The invention relates to a line terminator, and, more particularly, to a line terminator having an electronic voltage regulator with an improvement in noise reduction.

A line terminator includes a voltage regulator of semiconductor construction that is available from a manufacturer as an item of commerce. The purpose of the voltage regulator is to provide a source of voltage at a nominal value, within controlled limits of variation from the nominal value. The voltage regulator is a circuit component combined with other circuit components of an electronic circuit on a circuit board. A circuit designer selects the manufacturer to supply a voltage regulator that is compatible with the circuit that is being designed by the circuit designer. The voltage regulator is supplied as a semiconductor package having multiple electrical leads. These electrical leads are soldered to conducting pads or conducting paths on an outer side of a circuit board. The semiconductor package provides an integrated circuit that integrates the voltage regulator with auxiliary electronic circuits having auxiliary functions. For example, the integrated circuit is constructed with circuit components having the functions of, current limiting and thermal limiting, which protect the voltage regulator from damage.

A primary problem faced by a circuit designer is caused by the presence of unwanted noise, in the form of unwanted voltage spikes and various low level voltage fluctuations. This noise is induced by emanating electrical energy. The electrical energy is transmitted, either by radiation through the air, or by transmission along the circuit from the electrical components while they operate. The circuit is inherently inductive, which allows the unwanted electrical energy to induce the unwanted voltage

fluctuations in the circuit. One technique for combatting the noise, is to combine the voltage regulator with a noise reduction circuit. The noise reduction circuit is designed by the circuit designer, and is coupled to selected electrical leads on the voltage regulator. For example, a noise reduction circuit utilizes a capacitor to compensate for inherent inductance of the circuit. However, a demand exists for voltage regulators with more closely confined limits of nominal voltage, which renders less effective the use of a capacitor for noise reduction.

The invention resides in a line terminator comprising a voltage regulator combined with a voltage divider circuit and a noise reduction circuit path in which noise reduction on the circuit path is apportioned along the entire length of the circuit path.

An embodiment resides in a line terminator comprising a voltage regulator combined with a voltage divider circuit and a noise reduction circuit constructed with a circuit path in which noise reduction on the circuit path is apportioned to extend equally between a pair of spaced apart capacitors.

An embodiment comprises, a voltage regulator, and a voltage divider circuit on a circuit board, both coupled to an input circuit path for supplying input voltage, wherein the input circuit path has a path length extending on the circuit board that is apportioned to extend equally between a pair of spaced apart capacitors. An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, according to which:

FIGURE 1 is a plan view of one side of a circuit board illustrating linear circuits;

FIGURE 2 is a view similar to Fig. 1, illustrating circuit components mounted on the circuit board and connected electrically to the circuits;

FIGURE 3 is a bottom plan view of the circuit board shown in Fig. 1, together with an electrical connector; FIGURE 4 is a side view of the electrical connector shown in Fig. 3, prior to mounting on the circuit board shown in Fig. 3;

FIGURE 5 is a view similar to Fig. 3, showing the circuit board without the connector;

FIGURE 6 is a schematic view of an electrical circuit provided by the structure shown in Fig. 2;

FIGURE 7 is a fragmentary view of a portion of the circuit board as shown in Fig. 1, together with a voltage regulator.

With reference to Figs. 2 and 6, an electrical line terminator 1, Fig. 2, is constructed as an electrical circuit to correspond with the schematic circuit shown in Fig. 6. A voltage regulator 2 comprises an integrated circuit of semiconductor construction having four electrical leads 3, 4, 5, 6. For example, the voltage regulator 2 is commercially available as part number REG1117-2.85 from the manufacturer, Burr-Brown Co. , Tucson, Arizona. An alternate source of supply is identified as part number LT1117CST-2.Θ5 from Linear Technology , Mulpitas, California. The terminal 3 of the voltage regulator 2 is referenced at a voltage V-in in the schematic view of Fig. 6. The terminal 3 is connected to a conducting circuit path 7 on a circuit board 8 that connects to four plating lined holes 9 through the circuit board 8.

With reference to Fig. 2, a noise reduction capacitor Cl, 10 is connected on a wide, enlarged circuit path 11 between input term power and ground at 12, or earth electrical potential. For example,

Capacitor Cl is commercially available as part number

293D475X0016B2T, from Sprague Electric Company, Sanford Maine, rated at 16 Volts DC, having a capacitance of 4.7 microFarads.

In Fig. 2, the circuit path 11 extends from Cl to connect with fifteen plating lined holes 13 through the circuit board 8. The plating lined holes 13 are referenced to ground at 12. The lead 5 on the voltage regulator 2 is connected, Fig. 2, to a wide, enlarged circuit path 14 referenced to ground at 12. The circuit path 14 is connected to fifteen plating lined holes 15 through the circuit board 8. The plating lined holes 15 are referenced to ground at 12.

With reference to Fig. 6, thirteen, multiple resistors Rl-R-13 are bussed, or connected, to a single electrical circuit pad or path 16. With reference to

Fig. 2, the electrical pad 16 is on a conductive circuit path 17, and is referenced to a voltage V-out, Fig. 6, which is the output voltage of the voltage regulator. The output voltage is at a nominal value within controlled limits of the nominal value. A requirement of the terminator 1 is to reduce unwanted noise in the circuit path 17. The presence of unwanted noise will cause unwanted variations in the output voltage, V-out. A feature of the embodiment resides in the circuit path 17 circumscribing the remainder of the circuit that comprises the terminator 1, to shield the circuit from emanating electrical energy, and then providing for noise reduction on the circuit path 17, in a manner to be described, hereafter. A first resistor network 18, Fig. 2, comprises a package containing the multiple resistors R1-R13. The resistors within the resistor network 18 each are connected between, a single electrical lead 19 on the resistor network 18, and respective, fifteen electrical leads 20. Thirteen of the electrical leads 20 are connected by respective circuit paths 21, Fig. 1, to

respective plating lined holes 22 through the circuit board 8. Fig. 1 also illustrates two circuit paths 23 that are unused, whereby, two resistors within the resistor network 18 are unused when they are connected by the respective leads 20 to the respective circuit paths 23.

With reference to Fig. 6, fourteen multiple resistors R1-R14 are bussed, or connected, to a single electrical circuit pad or path 24. With reference to Fig. 2, the pad 24 is on the conductive circuit path 17 referenced to the voltage V-out. The circuit path 17 is near the periphery of the circuit board 8, and substantially circumscribes the periphery of the circuit board 8. A second resistor network 18, Fig. 2, comprises a package containing the multiple resistors R1-R14, and is identical in construction to the first resistor network 18. The resistors within the second resistor network 18 each are connected between, a single electrical lead 19 on the second resistor network 18, and respective, fifteen electrical leads 20. Fourteen of the electrical leads 20 are connected by respective circuit paths 21, to respective, plating lines holes 22 through the circuit board 8. Fig. 1 also illustrates one circuit path 23 that is unused, whereby, one resistor within the second resistor network 18 is unused when it is connected by the respective lead 20 to the circuit path 23. The multiple resistors of the resistor networks 18, 18 comprise a voltage divider circuit coupled between V-out of the voltage regulator 2 and ground.

With reference to Fig. 2, on the voltage regulator 2, the electrical leads 4, 6 are connected together by the manufacturer. The leads 4, 6 are connected to the circuit path 17 that is referenced to the voltage V-out of the voltage regulator 2. With reference to Figs. 2 and 6, a noise reducing capacitor C3, 25 is connected

between V-out on the circuit path 17 and ground on the circuit path 11. With reference to Fig. 1, conductive pads, or paths, 26, 27 are on respective circuit paths 17, 11. The capacitor C3, 25 is connected to the pads 26, 27.

On the schematic view of Fig 6, a noise reducing capacitor C2, 28 is connected between the voltage V-out and ground. With reference to Fig. 2, the capacitor C2 is divided into two capacitors 28a, 28b it being understood that the two capacitors 28a, 28b, combined, have the same electrical capacitance as the single capacitor C2, 28. Both capacitors 28a, 28b are connected between the circuit paths 17, 11.

With reference to Figs. 1 and 2, because the circuit path 17 circumscribes the circuit board 8, it also circumscribes the remaining circuits and the components. The circuit path 17 provides a lengthy circuit path referenced at the voltage V-out. The circuit path 11, referenced to ground, extends along the circuit board 8 to extend toward opposite sides of the circuit path 17. The two capacitors, 28a, 28b, are connected to the ground circuit path 11. The two capacitors 8a, 28b are connected between ground potential and the opposite sides of the circuit path 17. A noise reduction circuit is constructed with the circuit path 17 circumscribing the remainder of the circuit paths on the circuit board 8. The path length of the circuit path 17 is apportioned to extend equally between the pair of spaced apart capacitors. The two capacitors 28a, 28b thereby are equally spaced along the circuit path 17 to distribute their noise reduction function along the circuit path 17. The noise reduction efficiency is increased as compared with using only the single capacitor C2, 28, as suggested by the schematic view of Fig. 6.

For example, capacitor C3 is commercially available as part number 293D226X0010C2T, from Sprague Technologies, Inc. Stamford, Connecticut, rated at 22 microFarads, at V-out. Each of the two capacitors C2, C2, 28a, 28b, is commercially available as part number 12065C104MAT, from AVX Corporation, Myrtle Beach, South Carolina, rated at 50 Volts DC, at V-out.

What has been described is a line terminator 1 comprising a voltage regulator circuit providing a voltage V-out, and a voltage divider circuit comprising the resistor networks 18, 18, and a noise reduction circuit to reduce noise on the lines, for example, the noise reduction circuit comprising the capacitor Cl on the input, term power line, and the capacitors C2 and C3 on the output voltage line V-out. The Capacitor C2 has a lower voltage rating to reduce noise from lower voltage spikes being induced on the output voltage line, V-out. The capacitor C3 has a higher voltage rating to reduce noise from higher voltage spikes being induced on the output voltage line, V-out.

Fig. 7 discloses an alternative voltage regulator that is commercially available, as part number MC34268D, from Motorola Semiconductor Products, Phoenix Arizona. This regulator has eight electric leads 29, with four leads 29 on one side of the regulator connected to the circuit path 17, and with one lead 29 connected to the circuit path 7, and with one lead 29 connected to the circuit path 14. The circuit paths 17, 7 and 14 are identical in both Figs. 1 and 7. Figs. 3 and 4 disclose an electrical connector 30 for connection to a flat cable, not shown, comprising, an insulating housing 31 and four rows of conducting electrical contacts 32. The contacts 32 are constructed with projecting pins 33 arranged in four rows of pins, for plugging into respective plated through holes 13, 15, 22 that are also arranged in four rows of plated

through holes. Opposite ends of the contacts 32 are insulation displacement contacts 34 for connection, in a manner disclosed in U.S. Patent 5,122,079, to respective conductors of a flexible, flat electrical cable, not shown.

Fig. 5 discloses a conductive shield 35 on the bottom surface of the circuit board 8 provided with a conductive grid of a cross-hatched pattern of .010 inches wide traces separated by .010 inches spaces. The grid is referenced to ground, and provides electrical shielding and substantial noise reduction. The grid is preferred over a solid shield, since the mass of the conductive shield will inhibit heat transfer that is necessary for attaining solder flow during solder connection of the circuit components 2, 10, 18, 25, 28a, 28b and the pins 33 of the connector 30 to the conductive circuit paths on the circuit board 8 and the plating lined holes 13,15,22 through the circuit board 8. The shield 35 on the bottom surface of the circuit board 8 augments the shielding effect of the circumscribing circuit path 17 on the opposite side of the circuit board 8, whereby both sides of the circuit board 8 provides for shielding of the circuit comprising the terminator l from unwanted emanations of electrical energy. The two noise reduction capacitors 28a, 28b efficiently distribute active noise reduction over the length of the circuit path 17.