JP3204270B2 - Tuner circuit and tuner IC - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tuner circuit for a receiver.

[0002]

2. Description of the Related Art A superheterodyne receiver requires an intermediate frequency filter to extract an intermediate frequency signal. This intermediate frequency filter is generally constituted by a ceramic filter or a crystal filter. Cannot be integrated with the above circuit.

Therefore, it has been considered that the intermediate frequency filter is constituted by an active filter and integrated with another circuit.

FIG. 5 shows a tuner circuit of such a receiver, that is, from a high-frequency stage to a detection stage.
In the figure, a portion 10 surrounded by a chain line is a one-chip IC, T
1 to T4 are the external terminal pins. In addition, components outside the chain line are externally attached components or circuits, 1 is an antenna tuning circuit, and 2 is a resonance circuit for local oscillation. The tuning circuit 1 is composed of a bar antenna and a variable condenser (antenna coil and variable capacitor), and the resonance circuit 2 is composed of a local oscillation coil and a variable condenser interlocked with the variable condenser of the tuning circuit 1.

Then, a broadcast wave signal (AM wave signal) Sr having a frequency fr is selected and taken out by the antenna tuning circuit 1, and this signal Sr is supplied to a high frequency amplifier 11 through a pin T1 of the IC 10, and this amplifier 11 Is supplied to the mixer circuit 12 for supply. Further, the resonance circuit 2 is connected to the local oscillation circuit 13 through the terminal pin T2 to form a local oscillation signal So having an intermediate frequency of fo = fr + fi fi, and this signal So is supplied to the mixer circuit 12. . Thus, in the mixer circuit 12, the broadcast wave signal Sr becomes the intermediate frequency signal Si having the frequency fi.
Is frequency-converted.

Then, the signal Si is supplied to a band-pass filter 14 for an intermediate frequency filter. In this example, the bandpass filter 14 is configured by a biquad-type active filter using three operational amplifiers 141 to 143 and a capacitor and a resistor for feedback. Thus, the bandpass filter 1
At 4, 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 16 through an amplifier 15, and an audio signal Ss is extracted. The audio signal Ss is supplied to a speaker through an audio amplifier (not shown).

In this case, the band-pass filter 14
Is composed of an active filter having operational amplifiers 141 to 143, so that there is a limit to the signal level that the bandpass filter 14 can handle.

Therefore, the signal Si from the mixer circuit 12
Is supplied to the AGC voltage forming circuit 21 to form an AGC voltage, and the AGC voltage is supplied to the amplifier 11 as a control signal to perform AGC. Is limited so as not to be excessive.

Further, since the operational amplifiers 141 to 143 require a reference voltage, a reference voltage forming circuit 22 is provided, and the operational amplifiers 141 to 143
Is supplied with a reference voltage V22.

Thus, according to the IC 10, the reception of the AM broadcast is realized by the one-chip IC.

[0012]

By the way, the aforementioned AG
In the C voltage forming circuit 21, the intermediate frequency signal Si from the mixer circuit 12 is amplitude-detected, and the detection output is smoothed to obtain a DC voltage V21, and this DC voltage V21 is used as an AGC voltage. In order to obtain a DC voltage V21 by smoothing the detection output, a capacitor having a capacitance of several μF is required.

For this reason, in the above-mentioned IC 10, the capacitor C1 is connected to the forming circuit 21 through the terminal pin T2, and the detection output is smoothed by this capacitor C1 to extract the DC voltage V21 which becomes the AGC voltage.

Therefore, this IC 10 requires the terminal pin T2 and the external connection of the capacitor C1.

On the other hand, in the band-pass filter 14,
When noise occurs, the S / N of the intermediate frequency signal Si decreases, and the sensitivity substantially decreases. Therefore, in the band-pass filter 14, the generation of noise must be suppressed as much as possible. In order not to increase the noise in the bandpass filter 14, the reference voltage V22 supplied thereto must be at a low noise level, and in order to make the reference voltage V22 low noise, the output impedance of the forming circuit 22 must be sufficient. Need to be lower.

For this reason, in the above-described IC 10, the capacitor C2 having a capacitance of several μF is connected to the forming circuit 22 through the terminal pin T4.

Therefore, in this IC 10, the terminal pin T4 is required, and the capacitor C2 must be externally provided.

However, generally, 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, if 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, the addition of the two terminal pins T2 and T4 in the IC 10 is a great disadvantage for the IC 10 and the receiver using the IC 10.

Therefore, as for the reference voltage forming circuit 22, for example, as shown in FIG. 6, there is a method of forming a reference voltage V22 by using a constant current circuit 221, a diode 222 and a resistor 223. That is, in this case, no capacitor is required, and therefore, the terminal pin T in FIG.
4 and external capacitor C2 are not required.

However, in the case of the forming circuit 22 shown in FIG.
Since noise is generated by the diode 222 and the resistor 223, to reduce the equivalent noise resistance to 1 kΩ or less,
When V22 = 1V, the constant current source 221 to the diode 22
It is necessary to supply a current of 1 mA or more to the device 2, and the current consumption increases.

The present invention is to solve the above problems.

[0024]

Therefore, according to the present invention, a broadcast wave signal selected by an antenna tuning circuit and a local oscillation signal from a local oscillation circuit are supplied to convert the broadcast wave signal into an intermediate frequency signal. A mixer circuit for converting the
An active filter configured in a band-pass filter format to extract the intermediate frequency signal from the output of the mixer circuit
, An amplifier for amplifying the intermediate frequency signal extracted by the active filter, a detection circuit for detecting the intermediate frequency signal output from the amplifier, and the mixer circuit
An amplitude detection circuit for detecting an output signal, a predetermined control signal
The broadcast wave signal supplied to the mixer circuit according to
Control circuit for controlling the level of the signal,
A capacitor for smoothing the detection output and extracting the DC voltage
And a support, the control signal to the DC voltage to the control circuit
Signal to the mixer circuit.
AGC is performed by controlling the level of the broadcast wave signal
Together, the above DC voltage constitutes the above active filter
The tuner circuit is configured to supply the operational amplifier as a reference voltage to the operational amplifier .

[0025]

The reference voltage is formed by the capacitor C1 for forming the AGC voltage, thereby eliminating the need for a capacitor for forming the reference voltage and reducing the number of external terminal pins of the IC.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIGS.
For example, the configuration is as follows. That is, the mixer circuit 1
2 is supplied to an amplitude detection circuit 211, and an output terminal of the detection circuit 211
The capacitor C1 is connected through the terminal pin T2. This capacitor C1 is for smoothing the detection output of the detection circuit 211. Therefore, a DC voltage V21 of a level corresponding to the level of the intermediate frequency signal Si is obtained from the capacitor C1. The DC voltage V21 is, for example, 800 to 900 mV, depending on the power supply voltage and the level of the received broadcast wave signal Sr.

The voltage V21 is applied to the voltage comparison circuit 2
12 is supplied to one input terminal of the resistor R21.
To the other input terminal of the voltage comparison circuit 212. A reference voltage Vr is also supplied to the other input terminal.

A variable attenuator 213 is connected to a signal line between the terminal pin T 1 and the input terminal of the amplifier 11, and the comparison output of the comparator 212 is supplied to the attenuator 2.
13 is supplied as the control signal.

Further, the band-pass filter 14 is constituted by an active filter having the operational amplifiers 141 to 143 as described above. In this example, the operational amplifier 141 is constituted as follows.

That is, the emitters of the transistors Q41 and Q42 are commonly connected to the collector of the transistor Q48 for a constant current source, and the emitters are connected to the power supply line of the IC 10 to form the differential amplifier 41. A current mirror circuit 42 having transistors Q43 and Q44 and having the ground line of the IC 10 as a reference potential point is connected to the collectors of the transistors Q41 and Q42.

Further, the collectors of the transistors Q41 and Q43 are connected to the collector of the transistor Q47 through the transistor Q45. The transistor Q47 and the transistors Q48 and Q49, together with the transistor Q46, constitute a current mirror circuit 43 using the power supply line as a reference potential point.
Is connected to a constant current source 44.

Then, the intermediate frequency signal Si from the mixer circuit 12 is supplied to the base of the transistor Q42 through a filter resistor R41, and the transistor Q42
A filter feedback resistor R42 and a capacitor C41 are connected between the collector of the transistor 45 and the base of the transistor Q42.

Further, the DC voltage V21 obtained at the capacitor C1 by the detection circuit 211 is supplied as a reference voltage to the base of the transistor Q41.

Further, the transistors Q51 and Q52 provide
The current mirror circuit 44 uses the ground line as a reference potential point.
The collector of the transistor Q51 on the input side is connected to the base of the transistor Q53, the emitter of the transistor Q53 is connected to the collector of the transistor Q49, and the collector of the transistor Q52 is connected to the base of the transistor Q41. You.

Each transistor is a transistor Q
The characteristics of the transistors Q48 and Q49 are the same except for the characteristics of the transistors Q48 and Q49. The junction area between the base and the emitter of the transistors Q48 and Q49 is twice and three times the junction area between the base and the emitter of the transistor Q46. Is the value I0, the collector current of the transistor Q48 is 2
The double value 2I0 and the collector current of the transistor Q49 are tripled 3I0.

Further, the operational amplifiers 142 and 143 have the same configuration as the operational amplifier 141.
The DC voltage V21 from the capacitor C1 is also supplied to the second and 143 as a reference voltage. However, the operational amplifier 142,
In 143, the transistor corresponding to the input side transistor Q46 of the current mirror circuit 43 is the operational amplifier 1
41 is also used by the input side transistor Q46 of the current mirror circuit 43.

According to such a configuration, the mixer circuit 12
Is detected by a detection circuit 211, and a DC voltage V21 having a level corresponding to the level of the intermediate frequency signal Si is obtained in a capacitor C1. And
This DC voltage V21 is compared with the reference voltage Vr in the voltage comparison circuit 212. When V21> Vr, the variable attenuation circuit 213 is controlled by the comparison output, and the level of the broadcast wave signal Sr supplied to the amplifier 11 decreases. Is done.

Therefore, AGC is performed on the broadcast wave signal Sr supplied to the amplifier 11, and the level of the intermediate frequency signal Si supplied from the mixer circuit 12 to the band-pass filter 14 is changed to the level of the band-pass filter. 1
4 is limited to a range that does not exceed the allowable input level.

Further, in this case, since the voltage V21 obtained at the capacitor C1 is supplied to the transistor Q41 as a reference voltage, the transistor Q41 and the transistor Q42 operate as the differential amplifier 41, and the differential amplifier 41 The current mirror circuit 42 and the transistors Q45 and Q47 operate as the operational amplifier 141. Further, the operational amplifiers 142 and 143 operate similarly.

Therefore, these operational amplifiers 141 to 141
43 and the filter elements R41, R41 connected thereto.
The circuit 14 operates as a band-pass filter by means of 42, C41, etc., and the intermediate frequency signal Si is taken out and the amplifier 1
5 is supplied.

In this case, since the collector current of the transistor Q48 is 2I0, the transistor Q41,
The emitter current of Q42 has a value I0. Although the collector current of the transistor Q49 has a value of 3I0, for simplicity, assuming that the value is I0 as shown in parentheses in FIG. 1, the emitter current of the transistor Q53 is also the value I0.
Therefore, when the emitter current of value I0 is applied to transistor Q53, the value of the base current of transistor Q53 is
If B, the base current of the transistor Q41 also becomes the value IB.

Then, the base current I of the transistor Q53
B is supplied to the transistor Q51 of the current mirror circuit 44, so that the collector of the transistor Q52 has the value I
The collector current of B will flow in. Therefore,
The base current IB of the transistor Q41 is
As a result, the transistor Q41
Does not flow through the capacitor C1. That is, the DC voltage V21, which is the AGC voltage, is charged and discharged in the capacitor C1, but the base current of the transistor Q41 does not affect the charging and discharging of the capacitor C1.

Since the collector current of the transistor Q49 is actually 3I0, the collector current of the transistor Q52 has a value of 3IB, so that not only the base current of the transistor Q41 of the operational amplifier 141 but also the operational amplifier 14
The base current of 2,143 similar transistors will also flow through transistor Q52.

Therefore, in addition to the transistor Q41 of the operational amplifier 141, the operational amplifier 142,
Even if similar transistors 143 are connected, the base current of those transistors does not charge or discharge the capacitor C1, so that an appropriate AGC is performed on the broadcast wave signal Sr supplied to the amplifier 11.

As described above, according to the present invention, when the band-pass filter 14 for the intermediate frequency filter is constituted by an active filter, the reference voltage of the operational amplifiers 141 to 143 constituting the active filter is set to AG.
Since the DC voltage V21 of the C voltage forming circuit 21 is used, the reference voltage forming circuit 22 in FIG.
Therefore, the terminal pin T4 of the IC 10 becomes unnecessary. Also, there is no need to connect the capacitor C2.

Further, the capacitor C 1 is connected to the operational amplifier 14.
Since the reference voltage sources of 1 to 143 are used, the output impedance is sufficiently low, and the reference voltage is sufficiently low noise.
Is not reduced.

As shown in FIG. 6, it is not necessary to supply a large current to reduce the output impedance of the voltage source of the reference voltage, so that the current consumption can be reduced.

In addition, since the AGC is performed by the AGC forming circuit 21 in the preceding stage of the band pass filter 14, the level of the intermediate frequency signal Si supplied to the band pass filter 14 is limited. Therefore, even if the allowable input level is limited, the intermediate frequency signal S
Non-linear distortion does not occur in i, and the receiving characteristics do not deteriorate.

Further, the DC voltage V21 of the capacitor C1 is
When the reference voltage is supplied to the operational amplifiers 141 to 143, the base current of the transistor Q41 of the operational amplifiers 141 to 143 is compensated by the transistors Q49 and Q51 to Q53, so that the DC voltage V21 of the capacitor C1 is
Even when the reference voltage is supplied to the operational amplifiers 141 to 143, the DC voltage V21 of the capacitor C1 does not fluctuate, and AGC on the broadcast wave signal Sr can be performed normally.

FIG. 3 shows a specific example of the detection circuit 211 and the voltage comparison circuit 212. That is, the intermediate frequency signal Si from the mixer circuit 12 is supplied to the base of the transistor Q11 in the opposite phase by the differential amplifier A11 and is supplied to the base of the transistor Q12 in the same phase by the differential amplifiers A11 and A12. Then, at this time, the transistor Q11,
Q12 is a differential amplifier A13 with respect to the transistor Q13.
And a predetermined reference voltage is supplied to the base of the transistor Q13.

Therefore, the transistor Q11 turns on every negative half cycle of the intermediate frequency signal Si, and the transistor Q12 turns on every positive half cycle of the intermediate frequency signal Si. As shown in FIG. 4, a signal current I13 obtained by full-wave rectifying the intermediate frequency signal Si is output.

The current I13 is supplied to the capacitor C1 through the current mirror circuits A14 and A15, so that the capacitor C1 has a DC voltage V21 of a level corresponding to the level of the intermediate frequency signal Si from the mixer circuit 12. can get.

Further, the DC voltage V of the capacitor C1
21 is supplied to a resistor R21 and also to a differential amplifier A21 for voltage comparison, and an output of the differential amplifier A21 is taken out as a control current of an AGC through a current mirror circuit A22.

The DC voltage V21 obtained at the capacitor C1 is supplied as a reference voltage to the differential amplifiers A11, A12, etc., and at this time, the base voltage flowing from the capacitor C1 to the differential amplifiers A11, A12, A21, etc. The current is compensated by the current mirror circuit A31.

[0055]

According to the present invention, when the band-pass filter 14 for the intermediate frequency filter is constituted by an active filter, the DC voltage of the AGC voltage forming circuit 21 is used as a reference voltage for the operational amplifiers 141 to 143 constituting the active filter. Since the voltage V21 is used, the reference voltage forming circuit 22 in FIG. 5 becomes unnecessary, and therefore, the terminal pin T4 of the IC 10 becomes unnecessary. Also, there is no need to connect the capacitor C2.

Further, the capacitor C 1 is connected to the operational amplifier 14.
Since the reference voltage sources of 1 to 143 are used, the output impedance is sufficiently low, and the reference voltage is sufficiently low noise.
Is not reduced.

As shown in FIG. 6, it is not necessary to supply a large current to reduce the output impedance of the voltage source of the reference voltage, so that the current consumption can be reduced.

Further, since the AGC is performed by the AGC forming circuit 21 in the preceding stage of the band pass filter 14, the level of the intermediate frequency signal Si supplied to the band pass filter 14 is limited. Therefore, even if the allowable input level is limited, the intermediate frequency signal S
Non-linear distortion does not occur in i, and the receiving characteristics do not deteriorate.

Further, the DC voltage V21 of the capacitor C1 is
When the reference voltage is supplied to the operational amplifiers 141 to 143, the base current of the transistor Q41 of the operational amplifiers 141 to 143 is compensated by the transistors Q49 and Q51 to Q53, so that the DC voltage V21 of the capacitor C1 is
Even when the reference voltage is supplied to the operational amplifiers 141 to 143, the DC voltage V21 of the capacitor C1 does not fluctuate, and AGC on the broadcast wave signal Sr can be performed normally.

[Brief description of the drawings]

FIG. 1 is a connection diagram showing a part of an example of the present invention.

FIG. 2 is a connection diagram showing a continuation of FIG. 1;

FIG. 3 is a connection diagram of one example of the present invention;

FIG. 4 is a waveform chart for explaining the operation of the circuit of FIG. 2;

FIG. 5 is a connection diagram of a conventional example.

FIG. 6 is a partial connection diagram of a conventional example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 antenna tuning circuit 2 resonance circuit 10 1-chip IC 11 high-frequency amplifier 12 mixer circuit 13 local oscillation circuit 14 band-pass filter 15 amplifier 16 AM detection circuit 21 AGC voltage forming circuit 141 to 143 operational amplifier 211 amplitude detection circuit 212 voltage comparison circuit 213 variable Attenuation circuit T1 to T4 External terminal pin

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-78310 (JP, A) JP-A-2-162814 (JP, A) JP-A-61-145936 (JP, A) JP-A-62-1986 14530 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04B 1/18 H04B 1/26 H04B 1/06 H04B 1/16

Claims (2)

(57) [Claims] And 1. A broadcast wave signal selected by the antenna tuning circuit, a local oscillation signal is supplied the broadcast wave signal from a local oscillator and mixer circuit for converting the intermediate frequency signal, the band pass filter format An active filter configured to extract the intermediate frequency signal from the output of the mixer circuit
A capacitor, an amplifier for amplifying the intermediate frequency signal extracted by the active filter, a detection circuit for detecting the intermediate frequency signal output from the amplifier, an amplitude detection circuit for detecting an output signal of the mixer circuit, predetermined Supplied to the mixer circuit according to the control signal of
A control circuit for controlling the level of the broadcast wave signal, and a DC voltage obtained by smoothing the detection output of the amplitude detection circuit.
And a capacitor for issuing, supplying the DC voltage as the control signal to the control circuit
The broadcast supplied to the mixer circuit.
AGC is performed by controlling the level of the wave signal, and the DC voltage is applied to an operation constituting the active filter.
A tuner circuit that supplies the amplifier with its reference voltage . 2. A mixer circuit for receiving a broadcast wave signal selected by an antenna tuning circuit and a local oscillation signal from a local oscillation circuit to convert the broadcast wave signal into an intermediate frequency signal, and a band pass filter. An active filter configured to extract the intermediate frequency signal from the output of the mixer circuit
A capacitor, an amplifier for amplifying the intermediate frequency signal extracted by the active filter, a detection circuit for detecting the intermediate frequency signal output from the amplifier, an amplitude detection circuit for detecting an output signal of the mixer circuit, predetermined And a control circuit for controlling the level of the broadcast wave signal supplied to the mixer circuit in accordance with the control signal is integrated into a one-chip IC, and the detection output of the amplitude detection circuit is smoothed to extract a DC voltage Has an external terminal pin externally connected to the capacitor , and supplies the DC voltage to the control circuit as the control signal.
The broadcast supplied to the mixer circuit.
AGC is performed by controlling the level of the wave signal, and the DC voltage is applied to an operation constituting the active filter.
Amplifier, Ju so supplied as the reference voltage
IC.