The present invention relates generally to electronic communications technologies. More particularly, the present invention relates to power supply subsystems and methods for their use for communication functions.
It is known in communications systems apparatus for medical facilities and other applications to use multiple-wire, switch-based signaling apparatus to send messages from remote sites such as patient rooms to central sites such as nurses' stations. A typical style of hardware to support such requirements might use a central power source to provide power to indicators located nearby, with electromechanical switches at remote sites providing electrical circuit closure to light lamps or otherwise to cause the central-site indicators to activate. Equivalent functionality can be achieved with remotely located power sources and switches that apply power to lamps or other indicators at a central location. These and other implementations can meet operational requirements, but can have significant shortcomings.
An obvious shortcoming is complexity. While the individual circuits in such systems are simple—commonly referred to as “flashlight” circuits, meaning that they can be as simple as a power supply, a switch, and a light bulb, connected by point-to-point conductors—functional verification can be tedious. In addition, while initial construction of such point-to-point systems requires extensive wiring, upgrading such a system to add functions can in some instances be comparable to initial installation in cost. Although wire pathways may already be established in an installation, it may be necessary, for example, to add as many wires as were originally in place to perform a relatively basic upgrade, in addition to any intended upgrading of terminal devices to support the enhanced functionality.
A significant shortcoming in some existing system types involves reliability. A system with wiring that interconnects power devices, switches, and indicators at separate locations can develop a fault that can remain undetected until an operational failure occurs. For example, an inoperable power supply, a broken wire, or even a burned-out lamp may not be noticed until a patient's request for attention goes unheeded. Automatic or intrinsic fault detection is in many cases nonexistent.
Still further shortcomings in some systems involve excess capability. That is, some systems, able to handle high data rates and high capacities, may be excessively costly or complex when applied to basic tasks. Alternative approaches may preferably provide a desirable balance between signal capacity and cost, for example.
Accordingly, it is desirable to provide a communication method and apparatus that balances simplicity of use, cost-effective implementation, intrinsic reliability, and convenient functional verification.
The above and other features and advantages are achieved in some embodiments by a novel apparatus as herein disclosed. Message transmission from multiple remote stations to a central station can use switching power supply devices as transmitters, with the characteristics of the output signals determined by a few basic components and with operation controlled using basic signal inputs. Such transmitters can send a plurality of messages with simple wiring. Power requirements can be kept low by causing the transmitting devices to substantially shut down except while sending messages.
In accordance with one embodiment of the present invention, a communication device is provided. The communication device includes a switching power supply for use as a transmitter, a first network of power supply level-setting components that determines the characteristics of a first output signal level from the switching power supply, and a second network of power supply level-setting components that determines the characteristics of a second output signal level from the switching power supply. The communication device further includes a first signal input to which application of a first input signal selects between the first and second output signal levels, and a signal return node for the communication device.
In accordance with another embodiment of the present invention, a communication device is provided. The communication device includes a linear power supply for use as a transmitter, a first network of power supply level-setting components that determines the characteristics of a first output signal level from the linear power supply, and a second network of power supply level-setting components that determines the characteristics of a second output signal level from the linear power supply. The communication device further includes a first signal input to which application of a first input signal selects between the first and second output signal levels, and a signal return node for the communication device.
In accordance with another embodiment of the present invention, a communication device is provided that includes means for generating a first direct-current output voltage with respect to a return node. The generating means employs a switching power supply having a power input port, a power output port, and a feedback port. The output voltage at the power output port of the switching power supply is a function of a voltage applied to the power input port and of a feedback signal directed to the feedback port of the switching power supply. The communication device further includes means for establishing a first feedback signal level by establishing an impedance network fed by the output of the switching power supply, which network scales the output of the switching power supply to return a signal to the switching power supply feedback input, the characteristics of which scaled signal direct a specific first output level from the switching power supply. The communication device further includes means for altering the first feedback signal level to form a second feedback signal level by switchably modifying the impedance network, whereby the feedback port has the second feedback signal level impressed thereon in place of the first feedback signal level. The communication device further includes means for reversing a state of a switch, whereby the impedance network is modified, and whereby a second direct-current output voltage for the communication device is directed in place of the first direct-current output voltage.
In accordance with another embodiment of the present invention, a communication method is provided, comprising the steps of outputting a first output voltage using a voltage regulator, dividing the first output voltage with a divider network to form a feedback signal intermediate in magnitude between the output voltage and a return node voltage, directing the feedback signal back into a feedback input of the voltage regulator to establish a first output baseline level, and dynamically altering the ratio in the divider network to change the first output voltage to a second output voltage.
There have thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described below and which will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract included below, are for the purpose of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be used as a basis for the designing of other structures, methods, and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.
The invention will now be described with reference to the drawing figures, in which like reference numerals refer to like parts throughout. A preferred embodiment in accordance with the present invention provides a transmitter that uses a switching power supply integrated circuit as a transmitter.
Switching power supply technology is well enough established that most or all of a set of core functions of such a device can be embodied in a single, low-cost, monolithic integrated circuit (IC) device. Core functions for some switching power supply ICs include at least: an oscillator to establish a switching rate, which may be externally adjustable or triggerable; a reference voltage generator to permit output scaling; a pass transistor capable of conducting at least some input power to an output; and a ramp generator and comparator circuit to determine for each oscillator cycle the time duration for which the pass transistor needs to remain in the “on” state to maintain the output level. Many such ICs can implement bucking or boosting functions—or both—and can support voltage multiplication, inversion, current sourcing, current sinking, and other functions through the addition of external components.
The return node 24 is shown by a specific style of ground symbol. All such “grounds” shown herein represent a common electrical potential within the limits of ordinary electrical wiring and circuit board track conductivity. It is to be understood that the “ground” shown does not necessarily correspond to earth ground, chassis ground, or any other connection external to the device being described, but is limited except as noted to provision of a zero-volt reference for the transmitter 10 being disclosed.
For simplicity in explanation, it will be assumed that the switching power supply IC 12 is, as a minimum, suitable for accepting, at an input port 14, a voltage that supplies direct current (DC) with positive polarity, and for outputting, at an output port 18, a lower positive DC voltage (closer to ground). It is to be understood that a range of devices suitable for the switching power supply IC 12 may also be capable of generating an output higher than the input, generating multiple outputs, or generating an output of opposite polarity from the input, while still other devices may accept negative DC input or alternating current (AC) input.
It is further to be understood that the device shown as a monolithic IC 12 in
The capacitor, resistors, diodes, and switches shown in the figures may preferably be types conforming to the following characteristics.
The capacitor may be a ceramic, electrolytic, or other common type with suitable capacitance, tolerance, temperature, equivalent series resistance (ESR), and voltage ratings. While a single capacitor is shown, the performance required may be achieved by interconnection of multiple devices. A large electrolytic capacitor with high ESR, for example, may preferably be bypassed with a small, low-ESR device if needed.
The resistors may in some embodiments be of composition, film, wire wound, or other types available in the resistances, tolerances, and reliability and power ratings required for the application.
The diodes are preferably reverse breakdown types, also referred to in the literature as avalanche, regulator, reference, and zener diodes, depending in part on the details of the mechanism by which their properties are achieved. The diodes described herein preferably have knee voltages and power ratings appropriate to the application. Single diodes are shown, but strings of diodes may be preferred to achieve specific voltage levels without recourse to a multiplicity of types, and monolithic arrays of diodes may be preferred to discrete units.
The switches are preferably electronic devices such as field effect transistors (FETs) that can be switched from being highly conductive to being largely nonconductive using logic-level control input signals. On-state resistance values of available FET switches range from a few hundred ohms to a fraction of an ohm, while off-state resistances are commonly many megohms. Typical FET switches are bidirectional (i.e., have largely symmetrical current carrying properties when either terminal of the switched path is more positive) and may be packaged in multiples in monolithic ICs that can include control and protection circuitry.
Electromechanical switches, such as sensitive switches, proximity switches, relays, and the like may represent acceptable alternative embodiments for at least one of the electronic switches described herein.
A control input to the preferred switching power supply IC 12, termed Output Enable 28, is active low. That is, applying an electrical signal that is more positive than the ground reference by an amount corresponding to a logic “1” in TTL or CMOS logic, for example, causes the IC to halt operation, while applying an electrical signal near the ground reference, corresponding to a logic “0” in TTL or CMOS logic, for example, allows the IC to operate.
R3, a third resistor 30, is configured in parallel with R2, connected to ground on the low side and connected on the opposite side to the R1−R2 junction 22 via SW2A, an electrically-operated switch 32. R4, a fourth resistor 34, is connected to ground on its low side and connected via SW1, another electrically-operated switch 36, to the power supply IC output terminal 18. The power supply IC output terminal 18 has an additional load to ground consisting of SW2B, another electrically-operated switch 38, in series with R5, a fifth resistor 40, and ZD1, a reverse breakdown diode 42. C1, a capacitor 44, functions as an output filter and charge storage device.
With all three electrically-operated switches 32, 36, and 38 set in their substantially nonconductive state and the Output Enable 28 signal set active low, the switching power supply IC 12 accepts input power on its input terminal 14 and generates an output voltage on terminal 18 that is divided by the resistors R1 and R2 to generate a feedback signal 26 that regulates the output voltage of the switching power supply IC 12.
The foregoing describes a nominal configuration for a switching power supply that uses a monolithic IC and minimal external components, plus the switching control apparatus disclosed herein. Other circuit configurations are possible, and may add, for example, input and output inductors to the input and output terminals 14 and 18, respectively, as well as various combinations of output pass transistors to carry most of a high-power switching power supply IC's output current external to the IC. When the switching power supply IC 12 is used as part of a relatively low power communications device, most of these additional components may preferably be omitted, as shown in
As indicated above, for the schematic of
Switching power supply IC 12 devices use a resistive-divider configuration for establishing feedback voltage. Here, a feedback voltage would be scaled to R2/(R1+R2), for example with a built-in voltage reference in the IC 12 used to control circuit operation. Adding R3 (and omitting the resistance in SW2A switch 32, which omission is appropriate for many contemporary electronic switch types) changes the feedback scaling to (R2∥R3)/(R1+R2∥R3). If resistor R3 (in series with the first switch 32) is appropriately selected, then the final output signal voltage can be approximately V0/2, if desired. Since the expressions given include two equations in four unknowns, it is possible to select both V0 and one of the resistors, then to solve the equations for the remaining unknowns. This will generally allow the output voltage range and the resistance range to be chosen, with the remaining resistors computed to satisfy the equations. A different IC 12 type with a different feedback circuit would require an analogous design process as determined by manufacturer specifications for that type.
A second effect of changing the state of INB 46 in the circuit of
Raising input signal INA 48 in
Pulling INA 48 low substantially reverses the above process, with current from the IC 12 driving the output to either V0 or V0/2, as determined by the state of INB 46 when INA 48 is changed. Similarly, reversing INB 46 when INA 48 is active low causes charge from the IC 12 to drive the output from V0/2 to V0 at a rate controlled by circuit properties such as the output drive characteristics of the IC 12 and the capacitance of the capacitor 44, the transmission line, and any receiver load. The rising edge timing characteristics of the output signal 18 are determined by factors including the source impedance of the power source feeding the switching power supply IC 12 and the drive circuitry in the IC 12. For example, if the IC 12 includes a substantially conventional operational amplifier in the output section thereof, the effective dynamic output impedance of the IC 12 may be as low as or less than a few ohms.
The invention is capable of transmitting data at a rate related to several characteristics of the specific embodiment. For example, slewing from V0 to V0/2 occurs with the switching power supply IC 12 momentarily cut off, so that the slew rate is a function of the total energy storage in the transmission line to the receiver, including lumped and distributed capacitances and inductances, and the resistance of the resistor R5. Slewing from V0/2 to V0, by contrast, occurs at a rate controlled by the ability of the IC 12 to pump charge into the transmission line. Since the IC 12 employs a switching circuit, charge is pumped into the transmission line during only a part of each cycle of the IC 12 for typical switching power supply ICs. The output capacitor 44 may reduce switch rate ripple in the output, in exchange for reducing the maximum slew rate. Thus the data rate limit in a transmitter using the invention depends on output circuit impedance from all sources, drive capability of the switching power supply IC 12, and the switching rate of the IC 12.
Detection of the transmitted signal requires that the detector be able to discriminate between the states, so the receiving circuit may preferably include a threshold detection circuit at least as fast as the maximum applied data rate. In sampled applications, Nyquist criteria may apply, so that the receiver should sample the signal line at least twice as fast as the data rate used in the application.
System data rate will thus be determined in part by factors such as transmission line characteristic impedance, unit capacitance and inductance, length, and termination style, as well as driver IC 12 properties such as clock frequency. Like other communication systems, the inventive apparatus requires an application specification to guide users regarding maximum data rate as a function of circuit and transmission line characteristics.
If R3 30 and SW2A 32 are configured across R1 16 instead of R2 20, then the feedback level when SW2A 32 is on will typically be more positive than when SW2A 32 is off. In that configuration, it may be preferable for SW2B 38 to be fed via a logic inverter, or to be of a type that is conductive when its input is low. Then the output states for INB 46 will be reversed from those indicated above, and V0 will preferably be computed based on the ratio R2/(R2+R1∥R3), with V0/2 based on R2/(R1+R2).
The resistor values determine the output levels, which may preferably be selected so that a receiver can distinguish between them accurately with a variety of interconnecting cable lengths. Thus, when INB 46 is active and INC 52 is inactive, R2 20 and R3 30 in parallel set the feedback node 26's level, and thus the output level 18 of the transmitter 50. When INC 52 is active and INB 46 is inactive, R2 20 and R6 62 are in parallel instead. When both INC 52 and INB 46 are active, all three resistors R2 20, R3 30, and R6 62 are in parallel. Properly chosen resistor values can assure that all of the resistor combinations define distinct and detectable levels.
In switching from V0 to the state in which INC 52 alone is active, the three elements of SW3, 56, 58, and 60, are activated. As noted, this causes the switching power supply 50 to shift to another, lower, level. At the same time, a circuit similar to that of SW2B 38 and ZD1 42 is activated to increase switching speed. In this mode, SW3C 60 conducts, connecting the output 18 to ZD3 66 through R5 40. ZD3 66 is preferably a reverse breakdown diode with a voltage nominally equal to the intended output 18, so that it will draw current approximately until the output signal 18 reaches its final value. It is to be noted that the use of a single resistor R5 40 to draw all falling-edge current is optional, and other configurations, such as one in which each of the diode-and-switch combinations would have a separate resistor, are equally valid electrically and may be preferred for some embodiments.
In order to switch from any higher output 18 voltage to the lowest voltage, both INB 46 and INC 52 must be active. This activates both switches SW2C 54 and SW3B 58, so that diode ZD2 64 can draw current. Note that both ZD1 42 and ZD3 66 can be active until the output signal 18 drops below their respective breakdown voltages. Once the final voltage is reached, all three diodes are inactive.
The 4-state arrangement described can be extended to any number of distinct levels, although binary multiples may be preferred. A receiver for a multiple-level transmitter 50 embodiment may have, for example, multiple analog comparators or an analog-to-digital converter to detect the various levels and determine the corresponding combinations of logic states. If each of a multiplicity of transmitters is directly wired to a separate input channel in a receiver, which connectivity may be facilitated using an analog multiplexer, for example, then the received signal for each channel can be scaled to account for differing wire lengths, tolerances in individual resistor values, and other variations between transmitters before or after being decoded from a voltage level to a logic combination.
The invention is shown using a switching power supply, a term that describes a general class of devices that preferably use a DC input to create a DC output, where the input may be poorly regulated and the output regulation is typically quite good, although the presence of some output ripple at the switching rate is common. The presence of significant artifacts (i.e., switch rate ripple and its harmonics as well as noise passthrough from the DC input power, which may include ripple at the frequency of the facility power AC, for example) in the transmitted signal may have little effect on circuit function provided the receiver includes filtering, averaging, or hysteresis appropriate to the amplitude of the artifacts.
Use of a switching power supply is generally desirable, since contemporary switching power supply ICs can achieve high efficiency, which translates to minimal dissipated power within the power supply itself. However, it is also possible in the present invention to use an adjustable linear regulator in place of the switching power supply IC, where decreased efficiency may be offset by other considerations. In particular, high efficiency in switching power supply applications is most noticeably achieved near the maximum output of which a given supply is capable. Thus, since the present invention preferably consumes low total power, design for high efficiency at low total output is appropriate, but a relatively inefficient linear regulator may be acceptable.
In using a linear regulator for a transmitter 70, as shown in
It may also be preferred in some embodiments to use an AC circuit instead of DC, which may be facilitated by using back-to-back or double-ended diodes in place of the single diodes shown for ZD1, ZD2, and ZD3 to allow the output to swing both positive and negative with respect to the ground reference. Use of AC can allow transformer isolation and other options to be included. An AC signal receiver preferably uses rectification and filtering, Nyquist-rate sampling, or another satisfactory AC measurement technique to sense signal magnitude.
In a specific case described in a U.S. patent application entitled, “VOLTAGE ISOLATED DETECTION APPARATUS AND METHOD,” filed Aug. 27, 2004, having U.S. patent application Ser. No. 10/926,994, a call cord for use with a wall-mounted medical facility communication device can be unplugged or plugged in, and has a single button on it that can be pressed by a patient. If the unplugged/plugged status and the button belong to electrical circuits generating signals, then the unplugged/plugged signal and the pressed signal described in the above-referenced patent application can be connected, in one mode of use, to INA 48 and INB 46, respectively, in
For both the
Upgrading from a
Although the switching power supply IC-based transmitter shown is useful in support of medical facility messaging, it can also be used in other environments such as manufacturing, warehousing, and office environments where low power or low cost may be a principal consideration.
The many features and advantages of the invention are apparent from the detailed specification, and, thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to that fall within the scope of the invention.