US3528039A - Circuit for adding constant dc bias,supplied by a reference zener diode,to a variable input signal - Google Patents

Description

Sept. 8, 1970 R. H. PARKER 3,528,039

REFERENCE CIRCUIT FOR ADDING CONSTANT DC BIAS SUPPLIED BY A ZENE'R DIODE, TO A VARIABLE INPUT SIGNAL Filed March 22, 1965 i VARIATION 01 0| (D O OI O FIG 3 I5 2 2.5 5 5.5 4 4.5 5 5.5 e 6.5 "I

I INVEVTOR RATIO OF 1 TO I| (-fim) ROBERT H. PARKER ATTORNEYS United States Patent Ofice Patented Sept. 8., 1970 3,528,039 CIRCUIT FOR ADDING CONSTANT DC BIAS, SUP- PLIED BY A REFERENCE ZENER DIODE, TO A VARIABLE INPUT SIGNAL Robert H. Parker, Cedar Rapids, Iowa, assignor to Collins Radio Company, Cedar Rapids, Iowa, :1 corporation of Iowa Filed Mar. 22, 1965, Ser. No. 441,550 Int. Cl. H03g 11/00; G011 17/02 US. Cl. 333--14 8 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a circuit for compressing or expanding the percentage of variation or tolerance of voltage between nodes of a circuit.

It is frequently desired to increase or lower the percentage of variation of the voltage of an AC or DC circuit. This may be desirable in order to permit a more accurate measurement of the voltage variation or else to enable the use of less expensive circuit components as measuring equipment. This invention accomplishes both of these advantages by adding a known regulated signal to the varying output signal to thereby lessen the efiect of the variation of the monitored signal.

It is therefore an object of this invention to provide a circuit by which the tolerance of an output signal can be compressed or expanded.

It is another object of this invention to provide such a circuit in which the tolerance variation can be increased or decreased at will.

It is another object of this invention to provide such a circuit which is useful with both AC and DC circuits.

Further objects, features, and advantages of the invention will become apparent from the following description and claims when read in view of the accompanying drawings wherein like numbers indicate like parts and in which:

FIG. 1 shows a tolerance compressor circuit which is useful with DC,

FIG. 2 shows a compressor circuit which is useful with AC,

FIG. 3 shows a graph of percent of variation versus added signal in terms of the varying signal.

Referring now to the drawing, FIG. 1 shows four resistors 10, '11, 12, and 13 connected in series. Connected between the junction of resistors 10 and 11 and ground is Zener diode 15. A monitoring means 16 is connected between the junction of resistors 11 and 12 and ground, and a voltage dividing resistor 14 is connected between the junction of resistors 12 and 13- and ground. If the variation in voltage at the input V is desired to be compressed or expanded the variation of current 1 must also be so compressed or expanded since by proper selection of component values the variation of I can be essentially equal to the variation of V The effect of the variation of V and consequently I can be changed by adding a known regulated signal 1 to I The addition of a positive signal, with respect to 1 causes a compression of tolerance; while the addition of a negative signal increases or expands the tolerance. With Zener diode 15 poled as shown in FIG. 1 a positive current I is added to I by reversing the polarity of the Zener 15 a negative current 1 is added to 1 The effect of the addition of a regulated current, I on the variation of current I can be demonstrated by considering the current I passing through monitor 16. For example, in FIG. 1 the current passing through monitor 16 is I =I -+I i0.25 I (1) Equation -1 shows an assumed 25% variation of 1 for purposes of illustration; however, any percentage of variation can be compressed or expanded. The 25 variation is decreased by substituting for current 1 a multiple (A) of current 1 Equation 1 then becomes In this manner the variation seen by monitor 16 becomes a 10.25 1 variation over a nominal current of I +AI which gives a variation of [0..215ifj1100] (3) Assuming that it is desired to compress the 25% variation to a 12.5% variation this can be done by regulating current I such that I :I (i.e. A=1) Substituting this value into Equation 1, the equation then becomes I =2I iO.2-5 1 which in accordance with Equation 3 becomes This is a current variation of 10.25 on a nominal current of two which gives a current variation of 12.5% as desired. By changing the relationship of I and 1 any percentage of variation can be obtained. This is shown in Table 1 where A represents the ratio of I to 1 Table I.-I positive A: 1 percent variation seen by monitor 16 0 25.0

As shown in the table, by allowing the coefficient A to vary from 0.25, which gives a percent variation of p to a value of 7, the percent variation can be decreased to i3.l3%. It is obvious that the percent variation can be decreased further simply by increasing the relationship of 1 to 1 In order to expand the tolerance it is necessary to reverse the polarity of Zener diode 15 and reference voltage VDC as shown in FIG. 1. By doing this the current I is negative with respect to the current I The effect of this is to decrease the value of current as shown in Equation 1. For this reason when the ratio to 1 of I is between zero and one (0 A l) the percent of variation changes from a theoretical infinite at the value of A-=1 to i 25 at the value of A'=0. For values of 1 A 2 tolerance expansion is also accomplished but a reversal of monitor 16 polarity is required. For A 2 tolerance compression with monitor 16 polarity reversal occurs. This is shown in Table 2.

Table II.-I negative A: i% variation seen by monitor 16 Referring now to FIG. 3, the solid curve 22 shows the percent variation versus the Al current relationship for positive values of I and broken curve 23 is a similar curve for values when I is negative with respect to I FIG. 2 shows the circuit of FIG. 1 wherein the circuit is adapted for use with AC inputs. In order to accomplish this, diode 20, resistor 17 and capacitor 18 are added to the regulated end of the circuit and diode 21 and capacitor 19 are added to the monitor end of the circuit. Diode 20 is added to rectify the AC signal assuring that only positive values of current are presented to resistor 17 and capacitor 18 which smooths the input current. Diode 21 and capacitor 19 perform a similar function on the monitor end. The operation of the circuit is now the same as that of the FIG. 1 circuit. The circuit as shown in FIG. 2 is useful in compressing the variation of voltage V In order to adapt the circuit for expanding the V tolerance it is necessary to reverse the polarity of Zener diode and diode In the above description both the input current I and current to be monitored I have been either AC or DC. For example, in FIG. 1 both currents are DC while in FIG. 2 both are AC. The similarity of current forms is not essential to the operation of the invention. FIG. 1 can be modified to add an AC input current I to a DC monitored current I by adding diode 20, capacitor 17 and resistor 18 t0 the input end of the circuit in the same manner as shown in FIG. 2. Alternatively, FIG. 1 can be modified to add a DC input current I to an AC monitored current I by adding capacitor 19 and diode 21 to the monitored end of the circuit in the same manner as shown in FIG. 2. It is now evident that four combinations are possible.

(1) DC input with DC monitored (2) AC input with AC monitored (3) DC input with AC monitored (4) AC input with DC monitored Although this invention has been described with respect to particular embodiments thereof, it is not to be so limited, as changes and modifications may be made therein which are within the spirit and scope of the invention as defined by the appended claims.

I claim:

1. A monitoring circuit capable of compressing or ex pandin g variations in a monitored signal comprising monitoring means having first and second terminals, first conductive means connected to said first and second terminals for receiving an input signal and supplying a first current to said monitoring means, second conductive means connected to said first and second terminals for receiving a reference voltage and supplying a regulated second current to said monitoring means, said first conductive means comprising a voltage divider means, and said second conductive means comprising a T configuration voltage divider means including a shunt connected Zener diode for regulating the second current through said monitoring means.

2. A monitoring circuit as defined by claim 1 wherein said reference voltage is a DC voltage, and the polarities of said DC voltage and said Zener diode are arranged so that said first and second currents are cumulative in said monitoring means thereby compressing variations in said monitored signal.

3. A monitoring circuit as defined by claim 1 wherein said reference voltage is a DC voltage, and the polarities of said DC voltage and said Zener diode are arranged so that said first and second currents are opposing in said monitoring means thereby expanding variations in said monitored signal.

4. A monitoring circuit as defined by claim 1 wherein said second conductive means further includes a series connected diode and a shunt connected resistor-capacitor parallel combination for receiving said reference voltage, said reference voltage being AC.

5. A monitoring circuit as defined by claim 4 wherein the polarities of said shunt diode and said series diode are arranged so that said first and second currents are cumulative in said monitoring means thereby compressing variations in said monitored circuit.

6. A monitoring circuit as defined by claim 4 wherein the polarities of said shunt diode and said series diode are arranged so that said first and second currents are opposing in said monitoring means thereby expanding variations in said monitored circuit.

7. A monitoring circuit as defined by claim 1 wherein said first conductive means includes a series connected diode and a shunt capacitor for receiving said input signal, said input signal being AC.

8. A monitoring circuit as defined by claim 4 wherein said first conductive means includes a series connected diode and a shunt capacitor for receiving said input signal, said input signal being AC.

References Cited UNITED STATES PATENTS 2,533,769 12/1950 Couillard 324-131 2,874,354 2/1959' Bell 324-431 OTHER REFERENCES The Zener Diode, Shaughnessy; Popular Electronics, June 1961, pp. 76-82.

ELI LIEBERMAN, Primary Examiner M. NUSSBAUM, Assistant Examiner U.S. Cl. X.R. 324-98

Images