Page 1 of 14
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`(cid:44)(cid:49)(cid:55)(cid:40)(cid:47) EXHIBIT 10(cid:24)(cid:27)
`
`

`

`US. Patent
`
`Sep.15
`
`3
`
`1992
`
`Sheet],of9
`
`5,148,133
`
`
`
`.385
`
`meson
`
`Page 2 of 14
`Page 2 of 14
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`

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`US. Patent
`
`Sep. 15, 1992
`
`Sheet 2 of 9
`
`5,148,133
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`
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`Page 3 of 14
`Page 3 of 14
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`

`

`US. Patent
`
`Sep. 15, 1992
`
`Sheet 3 of 9
`
`5,148,133
`
`
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`Page 4 of 14
`Page 4 of 14
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`

`

`US. Patent
`
`Sep. 15, 1992
`
`Sheet 4 of 9
`
`5,148,133
`
`
`
`Page 5 of 14
`Page 5 of 14
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`

`

`US. Patent
`
`Sep. 15, 1992
`
`Sheet 5 of 9
`
`5,148,133
`
`
`
`
`
`22%
`
`325m
`
`Page 6 of 14
`Page 6 of 14
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`

`

`US. Patent
`
`Sep. 15, 1992
`
`Sheet 6 of 9
`
`5,148,133
`
`
`
`Page 7 of 14
`Page 7 of 14
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`

`

`US. Patent
`
`Sep. 15, 1992
`
`Sheet 7 of 9
`
`5,148,133
`
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`Page 8 of 14
`Page 8 of 14
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`

`

`US. Patent
`
`Sep. 15, 1992
`
`Sheet 8 of 9
`
`5,148,133
`
`NIE00.9Z<n_m,
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`Page 9 of 14
`Page 9 of 14
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`

`

`US. Patent
`
`Sep. 15, 1992
`
`Sheet 9 of 9
`
`5,148,133
`
`52moan.mAil”.
`
`Page 10 of 14
`Page 10 of 14
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`

`

`1
`
`5,148,133
`
`2
`diameter wire. In decoding and descrambling applica-
`tions, however, the Q cannot be improved by utilizing
`larger coils due to the above-described size and corre-
`sponding layout restrictions.
`In view of the above, it is an object of the invention
`to provide a highly reliable, narrow and stable notch
`filter having a high Q while minimizing the overall size
`of the notch filter. Further objects, features and advan-
`tages of the invention will become apparent from the
`ensuing detailed description of the preferred embodi-
`ment of the invention taken in connection with the
`accompanying drawings
`SUMMARY OF THE INVENTION
`
`QUALITY FACTOR IMPROVEMENT FOR FILTER
`APPLICATIONS
`
`FIELD OF THE INVENTION
`
`The invention relates in general to tuned filters. More
`specifically, the invention relates to tuned filters, such
`as notch filters, which are particularly well suited for
`use in removing single or multiple frequency scram-
`bling signals injected into a communication signal to
`eliminate the possibility of intelligible reception of
`video and/or audio information, or for use in removing
`a video carrier in a television channel to prevent its
`reception.
`BACKGROUND OF THE INVENTION
`
`5
`
`10
`
`l5
`
`The present invention is based on the recognition that
`the Q of a tuned filter can be improved, while minimiz-
`ing the overall size of the filter to within restricted
`cavity size limitations, by replacing single inductors and
`capacitors in conventional filter structures with parallel
`multiple inductors and/or multiple series capacitors as
`required.
`More specifically, in a preferred embodiment of the
`invention, a tuned filter is provided that includes an
`input terminal and an output terminal; a first network
`coupled to the input terminal and electrical ground
`including a plurality of series capacitors and/or a plu-
`rality of parallel inductors; and a second network cou-
`pled to the input terminal and the output terminal in-.
`cluding at least one of a plurality of series capacitors
`and/or a plurality of parallel inductors. The Q of the
`filter is improved by the use of the series capacitors
`and/or parallel inductors opposed to single capacitors
`or inductors.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`It has long been a customary practice for subscription
`television communication systems—a system in which
`the reception of a television program signal, generally
`recoverable by a group of television receivers, is limited 20
`to specifically authorized receivers—to scramble or
`encode their television transmission signals to prevent
`unauthorized reception by individuals who have not
`paid a subscription fee. Conventional hard-wired com—
`munity antenna television systems (CATV), for exam- 25
`ple, are representative of a typical subscription televi-
`sion communication system, although other systems
`have been developed that employ radio frequency (RF)
`transmission to subscribers instead of hard-wiring. If the
`subscription television system provides more than one 30
`channel, it is also desirable to provide selected scram-
`bling or securing of individual channels that are used to
`provide premium services.
`One of the methods most commonly employed to
`prevent unauthorized reception to add a scrambling 35
`signal or interfering carrier signal
`to the television
`transmission signal between its aural and visual carriers.
`The scrambling signal is added to the television trans-
`mission signal to provide additional information which
`causes a television receiver to reconstitute the scram- 40
`bled television transmission signal
`in an incoherent
`form. The scrambling signal is removed by passing the
`scrambled television transmission signal
`through a
`tuned notch filter at the site of an authorized television
`receiver.
`Tuned notch filters to be utilized in the video/audio
`frequency removal or descrambling process must meet
`several critical requirements. For example, it is critical
`that the tuned notch filter have a high degree of stability
`and reliability. In addition, the size of the notch filter SO
`must remain small, preferably less than 0.825 inch diam-
`eter, to enable the notch filter to be utilized in typical
`installations where one or more filters are mounted on a
`directional tap on a strand, in a pedestal, or some other
`Referring first to FIG. 5, an electrical schematic
`small enclosure. The notch filter must also be capable of 55
`diagram of a conventional notch filter of the general
`a large degree of attenuation at the center frequency of
`type described in US. Pat. No. 4,451,803 is shown. An
`the notch with very sharp skirts and a narrow band-
`input terminal 8 is provided to receive an incoming
`width to minimize unwanted attenuation of adjacent
`communication signal, such as a television signal, in-
`channels. As the frequency requirements increase,
`cluding one or more signals which are to be removed
`sharper skirts are required to maintain the desired band— 60
`(attenuated) by the notch filter. Input terminal 8 is con-
`width while minimizing interference with adjacent
`channels.
`,
`nected to one terminal of capacitor C5 and the other
`terminal of capacitor C5 is connected to one terminal of
`In order to achieve sharper skirts, the notch filter
`’ a parallel arrangement of a capacitor C2 and an induc-
`must have a high Q (Quality Factor), i.e., the bandwidth
`tor L2. The other terminal of the parallel arrangement
`is minimized by optimization of the Q of the notch 65
`of capacitor C2 and inductor L2 is connected to a
`filters’ inductors and capacitors. In most applications,
`the Q of the notch filter can be improved by utilizing
`ground conductor. Terminal 8 is also connected to one
`terminal of an inductor L8 in parallel with a network
`inductors having larger winding diameters with larger
`
`With the above as background, reference should now
`be made to the detailed description of the preferred
`embodiment of the invention and the accompanying
`drawings in which:
`FIGS. la—le are an electrical schematic diagrams of
`filters in accordance with the invention;
`FIG. 2 is a top plan view of a notch filter constructed
`on a Circuit board in accordance with the invention;
`FIG. 3 is a sectional side view through a notch filter
`of the type illustrated in FIG. 2 and accompanying
`housing;
`FIG. 4 is a data plot of a notch filter in accordance
`with the present invention overlaid on a data plot of a
`conventional notch filter; and
`FIG. 5 is a schematic of a conventional notch filter.
`
`45
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`
`Page 11 of 14
`Page 11 of 14
`
`

`

`5,148,133
`
`4
`
`RLO+XLO=0.03409+j16.l5
`
`Qo=XLO/RLO= l6.15/0.03409=473.7
`
`Lo=Xm/jw= 16.15/21'f= 0.0257 pH
`
`10
`
`I5
`
`20
`
`25
`
`30
`
`35
`
`4O
`
`45
`
`50
`
`55
`
`65
`
`the resulting inductance of the two coils
`Thus,
`(0.0257 pH) is the same as the inductance of the single
`coil (0.0258 pH) if the round—off errors are taken into
`account. The Q of the two coils (473.7) is significantly
`improved, however, over the Q of the single coil
`(337.3).
`
`Case2
`
`Two unequal coils to equal one coil of less inductance
`if the desired inductance is La=0.0435 pH and f: 100
`MHz.
`The desired inductance can be achieved with one
`0.180" diameter coil having 2.5 turns using 26 Gauge
`wire. The calculated theoretical value for this coil is
`Lo=0.0435 pH with Qa=333.l@100 MHz.
`Arbitrarily picking one coil to be a 7.5 turn, 0.180”
`diameter coil using 26 Gauge wire, the other coil needs
`to be a 5.5 turn, 0.096" diameter coil using 24 Gauge
`wire. The resulting inductance and Q, for these coils, is
`as follows:
`
`Ll =0.2264 air with Q1= 577.4@100 MHZ
`
`L2=0.0539 pH with Q2=399.7@100 MHZ
`Calculating the resistances, impedances, and resultant
`inductance and Q, as in Case I, give the following re-
`sults:
`
`Lo=0.0436 p.” with 90:424.9@100 MHZ
`The resulting inductance of the two coils (0.0436 pH) is
`the same as the inductance of the single coil (0.435 pH)
`if the round-off errors are taken into account. The Q of
`the two coils (424.9) is significantly improved over the
`Q of the single coil (333.1).
`Case3
`
`Two capacitors to equal one capacitor of less capaci-
`tance.
`
`Using a similar analysis to Case 1 and Case 2, an
`improvement, in Q, can be shown for two capacitors
`used in a series configuration where Co: 1.0 pF is the
`desired capacitance and f= 100 MHz.
`The desired capacitance can be achieved with one 1.0
`pF capacitor which has a Q of 2420._The single capaci-
`tor can be replaced by two 2.0 pF capacitors in series
`which have a resultant capacitance of 1.0 pF and a
`resultant Q of 2440, or by g 1.5 pF capacitor in series
`with a 3.0 pF capacitor which have a resultant capaci—
`tance of 1.0 pF and a resultant Q of £439.56. In both
`examples, the resultant capacitance was 1.0 pF, as de-
`sired, and an improvement in Q from 420 to approxi-
`mately 440 was shown over a single capacitor of the
`same capacitance.
`,
`Referring now to FIG. 1a, an electrical schematic
`diagram of a notch filter in accordance with the inven-
`tion is illustrated. A prime notation (’) will be used to
`indicate components which correspond to the compo:
`nents of the conventional notch filter illustrated in FIG.
`5. The notch filter shown in FIG. 1 includes an input
`terminal 8' that is coupled to a television signal source
`to receive an input signal. The input terminal 8’ is con-
`nected to one terminal of a network including multiple
`
`3
`consisting of capacitor C1 in series with an inductor L1.
`The other terminal of the network passes into an isola-
`tion area 4 and is connected to one terminal of a cou-
`pling capacitor C9. The circuitry described thus far,
`prior to the coupling capacitor C9, forms one filtering
`section 15.
`The other terminal of capacitor C9 connects into
`filtering section 14 of the notch filter to one terminal of
`an inductor L11 which is connected in parallel with a
`network consisting of inductor L4 in series with a ca-
`pacitor C4. The other terminal of this network is con-
`. nected to the output terminal 9. Output terminal 9 is
`also connected to one terminal of capacitor C8 which in
`turn is connected at its other terminal to a parallel ar-
`rangement of a capacitor C3 and inductor L3. Remain-
`ing television signals exit through terminal 9.
`The invention is based on the recognition that two or
`more inductors of the proper values can be connected in
`parallel to obtain a desired inductance with a Q that is
`greater than the Q for a single inductor of the equivalent
`inductance, and/or two or more capacitors of the
`proper values can be connected in series to obtain a
`desired capacitance with a Q which is greater than the
`Q for a single capacitor of equivalent capacitance in
`several areas of the conventional notch filter illustrated
`in FIG. 5. Having discovered this advantageous effect,
`our subsequent mathematical analyses confirmed that
`the utilization of two or more inductors or capacitors to
`replace a single inductor or capacitor can improve the
`Q of the overall notch filter:
`Case 1
`
`Two equal coils to equal one coil of half inductance
`where I.o=0.0258 pH is the desired inductance and
`f= 100 MHz.
`The desired inductance can be achieved with one
`0.125” diameter coil having 2.5 turns using 24 Gauge
`wire. The calculated theoretical value for this coil is
`Lo=0.0258 pH with Qo=337.8@100 MHz.
`Knowing that two coils in parallel add per the fol-
`lowing:
`
`Lo=(Li‘1+Lz")“
`
`For two equal coils, it can be determined that:
`
`L1=L2=0.05l4 {it}!
`
`This desired inductance for two equal coils can‘be
`achieved with 0.119" diameter coils having 4.5 turns
`using 22 Gauge wire. The calculated theoretical value
`for these coils is:
`
`L1=L2=0.0514 nu with 91:92:473.7@100 MHZ
`XL} =XL2=jWL1=j2TfL1 =j32.3@100 MHZ
`
`RL1=RL2=XL1/Q]=32.3/473.7=0.0682 (I
`
`Since;
`
`ZL=RL+XL
`
`and;
`
`ZLo=(ZL1“+ZL2‘ 1)‘1
`then
`
`RLo+Xm=((RLI+XL1)‘1+(RL2+XL2)"l"
`
`Page 12 of 14
`Page 12 of 14
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`

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`5,148,133
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`5
`
`10
`
`15
`
`20
`
`25
`
`,
`5
`capacitors C15 and C6 which are connected in a series
`configuration which gives them an increased Q as con-
`firmed by the calculations provided above. The capaci-
`tor C6 is connected to a parallel arrangement of at ca-
`pacitor C2' and multiple inductors L12 and L9. The
`inductors L12 and L9 are placed in a parallel configurav
`tion to increase the Q as described by the calculations
`provided above. The other terminal of the network
`including capacitor C2’ and inductors L12 and L9 is
`connected to a ground conductor. Terminal 8' is also
`connected to one terminal of a network consisting of
`inductors L7 and L18, arranged in parallel for an im-
`provement in Q, in parallel with a network consisting of
`capacitor C1’ which is in series with multiple inductors
`L11 and L5 arranged in parallel for an improvement in
`Q. The circuit described thus far forms one filtering
`section 15’ of the overall notch filter illustrated in FIG.
`1. The filtering section 15', specifically the network
`including the multiple parallel inductors L18 and L7
`and the network including capacitor C1' in series with
`parallel inductors L11 and L5 is connected to a cou-
`pling capacitor C9’ of an isolation area 4’, An optional
`capacitor C31 coupled between the network and
`ground may also be utilized to improve high frequency
`response.
`The other terminal of capacitor C9' connects into
`filtering section 14’ to one terminal of a network (a
`capacitor C32 may also be provided as shown to im-
`prove high frequency response), consisting of multiple
`inductors L22 and L21, connected in parallel for an
`improvement in Q, which are in parallel with a terminal
`of a network consisting of multiple inductors L14 and
`L6, connected in parallel for an improvement in Q, in
`series with a capacitor C4’. The other terminal of this
`network is connected to the output terminal 9'. Output
`terminal 9’ is also connected to a terminal of a network
`including multiple capacitors C18 and C7 which are
`connected in a series configuration to give them an
`increased Q. Capacitor C7 is connected to a parallel
`arrangement of a capacitor C3’ and inductors L13 and
`L10. The inductors L13 and L10 are arranged in a par-
`allel configuration to increase the Q. The other terminal
`of the parallel arrangement of capacitor C3' and induc-
`tors L13 and L10 is connected to a ground conductor.
`output terminal 9’ and are supplied to a customer drop
`coupled to the output terminal 9’. The customer drop is
`then connected to a television monitor.
`FIG. 1a thus shows two separate filtering sections 15'
`and 14’ which correspond to the filtering sections 15
`and 14 of the conventional notch filter illustrated in
`FIG. 5. The first filtering section 15’ exists between
`input terminal 8' and isolation area 4' and the second
`filtering section 14’ exists between isolation area 4’ and
`output terminal 9’. The components of the filtering
`sections 14’ and 15' and the isolation area 4' are physi-
`cally arranged on a circuit board as shown in FIG. 2.
`The circuit board is placed within a housing as shown in
`FIG. 3.
`In the preferred embodiment of the invention illus-
`trated in FIG. la, the inductors L2, L3, L8, ‘L1, L11 and
`L4 of the conventional notch filter illustrated in FIG. 5
`were replaced by the parallel arrangements of inductors
`(L12, L9), (L13, L10), (L18, L7), (L11, L5), (L21, L22)
`and (L14, L6), respectively, to improve the overall Q of
`the notch filter. Similarly, the capacitors C5 and C8 of 65
`the conventional notch filter were replaced by the series
`capacitors (C15, C6) and (C18, C7), respectively, to
`improve the overall Q of the notch filter.
`
`6
`A further benefit of the invention is the ability to
`adjust or tune L11, L12, L13, and L14 to a natural pitch
`configuration, which in practice improves the Q. Natu—
`ral pitch is the condition where a coil is positioned such
`that the space between adjacent turns is the same as the
`wire diameter. In previous designs of the type illus-
`trated in FIG. 5, the coils were designed for a natural
`pitch condition, but component tolerances sometimes
`made it necessary to compress or stretch the coils from
`a natural pitch condition to compensate for tolerances.
`The coil windings and spaces for the preferred embodi-
`ment of the invention are shown on FIG. 3 as indicated
`by L11, L12, L13, and L14. Since parallel coils exist to
`obtain the desired inductance value, the inductors L11,
`L12, L13, and L14 can be positioned for a natural pitch
`condition and tolerances can be compensated for by
`stretching or compressing L5, L6, L9, and L10.
`FIG. 4 shows the difference in performance of a
`conventional tuned notch filter of the type illustrated in
`FIG. 5 (shown as a dashed line) and a tuned notch filter
`of the type illustrated in FIG. 1 (shown as a solid line).
`The filter illustrated in FIG. 5 has an overall Q of 45.467
`while the filter in FIG. la has an overall Q of 101.05. As
`can be readily appreciated, the notch filter of the inven-
`tion has a much sharper response and corresponding
`40% or greater improvement in bandwidth, characteris-
`tics which are highly desirable when used in higher
`frequency television channels. Thus, conventional fil-
`ters having Q’s ranging from 35—60 can be easily modi-
`fied by the practice of the invention to yield Q’s. of 70
`or greater with corresponding improvements in re-
`sponse.
`The invention has been described with reference to
`certain preferred embodiments thereof. It will be under—
`stood, however, that variations and modifications are
`possible within the scope of the appended claims. For
`example, although the invention was described with
`reference to a notch filter having two filtering sections,
`the invention is applicable to filters having more than
`two filtering sections. For example, one or more of the
`filter or filter sections can be connected in series to
`obtain better frequency response with more attenuation.
`The invention is also applicable to filters in general and
`is not limited solely to notch filters. It will also be un-
`derstood that various permutations of the basic filter
`structure are possible, i.e., series capacitors and/or par-
`allel inductors can be used to replace single elements
`throughout the filter structure in any desired combina-
`tion. Several examples of such permutations are illus-
`trated in FIGS. lb-le.
`What is claimed is:
`1. A filter comprising: an input terminal and an output
`terminal; a first network, including at least two series
`capacitors connected to at least two inductors and at
`least one capacitor arranged in parallel, coupled to the
`input terminal and electrical ground; a second network
`and a third network connected in parallel and coupled
`to the input terminal and the output terminal, wherein
`the second network includes at
`least two inductors
`coupled in parallel and the third network includes at
`least one capacitor connected in series to at least two
`parallel inductors.
`2. The filter as claimed in claim 1, wherein the input
`terminal is coupled to a television signal source and the
`output terminal is coupled to a television monitor.
`3. The filter as claimed in claim 2, further comprising
`a capacitor connected between the output terminal and
`electrical ground.
`
`30
`
`35
`
`45
`
`50
`
`55
`
`Page 13 of 14
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`

`7
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`5,148,133
`
`8
`and electrical ground including at least one capacitor
`connected in series to the combination of at least one
`capacitor coupled in parallel with a plurality of induc-
`tors, a second network coupled to the input terminal
`and the output terminal including at least one inductor
`connected in parallel to the combination of at least one
`capacitor coupled in series with a plurality of parallel
`inductors.
`8. A filter as claimed in claim 7, further comprising a
`third network and a fourth network coupled between
`the second network and the output terminal, wherein
`the third network is connected to an output of the sec-
`ond network and to the output terminal and the fourth
`network is connected to output terminal and electrical
`ground, and wherein the third network includes a single
`inductor or a plurality of parallel inductors connected
`in parallel with a single capacitor or a plurality of series
`capacitors in series with a single inductor or a plurality
`of inductors, and the fourth network includes a single
`capacitor or a plurality of series capacitors connected to
`a single capacitor or a plurality of series capacitors in
`parallel with a single inductor or a plurality of parallel
`inductors.
`9. The filter as claimed in claim 8, further comprising
`a blocking capacitor coupled between the second net-
`work and the third network.
`10. The filter as claimed in claim 7, further compris-
`ing a capacitor coupled between the output of the sec-
`ond network and electrical ground to improve higher
`frequency response.
`_
`11. The filter as claimed in claim 8, further compris-
`ing a capacitor coupled between an input to the third
`network and electrical ground to improve higher fre-
`quency response.
`t
`t
`i
`t
`It
`
`4. A filter comprising:
`an input terminal, an output terminal and an isolation
`section located between the input terminal and the
`output terminal;
`a first filtering section comprising a first network 5
`including at least two series capacitors connected
`to at least two inductors and at least one capacitor
`arranged in parallel, wherein the first network is
`connected to the input
`terminal and electrical
`ground. a second network and a third network 10
`connected in parallel and coupled to the input ter-
`minal and the isolation section, wherein the second
`network includes at least two inductors coupled in
`parallel and the third network includes at least one
`capacitor connected in series to at least two parallel
`inductors; and
`a second filter section comprising a fourth network
`and a fifth network connected in parallel and cou-
`pled to the isolation section and the output termi-
`nal, wherein the fourth network includes at least
`two inductors coupled in parallel and the fifth net-
`work includes at least one capacitor connected in
`series to at least two parallel inductors, and a sixth
`network including at least two series capacitors
`connected to at least two inductors and at least one
`capacitor arranged in parallel, wherein the sixth
`network is coupled to the output terminal and elec-
`trical ground.
`5. The filter as claimed in claim 4, wherein the input
`terminal is coupled to a television signal source and the
`output terminal is coupled to a television monitor.
`6. The filter as claimed in claim 4, wherein the isola-
`tion section includes a capacitor which blocks AC/DC
`currents.
`
`25
`
`30
`
`15
`
`20
`
`7. A filter comprising: an input terminal and an output 35
`terminal, a first network coupled to the input terminal
`
`45
`
`50
`
`55
`
`65
`
`Page 14 of 14
`Page 14 of 14
`
`