KR800000054B1 - Am-fm receiver having improved filtering - Google Patents

Abstract

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Description

Radio receiver for AM-FM receiver

1 is a block diagram schematically showing the AM-FM receiver of the present invention;

2 is a complete circuit diagram of a receiver of the present invention except for an AM-FM detector and an audio amplifier.

The present invention relates to an AM-FM receiver in a superheterodyne receiver, which can use a common filter capacitor for supplying bias (voltage, current), AGC function in AM operation, and AFC function in FM operation. It relates to an AM-FM receiver.

The B + bias is supplied by a variable current source (controllable current source) that adjusts the bias according to the detector output. In the FM mode, automatic frequency control of the local oscillator is performed by bias adjustment.

In AM mode, automatic gain control of the amplifier and tuner AM sections is achieved by bias adjustment.

The present invention consists of an integrated circuit.

The present invention relates to an AM-FM superheterodyne receiver, in which a simple circuit for achieving the required automatic frequency and automatic gain control function is formed. In addition, the present invention relates to the integrated circuit of the receiver, which is to increase the complexity of the chip itself, but to reduce the complexity of the number of chips.

Radio receivers for AM and -FM operation have been made using semiconductor devices for some time. However, with the advent of integrated circuits, the use of individual transistors is on the decline. In general, integrated circuits in which active and passive elements are formed of monolithic semiconductor chips have been provided as individual functional elements of a radio receiver such as an audio amplifier and an intermediate frequency amplifier. All functions are done on a single chip, with separate filters used for AFC, AGC and bias supplies.

The present invention uses the same principles as described above, but in the aftermath of mode conversion and control functions and in bias supply.

It is an object of the present invention to provide a new AM-FM receiver, and to provide a new AM-FM receiver that allows mode conversion to be effectively performed, and uses a new filter device for automatic gain control and automatic frequency control. And to provide an AM-FM radio receiver for B + bias decoupling.

It is also an object of the present invention to provide an AM-FM radio receiver which is useful for automatic gain control, automatic frequency control, and B + bias decoupling using a common filter. It consists of a single tuner that converts to an intermediate frequency. The FM section of the tuner has a first terminal for connecting to a DC bias voltage source, a local oscillator that is excited through this terminal and can be tuned by voltage control. An intermediate frequency amplifier for two intermediate frequency signals excited through a second terminal for connection to a bias voltage source, the amplifier having at least one amplified bomb controlled by a bias voltage change;

When the FM signal is detected, it generates a DC voltage for AFC control proportional to the frequency deviation, and when the AM signal is detected, an AM-FM detector for the intermediate frequency signal to generate a DC voltage for AGC control proportional to the amplitude. The purpose is to provide a new device consisting of.

A bias supply is also provided, which is a device that excites from a primary supply of DC bias voltage.

It is coupled to an energy induction device for controlling the bias voltage applied to the terminal, but consists of a device having a constant current source that can be controlled. This control device performs primary control to generate low average bias for AM operation and high average bias for FM operation, and responds to the detector output for controlling the bias with these fungal bias as a function of the detector output. Second control

Finally, a capacitance and mode switch device is formed, in the selected form of which one terminal is integrated with the two terminals for filter operation for automatic frequency control and automatic gain control and also for the intermediate frequency amplifier. There is one capacitor that allows bias decoupling.

This mode switch unit converts the tuner, bias supply and AM-FM detector into AM or FM operation. Detailed description of the configuration and effects of the present invention by the accompanying drawings as follows.

The radio receiver which actually uses the present invention is simply shown in a block diagram of FIG. This radio receiver takes the form of a general superheterodyne receiver and has been tried for AM-FM operation. Of particular interest among these characteristics is the automatic frequency control and automatic gain control filter operations. Switching the signal to a pair of fixed intermediate frequencies is done at the portion indicated by the "front end" or tuner 11, 12, 13 of the receiver.

The FM mixer is shown as an input terminal 14, supplied from a whip antena, to which the FM signal is supplied, while the AM mixer is shown except for the external structure for receiving the AM signal. The AM mixer usually depends on the pick-up of the ferrite element contained in the device. The FM mixer 11 receives the local oscillation from the FM local oscillator 12, forms an output at a fixed intermediate frequency (10.7 MHz) and station selection is made in the filter 15 connected to the output. The AM mixer 13, which also includes an oscillator, produces an output at a fixed intermediate frequency of 455 KHz. The AM output is applied to the intermediate frequency filter 16. The AM mixer uses a pair of AGC connections as two conductive wires 18 and 19. The function thereof is described in detail below. Although not shown here, the tuner provides an AM or FM mode operation device along with other mode selection elements of the radio receiver.

The filtered intermediate frequency output from the FM filter 15 or the AM filter 16 is then applied to the input of the intermediate frequency amplifier, the connection of which will be described in detail below.

The intermediate frequency amplifier consists of several stages and provides a substantial direct current feedback. It has pairs of individually connected transistors (Q ₁ , Q ₂ ); (Q ₅ , Q ₆ ); and (Q ₇ , Q ₈ ). The input signal is applied to the base of the transistor Q _l to which the emitter is grounded via a load resistor 17 and the conductor 18 coupled to create a B + bias. The lead 18 is also used for automatic gain control at the individual stages of the intermediate frequency amplifier as described below. The output of Q ₁ appears between the emitter and the load resistor 17, which is there is applied to the emitter of the (Q _2). the base of (Q ₂₎ is generated in the balanced bias each stage and also coupled to a second control wire (19) of which is used for 2AGC.

The lead 19 is bypassed to the earth by one fi1ter capacitor 31. The collector of Q ₂ is coupled to the lead 18 via a load resistor 20. The signal output applied to the collector of transistor Q ₂ together with the step interference of the intermediate frequency amplification is applied to the next transistor Q ₅ and then to the last stage of the intermediate frequency amplification. This stage has the same structure as the first stage and also performs automatic gain control. In particular, the input signal is applied to the base of (Q ₅ ), the collector is connected to the conducting wire (18) for B + bias and gain control, and the emitters of (Q ₅ ) and (Q ₆ ) are connected to each other so that the load resistance (21) Is applied to Earth through

The signal defects from (Q ₅ ) and (Q ₆ ) are made by this interconnection. The base of (Q ₆ ) is connected to the second automatic gain control lead (19) and the collector of (Q ₆ ) has a load resistance. It is connected to the 1st control lead 18 through 22. As shown in FIG.

In the intermediate frequency amplifier, feedback is performed to reduce the deviation so that the DC feedback resistor 23 is coupled between the collector of the transistor Q ₆ and the base electrode. The feedback resistor 23 is coupled to a second automatic gain control lead 19 which is coupled to the second transistor of any of the simplest in a similar manner as is coupled to the base of the second transistor Q ₂ in the initial intermediate frequency step. Combined. The direct current connection allows the control lead 19 to have a voltage that varies with the direct current voltage present on the control lead 18, and provides a convenient method for additional automatic gain control in the tuner of the AM mode.

The output signal amplified at one of the two intermediate frequencies by these connections appears at the collector of transistor Q ₆ and is also applied to the last stage of the intermediate frequency amplification. The last intermediate frequency stage uses transistors Q ₇ and Q ₈ . They are individually connected (Q ₇ ) and the base of (Q ₆ ) is coupled to the collector of (Q ₆ ) and the base of Q ₈ is coupled to the second automatic gain control lead (19). (Q ₇ ) of (Q ₈ ) The emitters are connected to each other and to earth via a power source 24. At each of these intermediate frequencies, the output represented by (Q ₈ ), one of the collectors of (Q ₇ ) (Q ₈ ) containing the AM signal, is a signal coupled to the AM-FM detector 26 for the last filter. Is applied to a suitable tuning circuit 25 for this purpose. The AM-FM detector 26 is designed to be provided for detecting either AM or FM according to the scheme selection and generates an output voltage containing audio and unfiltered intermediate frequency components. In particular, in the AM mode, a DC output voltage proportional to the AM carrier appears, but in the FM mode, the output voltage is proportional to the FM error in the center tuning.

The output voltage detected by the detector 26 is coupled to the audio amplifier 27 after being filtered to remove the high frequency components. The audio amplifier then generates an output to free the loudspeakers 28 coupled to the capacitor. The output detected by the AM-FM detector 26 is combined with a DC level selectable by a device belonging to the AM-FM detector 26 portion, and the controllable power supply 29 responds to both. The power supply 29 then supplies the conductor 18 with a "controllable" current as a function of the detected output quantity. DC level selection is directly related to the mode selection, so the AM action is lower (1.65 volts) and the FM operation is higher (2.4 volts).

As the detected signal meets this condition, the voltage is made on the conductor 18 in two ranges. As will be seen in detail below, the AM voltage condition is selected so that the intermediate frequency amplifier stage exhibits a substantial gain variation. The FM voltage range condition produces higher intermediate frequency gains, but there are some gain variations due to the change of direct current proportional to the automatic frequency control voltage. Since these changes are relatively small and only happen when the automatic frequency control loop is turned on and off, the variation is not a problem. Therefore, the voltage condition for FM is to make the necessary variation at B + for automatic frequency control of the FM local oscillator.

Below is a summary of the overall control of the AM and FM mode. The first control lead 18 creates a B + bias for the FM mixer and the FM local oscillator, and creates a B + bias for the intermediate frequency amplifier stages Q ₁ and Q ₂ , Q ₅ and Q ₆ . It performs five functions: automatic frequency control of the oscillator, automatic gain control of the intermediate frequency stages, and finally automatic gain control of the AM mixer.

The main function of the second automatic gain control lead 19 is to ensure the DC stability of the intermediate frequency amplifier, but also to add automatic gain control of the AM mixer.

Enhancing the functions for the lead 18, only one capacitor coupled to the lead 18 performs various functions. Capacitor 30 (400µf, 4V) is that capacitor.

The capacitor 30 has a value selected to provide the necessary B + bypass for the intermediate frequency stage connected thereto, and performs auto gain control and auto frequency control filtering. The value is chosen to have the required auto gain control time function for AM and the required auto frequency control function for FM. The AM and FM time functions are usually chosen to have the same value, and these values are suitable for dial tuning and are usually half a second. The time functions are therefore suitable for intermediate frequency decoupling and ripple filtering.

The practical use is shown in great detail in FIG. This design was made for integrated circuit fabrication.

The filters for AM-FM tuner signal separation and control are isolated from the chip. The remainder of the receiver, including the intermediate frequency gain strip, second detector, audio amplifier and controllable power supply, is connected to the chip. For simplicity, the internal structure of the AM-FM tuning circuit 25, the AM-FM detector 26, and the audio amplifier 27 are not shown. AM-FM detectors can take several forms.

Now back to Figure 2, the FM mixer is shown in the lower left in the drawing. The FM signal is coupled to the input terminal 14 and to the base of the mixer transistor Q ₁₁ via an input tuning circuit 40. The emitter of Q _l1 is grounded and the collector is connected to the output tuning circuit 41. Coupled to the base of the intermediate frequency transistor Q _l . The signal appearing at the base of the mixer transistor Q _l1 is mixed with the oscillation from the local oscillator.

The FM local oscillator comprises a transistor Q ₁₂ coupled in an emitter common ground and a tank circuit 42 coupled to the collector. The oscillation from the local oscillator is coupled to the base of Q _l1 via a capacitor 43.

The selection of the FM mode is made by the switch device 44. In the AM position, the switching device 44 removes the B + bias supplied by the lead 18 from both the mixer transistor Q _l1 and the local oscillator transistor Q ₁₂ . In the FM position, 2.4 volts on the conducting wire 18 are applied to the collector of the local oscillator Q ₁₂ via the primary circuit of the output tuning circuit 41 and the tank circuit 42.

Appropriate base biases are also provided for both (Q _ll ) characters (Q ₁₂ ). The configuration of the detector and the local generator is essentially the same as that except that the circuit frequency remains independent of the B + bias and there is no effort to remove its independence. The circuit values shown are intended for a properly responding automatic gain control operation and meet the requirements of a typical home receiver. The AM detector is shown in the upper left portion of the figure. This is a four quadrant multiplier with individually paired transistors, i.e. top (Q ₁₃ ) (Q ₁₄ ); (Q ₁₅ ) (Q ₁₆ ); and bottom (Q ₁₇ ) (Q ₁₈ ). ) The AM signal from the input tuning circuit is applied to the base of the transistor Q ₁₇ at the bottom. The other base of the other lower transistor is coupled to the second automatic gain control lead 19 and bypassed to earth by the capacitor 3l. The emitters in paired (Q ₁₇ ) (Q ₁₈ ) are returned to Earth through a power source (CS) under delayed auto gain control. The controlled power supply CS is composed of a transistor Q ₁₉ diode D ₁ and resistors 47 and 48. Transistor Q ₁₉ grounds its emitter, and its base is coupled to the FM terminal of switch 32 via diode D ₁ and resistor 48.

During AM operation, a switch couples (32) to the automatic gain control lead (18). The collector of (Q _l9 ) is coupled to the emitters of (Q ₁₇ ) and (Q ₁₈ ) via a resistor (47). . Therefore, the power supply CS, which is adjusted only by exceeding the delay circuit due to the drop in the diode D ₁ , provides additional automatic gain control to the AM mixer.

Continuing with the top of the AM mixer, the paired transistors (Q ₁₃ ) (Q ₁₄ ) and (Q ₁₅ ) and (Q ₁₆ ) are their paired emitters from (Q ₁₇ ) (Q ₁₈ ) AM signals are received and local oscillator injections are taken into their bases.

The local oscillator contains a pair of individually connected transistors (Q ₂₀ , Q ₂₁ ), the emitters of which are coupled to earth through power supply (Q ₂₂ ) and the collectors are 6 volt B + bias through small resistors (100 ohms). To regress.

The transistors Q ₂₀ and Q _2l are coupled to the collector and base _alternately with each other, and the collector of Q ₂₀ is coupled to the oscillation tank circuit 49. The oscillator output is coupled to the base of the upper transistors Q ₁₄ , Q ₁₅ where mixing from Q ₂₀ takes place. The mixer output is derived from the collector of Q _l6 and is applied to the base of the transistor Ql via the FM tuning circuit 41 via the tuning circuit 50. The mode switch 32 controls the AM portion of the tuner.

The mode switch 32 is a double draw switch in which one terminal is grounded and the other is coupled to the conductive wire 10.

This pole is coupled to the diode D ₁ via a resistor 48. When the mode switch 32 is placed in the earth position, the diode D ₁ is back biased and the current injection from the power supply Q ₁₉ is disconnected, thus disconnecting all currents going to the AM mixer.

On the other hand, operating the switch 32 in a different position causes the current to flow into the power supply Q ₁₉ and causes the AM portion of the tuner to operate. The mode selection switches 32 and 44 operate simultaneously. The intermediate frequency amplifier has already been described in detail except for the addition of an amplifier stage.

The controlled power source 29 is in the lower right part of FIG.

It consists of transistors Q ₂₃ to Q ₂₇ and resistive and capacitive components 51 and 58. It consists of a controllable current reference and a power source controlled by that reference. First, let's talk about the reference. A controllable reference is a transistor (Q ₂₃₎ connected as a diode and connected to the emitter B + conductor through the resistor 51 (+6 volts) current path through an (Q ₂₃₎ is through the two paths that Go to Earth and finish. One path is through Q ₂₄ and the current is subsequently controlled through Q ₂₅ .

The emitter at Q24 is controlled via a resistor 52. The emitter of Q ₂₄ returns to earth through resistor 52 and its base maintains a constant value of +1.2 volts by connection to a bias source coupled to pad 53.

The pad 53 is also provided with a large capacity filter capacitor 54: 160μf for hum reduction and signal decoupling associated with the audio amplifier.

At Q ₂₄ the current flow is controlled by Q ₂₅ depending on the receiver output. The output of the AM-FM receiver is coupled to the base of (Q ₂₅ ) and its emitter is connected to the emitter load resistance of (Q ₂₅ ) through a 600 ohm resistor (55).

Base of the (Q ₂₅₎ is the collector is to +1.2 volts. (Q ₂₅₎ in the pad 53 through the resistor 56 is coupled to a positive bias source through a load resistor (57). Thus, the signal detected from the AM-FM detector 26 is coupled to the base of (Q ₂₅ ) and a change derived from the signal at the emitter current of (Q ₂₄ ) is generated by the emitter load coupling shared therein. The corresponding change is also made to the reference current of (Q ₂₃ ). This mechanism operation works in both AM and FM, causing a change in the current flow of current reference (Q ₂₃ ).

The presence of (Q ₂₅₎ the emitter resistance (55) in the path of the by (Q ₂₅₎ reduced compared to that of the at Veb (the emitter and the base potential difference between) the (Q ₂₄₎ in the first, the (Q ₂₄₎ Tends to produce a higher current at. This produces the lowest repetition current (Q ₂₃ ). The mode selection of Q ₂₃ is provided by transistor Q ₂₆ to control from low personal conditions for AM to high personal conditions for FM. The collector of (Q ₂₆ ) is coupled to the base collector of (Q ₂₃ ) and the base returns to +1.2 volt bias in pad 53.

The emitter of Q ₂₆ is connected to the FM mode switch 32 pole via a resistor 58. Making the switch for FM mode operation (Q ₂₆ ) become conductive and change the current at (Q ₂₃ ) to a new plateau, thus changing the voltage on conductor 18 Raise about 3 volts.

Changing the pole of the mode selector 32 to the AM position turns off (Q ₂₆ ) and reduces the current to the first one. When this mode switch is on both sides, the current at (Q ₂₃ ) is controlled by the received output but in a different current range.

The final element in the controllable power supply 29 is the power supply itself. It is a transistor (Q ₂₇ ) whose emitter is coupled to the positive bias source via a resistor (57), its base is coupled to the base-collector of (Q ₂₃ ) and the collector is also coupled to the lead (18). Therefore, the input contact of the (Q ₂₇₎ is coupled to an input contact point and the shunt (Q ₂₇₎ forming the same voltage drop, and also having a resistance 57 and 51 made by measurement to have the same contacts around the location. Under strong automatic gain control conditions, (Q ₂₅ ) acts to further reduce the current at (Q ₂₇ ) and enhances the regulating function. Except for the current controlled by (Q ₂₅ ), (Q ₂₃ ) and ( The flow rate ratio between Q ₂₇ ) depends on their relative area ratio. The shape of (Q ₂₇ ) is adjusted to be 8 times that of (Q ₂₃ ). The current at Q ₂₇ is thus about 8 times that of the repeatability Q ₂₃ .

In the AM or FM scheme, the current applied to the route 18 flows through Q ₂₇ and is determined in accordance with the detected output and the mode. As noted earlier, the normal B + bias on lead 18 during AM operation is about 1.6 volts and 2.4 volts during FM operation.

The present invention may take other forms, but the design described above is particularly economical and therefore the overall cost is economical. Considering these performance requirements, the completion cost of the above-described AM-FM radio receiver using a single chip is less than the cost of not substantially integrating.

Claims (1)

As shown and described in detail herein, in the process of converting the intermediate frequency of the radio receiver selectively operated in the AM-mode and the FM-mode switch 32 into the audio frequency, the AM-FM detector 26 is used. Generates a DC signal component of AM-detection output or FM-detection output, and generates a first bias when the AM-mode is selected, and another second bias DC-type signal when the FM-mode is selected. And an AM-FM receiver comprising a control power supply 29 which causes the two bias signals and the direct current signal components to respond together to produce an output current of the main direct current component having a rating value as a function of these signals. Radio receiver.

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