JPH02305120A - Intermediate frequency circuit for receiver - Google Patents

Abstract

PURPOSE:To improve the selectively by providing an adjacent disturbing signal eliminating means suppressing an adjacent disturbing signal component included in an intermediate frequency signal with a signal component passing through a filtering means. CONSTITUTION:Second and 3rd BPFs 4, 5 act like filtering means passing a signal component corresponding to the adjacent disturbing signal component of an IF signal passing through a 1st BPF 4 as a filtering means. Moreover, 1st and 2nd operational amplifiers 3, 6 act like an adjacent disturbing signal eliminating means suppressing the adjacent disturbing signal component included in the IF signal passing through the 1st BPF 2 with a signal component passing through the 2nd and 3rd BPFs 4, 5. Thus, the adjacent disturbing signal component of 10.4MHz+ or -150kHz of the IF signal passing through the 1st BPF 2 being a broad band BPF is suppressed by the 1st operational amplifier 3 and the adjacent disturbing signal component of 11.0MHz+ or -150kHz of the IF signal passing through the 1st BPF 2 being a broad band BPF is suppressed by the 2nd operational amplifier 6 to improve the selectively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an intermediate frequency (IF) circuit for a receiver, and more particularly to an intermediate frequency circuit with improved selectivity in an FM receiver.

[Conventional technology]

Conventionally, in order to improve selectivity in an IF circuit, I
Only the desired signal is passed through an F-fold signal narrowband bandpass filter (BPF), or a trap circuit is provided to remove interfering signals adjacent to the desired signal.

[Problem to be solved by the invention]

However, as mentioned above, when the IF multiplied signal is passed through a narrowband BPF or trap circuit, the group delay of the desired signal worsens.
Particularly in the case of an FM receiver in which the IF multiplied signal carries signal information depending on its frequency, if group delay occurs in the desired signal as described above, distortion will occur in the detected output signal.

Therefore, in view of the above-mentioned conventional problems, it is an object of the present invention to provide an intermediate frequency circuit for a receiver that improves selectivity without causing distortion to a desired signal.

[Means to solve the problem]

In order to solve the above problems, an intermediate frequency circuit of a receiver made according to the present invention includes a filter means for passing a signal component corresponding to an adjacent interference signal component of an intermediate frequency signal, and an adjacent interference signal component included in the intermediate frequency signal. The present invention is characterized by comprising adjacent interference signal removing means for suppressing the interference signal component by the signal component passed through the filter means.

[Effect]

In the above configuration, the filter means passes a signal component corresponding to the adjacent interference signal component of the intermediate frequency signal, and the adjacent interference signal removing means removes the adjacent interference signal component included in the intermediate frequency signal from the filter means. Since the desired signal component is suppressed by the signal component passed through the filter, the selectivity is improved, and since the desired signal component is not passed through the narrow band filter means, the phase shift due to group delay is minimized, reducing distortion. No deterioration occurs.

Therefore, selectivity can be improved without causing distortion in the desired signal.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a block diagram showing an embodiment of an intermediate frequency circuit of a receiver according to the present invention. In the figure, a front end 1 selects a desired broadcast signal from radio waves received by an antenna, and selects the desired broadcast signal. The received broadcast signal is converted into an IF signal of, for example, 10.7 MHz and output. The above IF multiplied signal, 10.
Broadband first BP with center frequency fC at 7MHz
The signal is passed through F2 to remove interference waves. Wideband BPF2
The output signal of the first operational amplifier 3 has a center frequency fc of, for example, 10.4M11z and a passband width B.
A second BPF 4 with a characteristic w of e.g. 300 k&
and the input of a third BPF 5 having characteristics such that the center frequency fc is, for example, 11.0 MHz and the passband width Bw is, for example, 300 k&.

The output signal of the second BPF 4 is input to the operational amplifier 3, and the output of the first operational amplifier 3 includes the IF multiplied signal that has passed through the broadband first BPF 2 and the second BPF 4.
10.4M) (z±150 kHz signal component is subtracted) and the signal is output.

The output signal of the first operational amplifier 3 is
The output signal of F5 is inputted to the input terminal of the second operational amplifier 6, and the output signal of the first operational amplifier 3 is inputted to the output signal of the second operational amplifier 6. OMitz±1
A signal with the 50 kHz signal component subtracted is output.

The output signal of the second operational amplifier 6 is input to the FM detector 7, where it is FM detected and converted into an audio signal, amplified by an amplifier (not shown), and then supplied to a speaker.

The second and third BPFs 4 and 5 function as filter means for passing a signal component corresponding to the IF multiplied signal adjacent interference signal component that has passed through the first BPF 2 as a filter means, and Operational amplifiers 3 and 6 are
It functions as an adjacent interference signal removing means that suppresses the adjacent interference signal component included in the IF multiplied signal passed through the first BPF 2 by the signal component passed through the second and third BPFs 4 and 5.

In the above configuration, the IF multiplied signal passed through the broadband first BPF 2, the first operational amplifier 3 receives 10.4 M7±150, and the second operational amplifier 6 receives 11.0 MHz+.
Adjacent interference signal components of 150 kHz are suppressed, improving selectivity. Further, the desired signal component is the broadband first BPF 2L.

Since it is not passed through a narrow band filter,
Phase rotation due to group delay is minimized, and no deterioration of distortion occurs.

In addition, in order to correct the delay caused by the second and third BPFs 4 and 5, the second and third BPFs 4 are connected between the output of the broadband first BPF 2 and the power of the first operational amplifier 3.
A delay circuit having a delay time corresponding to the delay occurring in and 5 may be inserted.

In addition, in order to more completely cancel out adjacent interference components in the first and second operational amplifiers 3 and 6, the second and third B
Insert an amplifier and volume into the outputs of PF4 and 5,
The level of the adjacent interference component input to each of the first and second operational amplifiers 3 and 6 may be adjusted appropriately.

Furthermore, in order to enable better reception when there is no adjacent interference, switches are inserted into the outputs of the second and third BPFs 4 and 5, respectively, and the switches are turned off when there is no adjacent interference to operate in a wide band. You may also do so.

Furthermore, instead of the two first and third BPFs 4 and 5, a filter having rabbit ear characteristics as shown in FIG. 2, which is used as an SrF filter in the TV field, may be used. If you do this,
One operational amplifier is sufficient.

Note that it is also possible to digitally perform the above-described operation using a high-speed digital signal processing circuit.

〔effect〕

As explained above, according to the present invention, the desired signal component does not pass through the narrow band filter means, so the phase rotation due to group delay is minimized, and distortion does not worsen, and the desired signal is not distorted. It is possible to improve the selectivity without causing any problems.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of an intermediate frequency circuit of a receiver according to the present invention, and FIG. 2 is a diagram showing filter characteristics used in a partial modification of FIG. 1. 3.6... Adjacent interference signal removal means (first and second operational amplifiers), 4.5... Filter means (second and third operational amplifiers)
BPF).

Claims (1)

[Scope of Claims] Filter means for passing signal components corresponding to adjacent interference signal components of an intermediate frequency signal; and filter means for passing adjacent interference signal components included in the intermediate frequency signal,
An intermediate frequency circuit for a receiver, comprising adjacent interference signal removing means for suppressing a signal component passed through the filter means.