Acoustic wave band-pass filter with low loss LC notch matching network
A band-pass filter (BPF) having first and second ports includes an acoustic wave filter (AWF) having first and second ports, the first port of the AWF coupled to the first port of the BPF. An impedance matching network consisting of a first inductor in parallel with a series combination of a second inductor and a capacitor is connected across the first port of the BPF.
1. A band-pass filter (BPF) having first and second ports, comprising:
an acoustic wave filter (AWF) having first and second ports, the first port of the AWF coupled to the first port of the BPF; and
an impedance matching network connected across the first port of the BPF, the impedance matching network consisting of a first inductor in parallel with a series combination of a second inductor and a capacitor, wherein
the impedance matching network is configured to match an impedance of the first port of the AWF to a target impedance, and create a transmission minimum at a frequency outside of a passband of the AWF, and
inductances of the first and second inductor are related by the formula:
L
1
=
L
a
L
2
(
1
-
(
f
n
o
t
c
h
/
f
0
)
2
)
(
L
2
(
1
-
(
f
notc
h
/
f
0
)
2
)
-
L
a
)
where L 1 and L 2 are the inductances of the first and second inductors, respectively, f notch is the frequency of the transmission minimum, f 0 is a selected frequency within a passband of the AWF, and L a is an inductance of a hypothetical inductor required to match an impedance of the first port of the AWF to a target impedance value at the frequency f 0 .
2. The band-pass filter of claim 1 , wherein L 2 and a capacitance of the capacitor are related by the formula:
f
n
o
t
c
h
=
1
2
π
L
2
C
1
where C 1 is the capacitance of the capacitor.
3. The band-pass filter of claim 2 , wherein C 1 , L 1 , and L 2 are selected to minimize an insertion loss of the BPF at some or all frequencies within the passband.
4. The band-pass filter of claim 1 , wherein one or more of the first inductor, the second inductor, and the capacitor are realized in a package structure of the BPF.
5. The band-pass filter of claim 1 , wherein one or more of the first inductor, the second inductor, and the capacitor are external to a package structure of the BPF.
6. A band-pass filter, comprising:
an acoustic wave filter (AWF) having first and second ports, wherein
the first port of the AWF has an impedance Z a that can be matched to a first target impedance at a frequency f 0 within a passband of the AWF by connecting an inductor with an inductance L a across the first port, and
the second port of the AWF has an impedance Z b that can be matched to a second target impedance at frequency f 0 by connecting an inductor with an inductance L b across the second port; and
an impedance matching network connected across the first port, the impedance matching network consisting of a first inductor in parallel with a series combination of a second inductor and a capacitor, wherein
the impedance matching network is configured to match Z a to the first target impedance at frequency f 0 and create a transmission minimum at a frequency outside of the passband of the AWF, and
inductances of the first and second inductor are related by the formula:
L
1
=
L
a
L
2
(
1
-
(
f
n
o
t
c
h
/
f
0
)
2
)
(
L
2
(
1
-
(
f
notch
/
f
0
)
2
)
-
L
a
)
where L 1 and L 2 are the inductances of the first and second inductors, respectively, and f notch is the frequency of the transmission minimum.
7. The band-pass filter of claim 6 , wherein L 2 and a capacitance of the capacitor are related by the formula:
f
n
o
t
c
h
=
1
2
π
L
2
C
1
where C 1 is the capacitance of the capacitor.
8. The band-pass filter of claim 7 , wherein C 1 , L 1 , and L 2 are selected to minimize an insertion loss of the BPF at some or all frequencies within the passband.
9. The band-pass filter of claim 6 , wherein one or more of the first inductor, the second inductor, and the capacitor are realized in a package structure of the BPF.
10. The band-pass filter of claim 6 , wherein one or more of the first inductor, the second inductor, and the capacitor are external to a package structure of the BPF.