JP2956719B2 - One-chip IC for radio receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a radio receiver.
It relates to a chip IC.

[0002]

2. Description of the Related Art As the number of terminal pins in an IC increases, the cost of the IC increases. Also, when the number of terminal pins is large, the number of external components is also large, but in such a state, the layout of the wiring pattern of the printed circuit board on which the IC and the external components are mounted becomes complicated, and The overall cost, including external components, will increase.

Further, when the number of terminal pins is large, the size of the IC package cannot be reduced, and the increase in external components hinders the miniaturization of the device. In addition, when the number of terminal pins is large, troubles such as a solder bridge are likely to occur at the time of mounting the IC, which also leads to an increase in cost.

Therefore, an increase in the number of terminal pins of an IC is
This is a major disadvantage for devices using C and its IC.

[0005]

The radio receiver is generally of the superheterodyne type and requires an intermediate frequency filter. The intermediate frequency filter is composed of a ceramic filter or the like. Therefore, when the radio receiver is formed into a one-chip IC, the intermediate frequency filter is externally attached to the IC, and therefore, the number of terminal pins of the IC increases by two. When the number of terminal pins increases, the above-described problem occurs.

Of course, if the receiver is of a straight type, an intermediate frequency filter is not required, and there is no need to externally attach the IC, so that the number of terminal pins of the IC can be reduced. However, in this case, since the selectivity is obtained only by the antenna tuning circuit, the interference characteristic is deteriorated and interference occurs.

The present invention provides a one-chip IC for a radio receiver which solves the above problems.

[0008]

Therefore, in the present invention, 1. The receiving system is a superheterodyne system. 2. The intermediate frequency filter is composed of a filter having a capacitor, a resistor and an amplifier, and is built in the IC. 3. The intermediate frequency is a frequency that is sufficiently lower than the general intermediate frequency of 450 to 455 kHz or the receiving band 531 to 1611 kHz, for example, 55 kHz. 4. Provide a circuit for removing the image signal. It is assumed that.

That is, when the reference numerals of the respective parts correspond to the embodiments described later, the first and second phases whose phases are different from each other by 90 °.
13 and 14 for forming local oscillation signals Soa and Sob
A first mixer circuit 12A to which a broadcast wave signal Sr and a first local oscillation signal Soa are supplied; and a broadcast wave signal Sr.
, A second mixer circuit 12B to which a second local oscillation signal Sob is supplied, and first and second mixer circuits 12A, 12A,
Operation circuit 16 to which 2B output signals Sia and Sib are supplied
A phase shift circuit 15 that shifts one signal of the signals Sia and Sib supplied from the first and second mixer circuits 12A and 12B to the arithmetic circuit 16 by 90 ° with respect to the other signal;
A bandpass filter 17 for extracting the intermediate frequency signal Si from the output signal of the arithmetic circuit 16, a detection circuit 22 for detecting the intermediate frequency signal Si extracted by the bandpass filter 17, and a detection output of the detection circuit 22 are supplied. And an amplifier 23 integrated into a one-chip IC 10, and at this time, the first and second local oscillation signals Soa, Sob
Is set such that the intermediate frequency fi of the intermediate frequency signal Si is sufficiently lower than the reception band, and the arithmetic circuit 16 outputs the output signals of the first and second mixer circuits 12A and 12B. The addition or subtraction is performed with the polarity at which the image signal Sm included in Sia and Sib is canceled.

[0010]

[Function] Band pass filter 17 for intermediate frequency filter
Can be built in the IC 10 by using a capacitor, a resistor, and an amplifier, so that the number of terminal pins can be reduced by two. In addition, since the receiving system is a superheterodyne system, sufficient selectivity can be obtained, and interference characteristics such as interference are improved.

[0011]

In FIG. 1, a part surrounded by a dashed line is an IC 10 for an AM receiver which is made into a one-chip IC according to the present invention.
T1 to T8 are the terminal pins, pin T3 is the power supply terminal pin, and pin T4 is the ground terminal pin.

Further, components or circuits outside the chain line are externally attached components, 1 is an antenna tuning circuit, and 2 is a resonance circuit for local oscillation. The tuning circuit 1 comprises a bar antenna (antenna tuning coil) L1 and a variable capacitor (variable capacitor) VC1.
Is composed of a local oscillation coil L2 and a variable capacitor VC2 interlocked with the variable capacitor VC1.

SW is a power switch, BATT is a 3V battery for power supply, VR is a variable resistor for volume control, SP
Is a speaker.

Then, the antenna tuning circuit 1 selects and extracts a broadcast wave signal (AM wave signal) Sr having a frequency fr, that is, Sr = Er.sin.omega.rtt.omega.r = 2.pi.fr. In the following signal processing, only the relative amplitude and phase of each signal are related, so the initial phase of each signal is omitted in the above equation and the following description.

The signal Sr is supplied to the high frequency amplifier 11 through the pin T1 of the IC 10, and the signal Sr from the amplifier 11 is supplied to the first and second mixer circuits 12
A, 12B.

Further, the local oscillation circuit 13 has a terminal pin T
2, the resonance circuit 2 is connected to form a local oscillation signal So. In this case, the oscillation frequency of the oscillation signal So is 2fo, and 2fo = (fr + fi) × 2fi is an intermediate frequency, and fi = 55 kHz.

The oscillation signal So is output from the counter 1
4 and is divided into local oscillation signals Soa and Sob having a frequency of ２ and a phase different from each other by 90 °. That is, the frequency is divided into signals Soa and Sob of Soa = Eo.cos.omega.t Sob = Eo.sin.omega.o.t.omega.o = 2.pi.fo.

The signals Soa and Sob are supplied to mixer circuits 12A and 12B and multiplied by the signal Sr, respectively, and the following signals Sia and Sib are extracted from the mixer circuits 12A and 12B. That is, Sia = Sr · Soa = Er · sin ωr t · Eo · cos ωot = α ｛sin (ωr + ωo) t + sin (ωr−ωo) t｝ Sib = Sr · Sob = Er · sin ωrt · Eo · sin ωt = α ｛−cos (ωr + ωo) t + cos (ωr−ωo) t｝ ωr = 2πfr α = Er · Eo / 2 The signals Sia and Sib are extracted.

Then, as described later, these signals Si
Of the signals a and Sib, the signal component of the angular frequency (ωr−ωo) is used as the intermediate frequency signal, and the angular frequency (ωr + ωo)
Since the signal component of the above formula is eliminated, for simplicity, ignoring the signal component of the angular frequency (ωr + ωo) in the above equation, Sia = α · sin (ωr−ωo) t Sib = α · cos (ωr−ωo) t.

At this time, since the image signal Sm is Sm = Em · sin ωmt ωm = ωo + ωiωi = 2πfi, the broadcast signal Sr from the tuning circuit 1 includes the image signal Sm. Then, the signals Sia and Sib at this time are as follows: Sia = α · sin (ωr−ωo) t + β · sin (ωm−ωo) Sib = α · cos (ωr−ωo) t + β · cos (ωm−ωo) β = Em · Eo / 2. Further, since ωr <ωo <ωm, the above equation is given by: Sia = α · sin (ωr−ωo) t + β · sin (ωm−ωo) = − α · sin (ωo−ωr) t + β · sin (ωm −ωo) Sib = α · cos (ωr−ωo) t + β · cos (ωm−ωo) = α · cos (ωo−ωr) t + β · cos (ωm−ωo)

Then, these signals Sia and Sib are supplied to the phase shift circuit 15. The phase shift circuit 15 is composed of, for example, an active filter using a capacitor, a resistor, and an operational amplifier. In a band of 55 kHz ± 10 kHz, the phase difference between the two input signals Sia and Sib is 90 ° ± 1 °.
The phase shifts to the following relationship. Thus, the phase shift circuit 15
, The signal Sib is delayed by 90 ° with respect to the signal Sia, and Sia = −α · sin (ωo−ωr) t + β · sin (ωm−ωo) Sib = α · cos (ωo−ωr + 90 °) t + β · cos (ωm−ωo + 90 °) = α · sin (ωo−ωr) t + β · sin (ωm−ωo) These signals Sia and Sib are supplied to the subtraction circuit 16 to be subtracted. Si = Sib−Sia = αsin (ωo−ωr) t + βsin (ωm−ωo) − −αsin (ωo−ωr) t + βsin (ωm−ωo)｝ = 2αsin (ωo−ωr) ) The signal Si indicated by t is extracted.

Here, since ωo−ωr = 2π (fo−fr) = 2πfi, the signal Si is a target intermediate frequency signal. Even if the broadcast wave signal Sr from the tuning circuit 1 includes the image signal Sm, the signal component due to the image signal Sm is not included in the intermediate frequency signal Si because it is canceled.

Thus, the intermediate frequency signal Si (and the signal component of the angular frequency (ωr + ωo)) converted from the broadcast wave signal Sr is extracted from the subtraction circuit 16.

The intermediate frequency signal Si is supplied to a band-pass filter 17 for an intermediate frequency filter.
The band-pass filter 17 includes, for example, a capacitor,
It consists of a biquad-type active filter using a resistor and an operational amplifier, and its pass band is 55k.
Hz ± 3 kHz. Thus, the bandpass filter 1
At 7, the unnecessary signal components are removed and only the intermediate frequency signal Si is extracted.

Then, the extracted intermediate frequency signal S
i is supplied to an AM detection circuit 22 through an amplifier 21 to extract an audio signal Ss (and a DC component V22 having a level corresponding to the level of the intermediate frequency signal Si), and the audio signal Ss is converted to a differential input audio amplifier. 23
The signal Ss from the amplifier 23 is supplied to the pin T
8 and to the speaker SP through the capacitor C5.

Further, the signal Sib from the mixer circuit 12B
Is supplied to the AGC voltage forming circuit 18 to form an AGC voltage. The AGC voltage is supplied to the amplifier 11 as a gain control signal, and the AGC voltage is applied to the signals Sia and Sib.
Is performed. In this case, a capacitor C3 is connected to the forming circuit 18 through the pin T5, and a low-pass filter is formed by the capacitor C3 to extract a direct current component which becomes an AGC voltage. Further, this AGC voltage is supplied as a reference voltage to each operational amplifier constituting the phase shift circuit 15 and the band pass filter 17.

The detection output of the detection circuit 22 is AGC
The AGC voltage is supplied to the voltage forming circuit 24 to form the AGC voltage.
The AGC voltage is supplied to the amplifiers 11 and 21 as a gain control signal, and AGC is performed on the intermediate frequency signals Sia, Sib and Si.

In this case, a capacitor C4 is connected to the forming circuit 24 through the pin T6, and a low-pass filter is formed by the capacitor C4 to take out the DC voltage V22 from the detection output. A voltage is formed. Also, this DC voltage V22 is
The DC component V22 supplied to the differential input of the amplifier 23 and supplied from the detection circuit 22 to the amplifier 23 together with the audio signal Ss is equivalently canceled.

Further, a variable resistor VR is connected to the amplifier 23 through a pin T7, and the gain of the amplifier 23 is controlled according to the resistance value of the variable resistor VR.
The volume is adjusted by the variable resistor VR.

The capacitor C6 is for bypassing signal components other than the audio signal Ss.

[0031]

As described above, according to the present invention, a broadcast can be received. In this case, in particular, according to the present invention, the bandpass filter 17 for the intermediate frequency filter is replaced by an active filter having a capacitor and a resistor. With the configuration, the IC 10 can be built in the IC 10, and therefore, the number of terminal pins can be reduced by two. Further, as apparent from FIG. 1, the IC 10 only requires eight terminal pins T1 to T8.

In addition, since the receiving system is a superheterodyne system, sufficient selectivity can be obtained and interference characteristics such as interference can be improved.

Further, since the intermediate frequency fi is sufficiently lower than the general intermediate frequency and reception band, the IC
Band pass filter (intermediate frequency filter) 1
7 occupies a larger area per stage, but the number of stages for obtaining the required selectivity characteristics can be reduced.
The area occupied by the whole can be reduced, and the IC can be formed.

When the intermediate frequency fi is low, the image characteristics deteriorate, but since the image signals Sm are removed by the circuits 12A to 16, the image characteristics do not deteriorate.

Furthermore, since the phase shift circuit 15 and the band-pass filter 17 is constituted by an active filter, these circuits 15, 17 there is a limit to the signal level that can be handled, the AGC respect amplifier 11 The phase shift circuit 15 and the band-pass filter 17
Does not cause excessive input.

The detection circuit 22 supplies the amplifier 23 with:
The DC component V22 is also supplied together with the audio signal Ss, and the DC component V22 is also supplied to the other of the differential inputs of the amplifier 23. Only Ss has been supplied. Therefore, between the detection circuit 22 and the amplifier 23,
There is no need to provide a DC cut capacitor, and terminal pins for externally connecting such a capacitor to the IC 10 are not required.

[Brief description of the drawings]

FIG. 1 is a system diagram of an example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Antenna tuning circuit 2 Resonance circuit for local oscillation 10 1 chip IC 11 High frequency amplifier 12A First mixer circuit 12B Second mixer circuit 13 Local oscillation circuit 14 Counter 15 Phase shift circuit 16 Subtraction circuit 17 Band pass filter 18 AGC voltage Forming circuit 21 Amplifier 22 AM detection circuit 23 Audio amplifier 24 AGC voltage forming circuit SP Speaker SW Power switch T1 to T8 terminal pin VR Variable resistor BATT Battery

Continuation of front page (56) References JP-A-1-273432 (JP, A) JP-A-3-27625 (JP, A) JP-A-3-266530 (JP, A) (58) Fields investigated (Int) .Cl. ⁶ , DB name) H04B 1/16 H04B 1/10 H04B 1/26

Claims (2)

(57) [Claims] 1. A circuit for forming first and second local oscillation signals having phases different from each other by 90 °; a first mixer circuit to which a broadcast wave signal and the first local oscillation signal are supplied; A second mixer circuit to which the broadcast wave signal and the second local oscillation signal are supplied; and a phase shift circuit for shifting the output signal of the first mixer circuit by 90 °.
And the output signal of the phase shift circuit and the output of the second mixer circuit.
To the output signals of the first and second mixer circuits.
Do not add with the polarity that cancels the included image signal.
An arithmetic circuit for stone subtraction, a band-pass filter for extracting an intermediate frequency signal from the output signal of the arithmetic circuit, a detection circuit for detecting the intermediate frequency signal extracted by the band-pass filter, a detection output of the detection circuit Time to extract DC component
And the detection output of the detection circuit and the
And an amplifier that differentially amplifies the obtained DC component into a one-chip IC, and the local oscillation frequency of the first and second local oscillation signals is
The intermediate frequency signal 1 for been radio receiver set so that the intermediate frequency is sufficiently lower than the reception band of the chip I
C. (2)Of a given frequencyOscillation circuit that forms an oscillation signal
And a first frequency dividing the oscillation signal by 90 °
And a counter for forming a second local oscillation signalcircuitWhen,A broadcast wave signal and the first local oscillation signal are supplied to the second
One mixer circuit, Receiving the broadcast wave signal and the second local oscillation signal;
A second mixer circuit, A phase shift circuit for shifting the output signal of the first mixer circuit by 90 °
Road and The output signal of the phase shift circuit and the output of the second mixer circuit
And the signal And the output signal of the second mixer circuit
Do not add with the polarity that cancels the included image signal.
To subtract An arithmetic circuit;this Bar for extracting the intermediate frequency signal from the output signal of the arithmetic circuit
Filter and the bandpass filter.
A detection circuit for detecting the extracted intermediate frequency signal,A circuit for extracting a DC component from the detection output of this detection circuit
Road and The detection output of the detection circuit and the signal output by the formation circuit
Amplifier that differentially amplifies the above DC component And one
Local oscillation frequency of the first and second local oscillation signalsBut,
Intermediate frequency of the above intermediate frequency signalIs receivedSufficient compared to bandwidth
Set to be low 1 chip I for radio receiver
C.