class B (or class AB) rail-to-rail operation for full-duplex transmissions. Previous line drivers are less power efficient because of overhead in dealing with the duplex currents (e.g., transmit and receive signals) separately. Further, previous line drivers employ additional output voltage headroom to maintain linear operation in scenarios where both transmit voltage and receive voltage are at their maximum values. By contrast, with rail-to-rail operation, the voltage swings from the maximum available voltage (e.g., the supply voltage) to the minimum available voltage (e.g., the ground voltage). Rail-to-rail operation leads to lower power consumption in comparison to drivers employing additional output voltage headroom.

In addition, some multi-mode Ethernet transceivers may have utilized multiple line drivers to accommodate the various modes. For example, previous multi-mode Ethernet transceivers may have included a voltage-mode line driver for one or more modes and a current-mode line driver for one or more other modes. The line driver architecture described herein provides power efficient operation while in current mode, which may be used to simplify transceiver designs that previously employed multiple line drivers. Also, voltage-mode line drivers may use relatively high supply voltages, while the current-mode line driver described herein supports process scaling with rail-to-rail operation.

FIG. 1is a block diagram illustrating an exemplary duplex communication system100. The duplex communication system100includes a transceiver103, a transmission medium106, and a remote transceiver109. In the duplex communication system100, a full-duplex mode of operation may be supported where the transceiver103and the remote transceiver109are able to communicate simultaneously over the same transmission medium106. The duplex communication system100may correspond to Ethernet communication, digital subscriber line (DSL) communication, cable modem communication, and/or other systems of communication which may be wired or wireless. The transmission medium106may correspond to wired electrical transmission media such as, for example, twisted-pair, coaxial cable, etc. In the example ofFIG. 1, a pair of transformers112aand112bmay provide electrical common mode isolation at the ends of the transmission medium106.

Although the present disclosure discusses electrical signals in the forms of analog current and voltage, it is understood that the principles of the present disclosure may be extended to electromagnetic wave-based signals, such as radio-frequency signals, infrared signals, optical signals, and so on involving modulation of light intensity or electromagnetic fields. Thus, the transmission medium106may include optical transmission media such as fiber optics, etc. and/or wireless transmission media that carry signals such as radio-frequency waves, infrared, etc.

The transceiver103may include, for example, a current source115, a load impedance (Rload)118, a hybrid121, a hybrid current source124, and other components. The remote transceiver109may include, for example, a current source127, a load impedance (Rload)130, a hybrid133, a hybrid current source136, and other components. The remote transceiver109may or may not be a mirror of the transceiver103. The transmitted signal generated by the transceiver103is denoted as itx(current) or Vtx(voltage), and the received signal generated by the remote transceiver109is denoted as irx(current) or Vrx(voltage) inFIG. 1. The relationships between current and voltage are irx=Vrx/Rloadand itx=Vtx/Rload.

In the example ofFIG. 1, the current source115is configured to provide current of 2×itxto account for the maximum current seen across Rload118, which is itxirx. Similarly, the current source127is configured to provide current of 2×irxto account for the maximum current seen across Rload130, which is itx+irx. Each of the supply voltages also doubles, which results in a quadrupled power consumption relative to power consumption associated with the transmitted signal itself without duplex operation. The duplex output signal on the transmission medium106is denoted by ioor Vo. The output voltage Vocorresponds to the sum Vtx+Vrx. The output current iocorresponds to the difference itx−irx.

The hybrid121is configured to recover the received signal Vrxfrom the duplex signal Vo. Because the hybrid121has access to the locally-generated transmitted signal, the hybrid121is configured to cancel the transmitted signal from the duplex signal, thus recovering the received signal. The hybrid121includes a hybrid current source124, which produces a current of itx/m, which is a small replica of the locally generated transmitted signal. The factor m is chosen to reduce current consumption.

The hybrid133is configured to recover the transmitted signal Vtxfrom the duplex signal Vo. Because the hybrid133has access to the locally-generated received signal, the hybrid133is configured to cancel the received signal from the duplex signal, thus recovering the transmitted signal. The hybrid133includes a hybrid current source136, which produces a current of irx/m.

FIG. 2is a block diagram illustrating another exemplary duplex communication system200according to an embodiment of the present disclosure. The duplex communication system200includes a transceiver203, a transmission medium206, and a remote transceiver209. In the duplex communication system200, a full-duplex mode of operation may be supported where the transceiver203and the remote transceiver209are able to communicate simultaneously over the same transmission medium206. The duplex communication system200may correspond to Ethernet communication, digital subscriber line (DSL) communication, cable modem communication, and/or other systems of communication which may be wired or wireless. The transmission medium206may correspond to wired transmission media such as, for example, twisted-pair, coaxial cable, fiber optic cable, etc., or wireless transmission media that carry signals such as radio-frequency waves, infrared, etc. A pair of transformers112(FIG. 1) may provide electrical common mode isolation at the ends of the transmission medium206.

The duplex output signal on the transmission medium206is denoted by ioor Vo. The output voltage Vocorresponds to the sum of the transmitted signal Vtxplus the received signal Vrx. The output current iocorresponds to the difference between the transmitted current itxand the received current irx.

The remote transceiver209may be the same as or different from the transceiver203. In one embodiment, the remote transceiver209may correspond to the remote transceiver109(FIG. 1). As shown in this example, the remote transceiver209may include a current source212producing a current of 2×irxand a load impedance (Rload)215. The remote transceiver209may also include a hybrid133(FIG. 1) and additional circuitry not shown.

The transceiver203includes a current-mode digital-to-analog converter (IDAC)218, a voltage-controlled current source221, a hybrid224, and other components. The IDAC218takes as input a digital data signal225and generates a transmitted signal itx/m, where m may be much greater than 1, e.g., 10 or some other factor. The hybrid224is used to recover the received signal from the duplex signal present on the transmission medium206. The hybrid impedance (Rhybrid)226may be much greater than the load impedance (Rload) of the transceiver203at the voltage-controlled current source221. The hybrid224produces the received signal Vrx227with some attenuation and a control signal Vc, which is the control input to the voltage-controlled current source221.

The voltage-controlled current source221may be a Gm cell having the Gm value of k/Rload, where k=2 or another value. The control signal Vccorresponds to the difference between the transmitted voltage and the received voltage Vtx−Vrx, divided by a constant factor k, e.g., where k=2 or another value. The control signal Vcis extracted from Voby superimposing Vtx=itx×Rloadon −Vo/2 at the hybrid224port (cp, cn). The received signal input Vrx227is readily available from the differential nodes where Vtxnulls on the hybrid224resistor string.

The architecture depicted inFIG. 2enables full-duplex drivers that approach the fundamental limit in power efficiency through the use of rail-to-rail voltage swings and partial cancellation of duplex currents. The voltage-controlled current source221may use a class B or class AB output stage to source iodirectly from the power supply. Under the architecture shown inFIG. 2, no extra voltage headroom is used in the class B or class AB output stage at the maximum voltage swing when Vtx=Vrx=Vmaxand io=(Vtx−Vrx)/Rload=0. As a result, the voltage-controlled current source221may eliminate the overhead of dealing with the duplex currents separately and may enable power efficient rail-to-rail operation.

A class B output stage using two transistor devices in a push-pull arrangement may offer excellent power efficiency. However, class B output stages may also suffer from crossover distortion resulting from switching from one device to another. In some cases, a class AB output stage may be used instead. A class AB output stage employs a small quiescent current so that the devices are not completely off when they are not in use. Consequently, class AB stages sacrifice some power efficiency in favor of linearity.

FIG. 3shows a circuit-level diagram showing one example implementation of the exemplary duplex communication system200(FIG. 2) according to an embodiment of the present disclosure. The duplex communication system200includes a transceiver203, a transmission medium206, and a remote transceiver209as inFIG. 2. The transceiver203includes an IDAC218, a voltage-controlled current source221as a driver, a hybrid224, and other components.

The hybrid224is depicted with resistors230,233,236,239,242, and245in an exemplary arrangement. Although discussed as being resistors, such resistors may correspond to other components having impedance values. In one example, the resistors230and233may have the values (k+2)/4×m×Rload, the resistors236and242may have the values (⅓)×(k+2)/4×m×Rload, and the resistors239and245may have the values (⅔)×(k+2)/4×m×Rload, where k=2 or another factor. The received voltage Vrx+ is split off between the resistors236and239, while the received voltage Vrx− is split off between the resistors242and245. A hybrid current ihflows from resistor245to output port on and a hybrid current ihflows from resistor239to output port op. The value of ihmay be close to zero and negligible.

For applications depending on output linearity, the voltage-controlled current source221may comprise closed-loop voltage buffers251,254driving a replica load resistance255of (m/k)×Rload, and current mirrors257,260amplifying and copying a small replica current im=Vc/[(m/k)×Rload]=io/m flowing through this resistance255to the load Rload215. As inFIG. 2, the current mirror gain m may be selected to be much greater than 1, e.g., 10 or another value. The class B or class AB output stages of the voltage-controlled current source221, which correspond to the current mirrors257,260, may form an H-bridge driver topology featuring active termination intrinsically and rail-to-rail operation in full-duplex mode.

It is noted that the operation of the transceiver203may be reconfigured for multiple different physical medium dependent (PMD) modes using the same driver circuitry depicted inFIGS. 2 and 3. Such different PMD modes may use different voltage swings. For example, the same driver circuitry may be configured to support 10Base-T Ethernet or 1000Base-T Ethernet as desired.

FIG. 4is a flowchart illustrating one example of functionality implemented in a transceiver203in the exemplary duplex communication system200(FIG. 2) according to an embodiment of the present disclosure. It is understood that the flowchart ofFIG. 4provides merely an example of the many different types of functional arrangements that may be employed to implement the operation of the transceiver203as described herein.

Beginning with reference numeral403, the transceiver203generates a transmitted signal from a digital data signal225(FIG. 2) using a digital-to-analog converter such as an IDAC218(FIG. 2). In reference numeral406, the transceiver203drives the duplex signal over a transmission medium206(FIG. 2) using a driver including a voltage-controlled current source221(FIG. 2) based at least in part on the transmitted signal.

In reference numeral409, the transceiver203recovers a received signal, generated by a remote transceiver209(FIG. 2), from the duplex voltage signal using a hybrid224(FIG. 2). In reference numeral412, the transceiver203drives the duplex current signal over the transmission medium206based at least in part on the received signal recovered by the hybrid224and the transmitted signal generated by the IDAC218. Thereafter, the operation of the transceiver203depicted in the flowchart ends.