Telecommunications – Receiver or analog modulated signal frequency converter – Noise or interference elimination
Reexamination Certificate
2000-12-29
2003-11-11
Vo, Nguyen T. (Department: 2685)
Telecommunications
Receiver or analog modulated signal frequency converter
Noise or interference elimination
C455S338000
Reexamination Certificate
active
06647253
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an intermediate frequency input circuit, and more particularly, relates to an intermediate frequency input circuit, which is coupled between output nodes of a frequency mixing circuit and input nodes of an intermediate frequency amplifier circuit, in which an intermediate frequency characteristic of a selector channel and trap characteristics of the intermediate frequency components of the upper and lower adjacent channels can be selected.
2. Description of the Related Art
In some television tuners, an intermediate frequency input circuit is connected between output ends of a frequency mixing circuit and input ends of an intermediate frequency amplifier circuit. The intermediate frequency input circuit allows a selective intermediate frequency signal of a selector channel to pass while rejecting undesired frequency components that may occur near the intermediate frequency. A rejected frequency component may include an intermediate frequency component of an upper adjacent channel and an intermediate frequency component of a lower adjacent channel. Accordingly, undesired frequency components are not received by the intermediate frequency amplifier circuit.
FIG. 4
shows an example of a known intermediate frequency input circuit. As shown, an intermediate frequency input circuit
41
is connected between a frequency mixing circuit
42
and an intermediate frequency amplifier circuit
43
. The intermediate frequency input circuit
41
includes a pair of input ends
41
1
and
41
2
, a pair of output ends
41
3
and
41
4
, a power supply terminal
41
5
, a first capacitor
44
, a first inductor
45
having a center tap, a second capacitor
46
, a second inductor
47
, a third inductor
48
, a third capacitor
49
, a fourth capacitor
50
, a first resistor
51
, a fifth capacitor
52
, and a second resistor
53
. The frequency mixing circuit
42
includes a pair of output ends
42
1
and
42
2
and a pair of output transistors
54
and
55
in a common-base configuration. The intermediate frequency amplifier circuit
43
includes a pair of input ends
43
1
and
43
2
and a pair of input transistors
56
and
57
in a common-emitter configuration.
In the intermediate frequency input circuit
41
, the first capacitor
44
and the first inductor
45
are connected in parallel between the pair of input ends
41
1
and
41
2
. The center tap of the first inductor
45
is connected to the power supply terminal
41
5
. A parallel circuit that includes the second capacitor
46
and the second inductor
47
is between one input end
41
1
and one output end
41
3
. This parallel circuit is connected to the fourth capacitor
50
, and the first resistor
51
in series. Between the other input end
41
2
and the other output end
41
4
is a second parallel circuit that includes the third inductor
48
and the third capacitor
49
. The second parallel circuit is connected to the fifth capacitor
52
, and the second resistor
53
in series. In the frequency mixing circuit
42
, a collector of the output transistor
54
is connected to one output end
42
1
, and a collector of the output transistor
55
is connected to the other output end
42
2
. In the intermediate frequency amplifier circuit
43
, a base of one input transistor
56
is connected to one input end
43
1
, and a base of the other input transistor
57
is connected to the other input end
43
2
. The pair of input ends
41
1
and
41
2
of the intermediate frequency input circuit
41
is connected to the pair of output ends
42
1
and
42
2
of the frequency mixing circuit
42
. The pair of output ends
41
3
and
41
4
of the intermediate frequency input circuit
41
is connected to the pair of input ends
43
1
and
43
2
of the intermediate frequency amplifier circuit
43
.
In the intermediate frequency input circuit
41
, the capacitance of the first capacitor
44
and the inductance of the first inductor
45
are selected so that the first capacitor
44
and the first inductor
45
are in resonance with an intermediate frequency of a selector channel. The capacitance of the second capacitor
46
and the inductance of the second inductor
47
are selected so that the second capacitor
46
and the second inductor
47
are in resonance with an intermediate frequency component of an upper adjacent channel, thus forming a first trap circuit for trapping the intermediate frequency component of the upper adjacent channel. The capacitance of the third inductor
48
and the inductance of the third capacitor
49
are selected so that the third inductor
48
and the third capacitor
49
are in resonance with an intermediate frequency component of a lower adjacent channel, thus forming a second trap circuit for trapping the intermediate frequency component of the lower adjacent channel.
The known intermediate frequency input circuit
41
operates as follows. An intermediate frequency signal (hereinafter referred to as an “IF signal”) of the selector channel, which includes the unnecessary frequency components, is passed through the pair of output ends
42
1
and
42
2
of the frequency mixing circuit
42
. The IF signal is received by the intermediate frequency input circuit
41
. In the intermediate frequency input circuit
41
, the resonance circuit that includes the first capacitor
44
and the first inductor
45
selects an intermediate frequency of the selector channel from the IF signal. The first trap circuit, which includes the second capacitor
46
and the second inductor
47
, traps an intermediate frequency component of the upper adjacent channel of the selected intermediate frequency, which is above and adjacent to the selector channel frequency. The second trap circuit, which includes the third inductor
48
and the third capacitor
49
, traps an intermediate frequency component of a lower adjacent channel of the selected intermediate frequency, which is below and adjacent to the selector channel frequency. The IF signal that passes through the first trap circuit passes through the fourth capacitor
50
, which is a coupling capacitor. The first resistor
51
adjusts the amplitude of the IF signal, and the IF signal is supplied to one output end
41
3
. Simultaneously, the IF signal that passes through the second trap circuit passes through the fifth capacitor
52
, which is a coupling capacitor. The second resistor
53
adjusts the level of the IF signal, and the IF signal is passed to the other output end
41
4
. The IF signal obtained at the pair of output ends
41
3
and
41
4
is received by the pair of input ends
43
1
and
43
2
of the intermediate frequency amplifier circuit
43
, and the input IF signal is amplified by the pair of input transistors
56
and
57
.
FIG. 5
shows an example of a frequency characteristic of the intermediate frequency input circuit
41
shown in FIG.
4
. In
FIG. 5
, reference symbol P denotes a picture frequency in the intermediate frequency range of the selector channel. Reference symbol S denotes a sound frequency in the intermediate frequency range of the selector channel. Reference symbol T
1
denotes the intermediate frequency component of the lower adjacent channel (N−1) of the selector channel (N). Reference symbol T
2
denotes the intermediate frequency component of the upper adjacent channel (N+1) of the selector channel (N).
Referring to
FIGS. 4 and 5
, the known intermediate frequency input circuit
41
has a selective characteristic for the intermediate frequency of the selector channel, and has separate trap characteristics for the intermediate frequency components of the lower adjacent channel and the upper adjacent channel. The difference in amplitude between the peak amplitude of the intermediate frequency of the selector channel and the trap amplitude of the intermediate frequency component of the lower adjacent channel is approximately 11.4 dB in this circuit. The difference in amplitude between the peak amplitude of the intermediate frequency of the selector channel an
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Vo Nguyen T.
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