Circuit board having printed thereon conductive patterns to be connected with input and output lead wires of acoustic surface wave filter element

An acoustic surface wave filter element provided with two input and two output pins connected with the input and the output interdigital electrodes, respectively and an earth pin connected with a filter element shield casing is disposed on one surface of a circuit board, with the five pins extending through corresponding through holes in the circuit board to the other surface of the circuit board on which the pins are connected with corresponding conductive circuit patterns of the circuit board. The circuit patterns include a first signal pattern to be connected with one of the input pins, a first earth pattern connected with the other of the input pins, a second and a third signal pattern connected with one and another of the output pins, and a second earth pattern connected with the earth pin of the filter element. The first and the second signal pattern have end portions opposedly positioned to each other, and an earth pattern portion is positioned between the opposed end portions of the first and the second signal pattern to connect the first and the second earth pattern with each other. Portions of the patterns positioned beneath the filter element are arrayed symmetrically about an axis lying on the center of the terminal of the end portion of the first signal pattern and external between the second and third signal patterns.

This invention relates to a printed circuit board which has printed thereon 
conductive patterns to be connected with input and output lead wires of an 
acoustic surface wave filter element having a desired frequency 
characteristic, and particularly to a printed circuit board for the video 
intermediate frequency circuit (VIF circuit) in television receiver sets. 
Acoustic surface wave filters (ASF) are well-known and their use in video 
intermediate frequency circuits in television receiver sets has been 
taught in U.S. Pat. No. 3,582,838. The acoustic surface wave filter 
elements are a kind of filter element wherein an electrical signal applied 
to the input lead wires is internally propagated in the form of an 
acoustic oscillation to derive an electrical signal in the output lead 
wires. The acoustic surface wave filter elements are normally mounted, 
together with other circuit elements, on circuit boards to provide certain 
circuit parts. It has, however, been observed in operation of such a 
filter element mounted on a circuit board with the input and the output 
lead wires connected with patterns printed on the board that unnecessary, 
undesirable response signals are derived into the output lead wires 
earlier than the desired output signals derived through propagation in the 
filter element from those applied to the lead wires. 
Such unnecessary response signals cause production of particularly beat 
patterns and ghost images in television receiver sets. 
Accordingly, one of the objects of the invention is to provide a printed 
circuit board which has printed thereon conductive patterns connected with 
the input and the output lead wires of an acoustic surface wave filter 
element having a desired frequency characteristic whereby to minimize the 
influence of such unnecessary response signals derived into the output 
lead wires of the acoustic surface wave filter element. 
Another object of the invention is to provide a printed circuit board for 
video intermediate frequency circuits of television receiver sets, 
avoiding occurrence of ghost images and beat patterns by minimizing the 
influence of an undesired parasitic filter formed between the input and 
output terminals of an acoustic surface wave filter. 
According to the invention, provided is a circuit board including: 
an insulating board having its one surface to be provided with an acoustic 
surface wave filter element and two pairs of through holes formed therein 
to respectively receive paired input and paired output lead wires of the 
filter element; and 
a plurality of conductive patterns formed on the other surface of said 
insulating board to be correspondingly connected with the four lead wires 
extending through the through holes and protruding from the other surface 
of said insulating board; 
the plurality of conductive patterns including a first signal pattern to be 
connected with one of the input lead wires for the application of an input 
signal, a second and a third signal pattern both having first end portions 
to be connected with one and another of the output lead wires and the 
second end portions of the said signal patterns to be connected with the 
input lead wires of a differential amplifier, the first end portions being 
positioned adjacent the first signal pattern, and an earth pattern 
surrounding the first, second and third signal patterns and to be 
connected with the other of the input lead wires of the filter element, 
the patterns being arranged in an array such that voltages inductively 
generated the second and third signal patterns by action of a current 
flowing through the filter element between the first signal and the earth 
pattern are substantially equivalent to each other.

Referring to FIGS. 1A and 1B showing a printed circuit board 2 according to 
one embodiment of the invention, circuit elements such as resistors, 
capacitors, coils, for as b matching, semiconductors, and the like are 
arranged on one surface (not shown) of an insulating board 4 of the 
circuit board 2. On the other surface thereof, a printed pattern 6 is 
formed as shown by the well-known printing technique, and comprises an 
earth pattern 8 and a plurality of signal patterns 10, the latter being 
principally surrounded by the earth pattern 8. The earth pattern 8 and the 
signal patterns 10 have a plurality of through holes 12 formed in 
determined positions thereof to extend through the insulating board 4. 
Said circuit elements arranged on one surface of insulating board 4 have 
the respective lead wires extending through the through holes 12 and the 
distal ends of these lead wires protrude from the other surface of 
insulating board 4. Thus, the protruding distal ends of the lead wires are 
positioned in place and soldered on pads 14 disposed on printed pattern 6 
so that the respective circuit elements are electrically connected with 
the earth pattern 8 and/or the signal patterns of printed pattern 6. Some 
circuit elements that are necessary for description of the circuit board 
are exclusively illustrated by symbols at 16, 18, 20, 22, 24, 25 and 26. 
It should be understood that other than the illustrated elements are in 
fact disposed on the one surface of circuit board and electrically 
connected with the printed circuit patterns, but which elements are 
omitted from the illustration for convenience of explanation. 
Description will hereinafter be made of an acoustic surface wave filter 
element 24 and related circuit elements 16, 18, 20, 22 and 26 mounted on a 
circuit board 2 and to circuit patterns for electrically connecting these 
circuit elements. As shown in FIG. 2, the acoustic surface wave filter 
element 24 usually has five lead wires or lead pins 28, 30, 32, 34 and 36 
of an equal length and is housed in a shield casing 38 for shielding the 
same. Of the five lead wires, two input leads wires 28 and 30 are 
connected with two input interdigital electrodes (not shown) and two 
output lead wires 32 and 34 with two output interdigital electrodes (not 
shown) of filter element 24 and an earth lead wire 36 is connected with 
the shield casing 38. The filter element 24 is mounted on circuit board 2 
positioned on the one surface thereof as shown in dotted line of FIG. 1 
which dotted line shows the contour of the stem or body 40 of filter 
element 24 as in FIG. 2. 
The above stated signal patterns consist of signal patterns 10-1, 10-2, 
10-3, 10-4, 10-5 and 10-6 in a signal pre-amplifier area 42 and signal 
patterns 10-7, 10-8 and 10-9 in a filter area 44, the signal patterns 10-1 
to 10-6 in the signal amplifier area being surrounded by the earth pattern 
8, as shown, to be electrically shielded from signal patterns in any other 
areas. With a pad 14-11 on the first signal pattern 10-1 and pad 14-E1 on 
the earth pattern 8 connected are a pair of lead wires of a connector (not 
shown) for application of signals. The first signal pattern 10-1 further 
has a pad 14-12 connected by a bypass capacitor 16 with a pad 14-21 on the 
second signal pattern 10-2 which is in turn connected at a pad 14-22 
thereof with the base of a transistor 18. The transistor has its emitter 
connected with a pad 14-31 on the third signal pattern 10-3, and its 
collector connected with a pad 14-41 on the fourth signal pattern 10-4. 
The third signal pattern 10-3 connected with the emitter of transistor 18 
is connected through another signal pattern with the earth pattern 8, and 
the fourth signal pattern 10-4 connected with the collector of transistor 
18 is similarly connected with a voltage source (not shown). The fourth 
signal pattern 10-4 further has a pad 14-42 connected with a bypass 
capacitor 20 which is in turn connected with the input signal pattern 10-7 
for the filter element 24 in the filter area 44. Thus, an input signal 
applied in pad 14-11 connected with the connector is fed through bypass 
capacitor 16 to the base of transistor 18 where the input signal is 
amplified, and the amplified signal is derived through bypass capacitor 20 
into the signal pattern 10-7. When the foregoing circuit board is intended 
to form a filter part of video intermediate frequency (hereinafter called 
VIF) circuit, pads 14-11 and 14-E1 being coupled to the signal output 
terminals on a TV tuner. 
With a pad 14-72 on the input signal pattern 10-7 in filter area connected 
is one input lead wire 28 of the acoustic surface wave filter element 24, 
the other input lead wire 30 of which is connected with a pad 14-E2 on the 
earth pattern 8. The earth lead wire 36 connected with the shield casing 
38 of filter element 24 is connected with a pad 14-E3 on the earth pattern 
8. 
Besides the first output signal pattern 10-8, a second output signal 
pattern 10-9 is formed on the insulating board 4. These output signal 
patterns 10-8 and 10-9 extend substantially parallel to each other. They 
have one end positioned near one end of the input signal pattern 10-7, 
i.e., the pad 14-72. The output signal patterns 10-8 and 10-9 are each 
provided at one end with pads 14-81 and 14-91, respectively. Pads 14-81 
and 14-91 are connected to the output lead wires 32 and 34 of the filter 
element 24, respectively. Further, the output signal patterns 10-8 and 
10-9 are provided at the other end with pads 14-82 and 14-92, 
respectively. Pads 14-82 and 14-92 are connected to both input terminals 
of the differential amplifier 26 which are not maintained at earth 
potential. The output of the differential amplifier 26 is coupled to a 
circuit not shown. 
As a result of the above-described circuit arrangement, a response 
generated by the stray capacitance or stray inductance between the input 
and output terminals of an ASF, i.e., between the pads 14-72 and 14-81 and 
between the pads 14-72 and 14-91 is reduced. This means that the influence 
of a parasitic filter, which is formed when an ASF is provided on a 
circuit board, is eliminated. The undesired response between pads 14-72 
and 14-81 and the undesired response between pads 14-82 and 14-92 which 
could not be suppressed are made equal and then applied to the input 
terminals of differential amplifier 26 (i.e., pads 14-82 and 14-92). Thus, 
these unnecessary responses are cancelled. 
Before describing individual embodiments of this invention, it will be 
explained why undesired response signals, typically undesired responses 
between the input and output terminals of an ASF, are generated. 
The unnecessary response signals are assumed to be derived not from the 
acoustic oscillation propagated in an acoustic surface wave filter 
element, but from voltages generated in the output signal patterns 10-8 
and 10-9 by direct induction between the input and the output patterns 
connected with the input and output lead wires. Such direct induction 
would take place because of stray capacitance and mutual inductance 
present between the input and the output patterns and resonance current 
flowing from the input signal pattern to the earth pattern. Specifically, 
the unnecessary response signals result from direct induction caused by 
the stray capacitance because a resonance current signal is transmitted 
through the stray capacitance between the input and output of the filter 
element 24 to the output signal patterns 10-8 and 10-9, thereby inducing 
an undesired response in the output signal pattens 10-8 and 10-9. The 
undesired response signals results also from direct induction caused by 
the mutual inductance because the resonance current flows to the mutal 
inductance through a resonance current path or between the input signal 
pattern 10-7 and the earth pattern, thereby electromagnetically inducing 
the undesired response in the output signal patterns 10-8 and 10-9. 
Direct induction by the stray capacitance and mutual inductance will be 
described by reference to FIGS. 3A and 3B. The acoustic surface wave 
filter element is diagrammatically shown in FIG. 3A in the form of an 
equivalent circuit generally called "closed field model". There are in the 
input side of the filter element resistance 46 generated by the 
electromechanical conversion, resistance 50 across the input interdigital 
electrode, and capacitance 54 generally called clamp capacitance across 
the input interdigital electrode, and similarly in the output side of the 
filter element resistances 48 and 52, and capacitance 56. The clamp 
capacitance 54 has a great influence as an insertion loss as the acoustic 
surface wave filter element 24 has been coupled in a circuit. To lower the 
insertion loss by the clamp capacitance 54, an inductance 22 tuned with 
the clamp capacitance 54 is, as shown in FIGS. 1 and 3, connected between 
pads 14-71 and 14-E4 on the signal pattern 10-7 and the earth pattern 8. 
Additionally speaking, it has been known in the U.S. Pat. No. 3,582,838 
that such an inductance as 22 is connected in the input side of the 
acoustic surface wave filter. The inductance 22 and the clamp capacitance 
54 are connected in parallel with each other between the signal pattern 10 
and the earth pattern 8, so that upon application of a signal 
therebetween, a resonance current is caused to flow in the earth pattern 8 
which results in generation of the unnecessary response signal in output 
signal patterns 10-8 and 10-9. Another inductance 25 is connected between 
pads 14-83 and 14-93 on output signal patterns 10-8 and 10-9 for the 
similar purpose to that of connection of inductance 22. 
FIG. 3B shows an equivalent circuit which is a combination of the 
equivalent circuit of the "closed field model" shown in FIG. 3A, and 
further includes the representation of stray capacitance 53 and mutual 
inductance 55. As FIG. 3B illustrates, when a resonance current signal 
flows between clamp capacitance 54 and inductance 22, the signal is 
transferred to the first signal output pattern 10-5 and the second signal 
output pattern 10-9 through stray capacitance 53 and mutual inductance 55. 
As a result, an undesired response signal is generated in each signal 
output pattern. 
If an ASF is used, it is necessary to suppress not only a main signal which 
propagates in the ASF at the acoustic wave propagation speed but also a 
signal which is induced directly by the above-mentioned undesired response 
and which propagates through the space between the input and output 
terminals of the ASF at the electromagnetic wave propagation speed. 
For example, if the filter of the VIF stage of a television receiver set 
includes an ASF, an undesired response signal is generated by the stray 
capacitance of stray inductance between the input and output terminals of 
the ASF and propagates through the space between the input and output 
terminals of the ASF. This undesired response signal will appear in a 
reproduced image, causing a ghost phenomenon. The undesired response 
generated by stray capacitance or stray inductance would degrade the 
frequency characteristic of the ASF. This makes it impossible to obtain a 
sufficient frequency characteristic for the VIF state of the television 
receiver set. As a result, a reproduced image will be deteriorated. 
For the reasons mentioned above, it is necessary to minimize the absolute 
values of an undesired response generated by stray capacitance or stray 
inductance between the input and output terminals of an ASF, if provided 
on a printed circuit board. 
It should be understood that because the output signal patterns 10-8 and 
10-9 are arranged independently from each other on insulating board 4 and 
are both connected with the differential amplifier 26, without being 
connected with the earth pattern 6, that unnecessary response signals, if 
present at an equal voltage in both patterns 10-8 and 10-9, are to be 
cancelled by means of the differential amplifier 26. Signals intended to 
be derived can be amplified in the differential amplifier 26 for 
application from its output to the subsequent stage, since their phases 
are in a reversed relationship to each other in the output signal 
patterns. 
Means for decreasing and equalizing levels of unnecessary response signals 
in the output signal patterns are provided in the following manner. 
Referring to FIGS. 1A and 1B, the pad 14-E2 on earth pattern 8 at which one 
30 of the input lead wires of acoustic surface wave filter element 24 is 
connected by an earth pattern portion 8-1 with the pad 14-E3 on earth 
pattern 8 at which the earth lead wire 36 connected with the shield casing 
38 of filter element 24 is connected therewith. It is preferred that the 
earth pattern portion 8-1 be narrowed as much as possible. 
The conductor means between the pads 14-E3 and 14-E2, i.e., the earth 
pattern portion 8-1, reduces an undesired response generated by stray 
capacitance or stray inductance between the input and output terminals of 
an ASF, in the following manner. 
The stray capacitance between the input and output terminals of an ASF, 
i.e., between the pads 14-72 and 14-81 and between the pads 14-72 and 
14-91, transfers an electromotive force from the input pattern 10-7 to the 
first output pattern 10-8 and the second output pattern 10-9. The earth 
pattern portion 8-1 shields this electromotive force and thus reduces the 
same very much, thereby minimizing the undesired response generated by the 
stray capacitance between the input and output terminals of the ASF. 
Now it will be described how to cancel the undesired response generated by 
stray inductance between the input and output terminals of the ASF. 
As disclosed in U.S. Pat. No. 3,582,838, an inductance 22 is connected to 
the input of the ASF to achieve ASF matching. The inductance 22 resonates 
with a stray capacitance 54 existing in the ASF element. The resonance 
current flows in a loop constituted by the input signal pattern 10-7, the 
pad 14-72, the capacitance 54, the pad 14-E3, the earth pattern 8, the pad 
14-E4, the inductance 22, the input signal pattern 10-7 and the pad 14-72 
and another loop constituted by the input signal pattern 10-7, the pad 
14-72, the capacitance 54, the pad 14-E2, the earth pattern 8, the pad 
14-E4, the inductance 22, the input signal pattern 10-7 and the pad 14-72. 
As shown in FIG. 3B, the resonance current generates mutual inductances 55 
between the pads 14-72 and 14-81 and between the pads 14-72 and 14-91. 
Consequently, an undesired response signal is generated by the stray 
inductance between the pad 14-72 and 14-81 and between the pads 14-72 and 
14-91. This undesired response signal is cancelled by the earth pattern 
portion 8-1. 
That is, the earth pattern portion 8-1 controls the resonance current path 
so as to make the mutual inductances 55 equal. Further, the cut-away 
(non-conductive) areas 64 controls the resonance current path. These 
resonance current path control means equalize the mutual inductances 55, 
whereby the undesired response signals induced to the output signal 
patterns 10-8 and 10-9 are substantially equalized in magnitude. The 
output signal patterns 10-8 and 10-9 are coupled to the inverting and 
non-inverting input terminals (i.e., pads 14-82 and 14-92) of differential 
amplifier 26. In this manner the undesired response generated by stray 
inductance is cancelled by differential amplifier 26. 
Thus, both an undesired response generated by stray capacitance and an 
undesired response generated by stray inductance can be cancelled 
according to this invention. Accordingly, a low pass filter and a high 
pass filter which are formed in an ASF element due to an undesired 
response generated by stray capacitance or stray inductance between the 
input and output terminals of the ASF are eliminated. This means that it 
is possible to effectively use the frequency characteristic of the ASF. 
As shown in FIG. 4, a jumper line 58 which replaces the earth pattern 
portion 8-1 is provided to connect between a pad 14-E5 disposed on earth 
pattern 8 adjacent the pad 14-E2 and a pad 14-E6 disposed also on earth 
pattern 8 but adjacent the pad 14-E3. It is apparent that the jumper line 
58 may be combined with the earth pattern portion 8-1. 
In an area shown as surrounded by dotted line of FIG. 1 on the opposite 
surface of circuit board 4 which is corresponding to the area in which the 
stem or body 40 of acoustic surface wave filter element is positioned on 
the one surface thereof, the earth pattern 8 and the signal patterns 10-7, 
10-8 and 10-9 are arrayed symmetrically of the axis 60 lying on end 
portion of the input signal pattern 10-7 and extending between the output 
signal patterns 10-8 and 10-9. The symmetrical array of patterns permits 
equalization of voltages induced in output signal patterns 10-8 and 10-9 
by a resonance current flowing in earth pattern 8, and of stray 
capacitances between output signal patterns 10-8 and 10-9, voltages 
induced by such stray capacitances in output signal patterns 10-8 and 10-9 
being thus equalized. This is described to that the symmetrical array of 
patterns causes the input signal pattern 10-7 and earth pattern 8 to be 
positioned at an equal distance from both of the output signal patterns 
10-8 and 10-9. It is thus understood that without related patterns being 
arrayed in symmetry, pattern 10-7 and earth pattern 8 can only be arrayed 
equidistantly from patterns 10-8 and 10-9, acceptably to the purpose. 
That portion of earth pattern 8 by which the filter area 44 is encircled 
has a non-conductive area 64 shown as surrounded by a dot-dash line at 62 
so as to change current distribution in earth pattern 8, thereby to 
substantially equalize the voltage induced in output signal patterns 10-8 
and 10-9. 
Care is taken that the respective lead wires or pins 28, 30, 32, 34 and 36 
of acoustic surface wave filter element 24 have preferably a substantially 
equivalent length and protrude equidistantly from the other surface of 
circuit board 4, or pads 14-72, 14-E2, 14-E3, 14-81 and 14-91. This helps 
to ensure equalization of voltages of unnecessary response signals present 
in the output signal patterns 10-8 and 10-9, which will be apparent in 
FIG. 6 hereinafter explained. 
As shown in FIG. 5, moreover, an earth pattern portion 8-2 may be provided 
between the in-parallel extending output signal patterns 10-8 and 10-9 to 
extend in substantially parallel with the latter two. The earth pattern 
portion 8-2 serves to shield the signal patterns 10-8 and 10-9 or 
influences of mutually reversed phase voltages from each other. Further, 
as shown in FIG. 5, a jumper line 58 is provided to extend across the 
input signal pattern 10-7 and connect pads 14-E7 and 14-E8. The jumper 
line 58 functions, combined with the earth pattern portion 8-1, to render 
distribution of the resonance current uniform in earth pattern 8. The 
jumper line 58 functions in the same way as does the earth pattern portion 
8-1. Thus it is not described here how it works. 
As can be understood, the jumper line 58 may be provided on either of the 
surfaces of circuit board 4 in so far as it is not placed in contact with 
signal pattern 10. 
The foregoing arrangements enable the differential amplifier to cancel 
unnecessary response signals when the latter are derived in output signal 
patterns 10-8 and 10-9, while signals derived from propagation in filter 
element to output signal patterns are, because of having phases shifted 
therein, are therein simply amplified for transmission to the subsequent 
stage. 
In a television receiver set having the VIF circuit in which the circuit 
board of the invention is applied, ghost images and beat patterns are 
avoided from occurring since unnecessary response signals are less likely 
to appear in the circuit board. 
Experiments were conducted by the inventor in the following manner to show 
that the circuit board of the invention provide good characteristics of 
television signal frequencies. Referring to the graph of FIG. 6, a curve 
shown by a solid line I is indicative of frequency characteristics of the 
television signal provided by circuit board of the invention, and a curve 
shown by a broken line II is indicative of those provided by a similar 
circuit but wherein the input earthed lead wire 30 has a greater length 
than the other input and the earthing lead wires 28 and 36 to protrude at 
a greater distance than the latter so that stray capacitances between one 
of the output lead wires 32 and 34 are assumed to have a different value 
of stray capacitance relative to the input lead wires 28 and 36 than the 
other output lead wire. It is noted in the graph of FIG. 6 that symbols 
S.sub.0, C, P and S.sub.1 designate sound carrier signal in the reception 
channel, color carrier wave signal in the reception channel, picture 
carrier wave channel in the reception channel, and sound carrier signal in 
the lower channel to the reception one, respectively. Ideal television 
frequency characteristics are represented by curve I of FIG. 6 which was 
provided by circuit board of this invention. Curve II designated by broken 
line indicates an insufficient amount of attenuation of sound carrier 
signal S.sub.1 in the lower channel. It has been generally known that 
sound carrier signal S.sub.1 in the lower channel is required to have more 
than 35 dB of attenuation when color carrier wave signal C in the 
reception channel lies at 0 dB. Whereas curve I shows the attenuation at 
the order of 45 dB, curve II shows the attenuation of sound signal in the 
lower channel, as at S'.sub.1, at the order of 34 dB which can be regarded 
insufficient. Such an insufficient attenuation results in generation of 
beat patterns in a reproduced picture of the television receiver set. 
As FIG. 6 clearly shows, the stray capacitance constitutes a high pass 
filter and fails to completely trap the sound carrier signal S1 in the 
lower channel, thus inevitably causing a beat pattern. The circuit board 
of this invention can thus achieve a television frequency characteristic 
as indicated by curve I in FIG. 6. 
FIG. 7 illustrates how an undesired response is generated by mutual 
inductance. Curve I shows the frequency characteristic of a television 
signal obtained by the circuit board of this invention. Curve II shows the 
frequency characteristic of an undesirable television signal obtained of a 
circuit board without the jumper line 58. If the jumper line 58 is removed 
from the circuit board, the resonance current flowing in the earth pattern 
8 is distributed not uniformly, and the undesired response signals 
generated in the output signal patterns 10-8 and 10-9 come to have 
different levels. Namely, FIG. 7 shows how the frequency characteristic of 
a television signal is changed by the mutual inductance 55. The mutual 
inductance 55 constitutes a low pass filter and fails completely to trap 
the image carrier signal Po in the upper channel, thus inevitably causing 
a ghost image. FIG. 7 clearly shows that the mutual inductance 55 cannot 
fully trap the image carrier signal Po and that the sound carrier signal 
S1 in the lower channel cannot be fully trapped due to the stray 
capacitance if the jumper line 58 is removed. 
It is apparent from the foregoing description that the circuit board of the 
invention, where unnecessary response signals are derived in the two 
signal circuit patterns connected with the output lead wires of an 
acoustic surface wave filter element, can enable the differential 
amplifier to cancel such unnecessary response signals so that the circuit 
board of the invention can be used for the VIF circuit of a television 
receiver set to make ghost images and beat patterns unlikely to occur.