JPH01233834A - Radio receiver facilitating automatic band width control at the time of tuning - Google Patents

Abstract

PURPOSE: To reduce an interoffice trunk noise output by providing a controlling means which responds to a trigger signal and makes a bandwidth means minimize the bandwidth of an audible signal until a required broadcasting signal is tuned in. CONSTITUTION: An IF output of a tuner 12 is supplied to an IF input (pin 5) of a decoder 11, and an input from the tuner 12 is also supplied to a bandwidth control unit 13. The decoder 11 operates so that a variable Q filter in the decoder 11 can perfectly minimize the bandwidth of an audio channel by discharge of a stop detection capacitor 14. Because the unit 13 makes the capacitor 14 discharge during non-tuning of radio, an audio path is substantially restricted about a bandwidth for that time. Thereby, unnecessary sound which results from interoffice trunk noise is almost lost.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates generally to radio receivers, and more particularly to AM radio receivers.

BACKGROUND OF THE INVENTION Radio receivers are well known to those skilled in the art. Such receivers operate to receive broadcast RF low signals. The receiver typically includes a tuning mechanism that can select the particular broadcast signal desired, which can then be demodulated by the radio to produce an audible information signal.

SUMMARY OF THE INVENTION When attempting to tune to a desired broadcast station, receivers typically produce a variety of unpleasant audible noises in response to signals between various channels. A method is needed to reduce interstation noise output when tuning such radios.

SUMMARY OF THE INVENTION This need is substantially met by providing the radio receiver disclosed herein. The radio is provided with a bandwidth control unit that controls the bandwidth of the audible signal output from the radio. When the radio is not tuned to the desired broadcast signal (i.e., when the radio appears to be tuned to such a station, but is actually tuned between stations), the trigger unit generates a trigger signal. . The control unit is responsive to the trigger signal to cause the bandwidth control unit to minimize the bandwidth of the audio signal path until it tunes to the desired broadcast signal. - Once a receivable signal is located, the bandwidth can be increased to allow the radio to operate normally.

In one embodiment of the invention, the bandwidth of the audio signal path can be controlled using a variable Q filter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings and in particular to FIG.
It can be seen that it is shown as 0. The invention 10 may include an AM stereo decoder 11, such as the MC13022 manufactured by Motorola in this embodiment.

Of course, to create a fully operational receiver it is necessary to provide other known components connected in a suitable manner to each output pin of the decoder 11. However, such configurations are well known to those skilled in the art and their description here is not necessary for a better understanding of the invention. Therefore, for the sake of brevity and clarity, these other components and connections are not shown or described herein.

The invention also generally includes an optional tuning device 12 and a bandwidth control unit 13. Tuning device 12 may be a mechanical tuning structure (such as a hand-operated variable capacitor mechanism), an electronically controlled tuning mechanism, or any other tuning mechanism. It is fed to the IF large input pin 5) of the IF ratio output decoder 11 of the tuning device. The output from tuning device 12 is also provided to bandwidth control unit 13 . This output becomes a display signal when the tuning device 12 is performing a tuning operation. This display can be any of a variety of signals depending on the particular tuning device selected and the needs of the application.

Decoder 11 has a stop detect port (pin 6) connected to a suitable capacitor 14.

Similarly, the mixing port (pin 23) of decoder 11 is connected to capacitor 16. The capacitor 16 connected to the mixing port' (pin 23) is an MC1302
'2 (11) supports numerous features. These features are described in U.S. Patent Application No. 121.361, entitled "Multifunction Control Circuit for rAM Stereo Receivers," filed November 16, 1987, and U.S. Patent Application No. 121.361, issued August 18, 1987. 4.688,254 Control of Mixing for an RAM Stereo Receiver. The bandwidth control unit 13 has two capacitors 14 and 1
6 and through these connections certain operating characteristics of the decoder 11 can be controlled.

The decoder 11 includes a variable Q filter in its audio processing circuit. (For details regarding this filter, see 1.
U.S. Patent No. 4,680.79 issued July 14, 987
No. 5 [Dual Purpose Variable Q Filter]. Reference is made to the contents of this patent in this application. , ) This variable filter operates in the decoder 11 to control the bandwidth of the audio circuit as a function of the AGC circuit also provided here. The filter also operates to generate a 10 kHz notch to minimize interference from adjacent channels. As explained in more detail below,
Invention 10 provides a bandwidth control unit 13 so that the variable Q filter limits the bandwidth of the audio path to minimize inter-station noise when the radio is not tuned.

Next, referring to FIG. 2, the bandwidth control unit 13 will be explained in more detail.

When tuned to a station, the mixing fundenna 16 provides a charge of at least 0.7 volts to the mixing boat 22 and the stop detect capacitor 14 provides a high signal (i.e., greater than 1.5 volts) to the stop detect port 21. . 1st
and second comparators 20 and 24 receive the stop detection voltage. The first comparator 20 has a stop detection voltage of 1.
Generates high output when voltage exceeds 5 volts. The second comparator 24 produces a high output when the stop detection voltage exceeds 0.4 volts. When tuned to the station, both comparators (20
and 24) will therefore be higher.

As a result, the first comparator 20
6's reset port, which lowers its Q output. A first NAND gate 27 inverts this low output, causing a first transistor 28 to conduct, thereby energizing a lamp (not shown). This light indicates to the user that the radio is tuned to a station.

When the user begins to tune the radio to another station, an appropriate tune indication signal is generated on the input port 29 to indicate this. This tuning instruction signal connects the enable signal to the two ANs.
D gates 31 and 32 and also makes second transistor 33 conductive.

Once conductive, the second transistor 33 begins to discharge the stop detection capacitor 14.

Once stop detect capacitor 14 has discharged below 1.5 volts, first comparator 20 releases the reset signal from flip-flop 26. If the stop detection capacitor 14 discharges below 0.4 volts, the second comparator 24 transfers the switch signal to the second NAN.
The second signal already enabled through D-gate 34
is supplied to the AND gate 32 of. This second AND gate 32 then provides a high signal through the OR gate 36, causing the third transistor 37 to conduct, thereby discharging the mixing capacitor 16.

Once the mixing capacitor 16 has discharged to less than 0.4 volts, the high signal is already enabled in the first AND, as asserted by the third comparator 38.
A set signal is supplied to the gate 31, which supplies a set signal to the flip 70 tube 26. This allows the flip
The flop 26 is an OR gate 36 and a first NAND gate 2.
7 and a high output signal. The latter gate 27 then shuts off the first transistor 28, thereby extinguishing the tuning lamp.

The decoder 11 operates such that the variable Q filter within the decoder 11 completely minimizes the bandwidth of the audio channel by discharging the stop detection capacitor 14. Since the bandwidth control unit 13 discharges the stop detection capacitor 14 during radio detuning, the audio path becomes substantially limited in terms of bandwidth during the radio detuning, which eliminates most unwanted sounds resulting from interstation noise. It disappears.

-H When the tuning process is completely finished, the signal supplied to the untuned signal port 29 of the band control unit 13 becomes low again. This results in two AND gates 31 and 3
2 and the second transistor 33 are disabled.

As a result, the stop detection capacitor 14 can be charged after tuning to the broadcast station. Mixing capacitor 16 remains fully discharged to prevent the predetermined stereo signal from appearing prematurely. When you tune into a broadcast station,
The voltage on the stop detection capacitor 14 increases and ultimately becomes higher than 1.5 volts, which causes the first comparator 2
0 resets flip-flop 26 and third transistor 37 is turned off. This allows the mixing capacitor 16 to operate normally. Also, when the flip-flop 26 is reset, the first transistor 2
8 becomes conductive again, illuminating the tune lamp, thereby providing a visible indication to the user that the radio is tuned.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a radio receiver that is an embodiment of the present invention. FIG. 2 is a detailed circuit diagram of the bandwidth control unit of FIG. 1. 11... Decoder, 12... Tuning device, 13...
・Bandwidth control unit, 14.16...Capacitor, 23.24...Comparator, 27.34...NAND gate, 28.33.37...Transistor, 36...OR
Gate.

Claims (1)

[Claims] 1. RF means for receiving a desired broadcast signal, tuning means for selecting a desired specific broadcast signal, and demodulation means for demodulating the desired specific broadcast signal to obtain an information signal. , audio means for rendering said information signal into an audible signal, further comprising: A) bandwidth means for controlling the bandwidth of said audible signal; B) generating a trigger signal when said tuning means is not tuned to a desired broadcast signal. and C) control means responsive to the trigger signal for causing the bandwidth means to minimize the bandwidth of the audible signal until the desired broadcast signal is tuned. radio receiver. 2. The radio receiver according to claim 1, wherein the bandwidth means comprises a variable Q filter. 3. A method of minimizing inter-station noise while tuning the receiving broadcast signal in a radio receiver that receives a broadcast signal and converts the broadcast signal into an audio signal, the method comprising: B) reducing the bandwidth of the audio signal when the radio receiver is not tuned to a broadcast signal; and C) detecting when the radio receiver is not tuned to a broadcast signal. A method comprising: increasing the bandwidth of the audio signal when tuned.