JPH0439245B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a receiver, and particularly to a receiver.
It is suitable for use in FM receivers.

[Background technology]

FIG. 1 is a circuit diagram of a main part of an FM receiver studied by the present inventor prior to the invention of the present application. 1 is a receiving antenna, and the received radio wave f _i is supplied to a high frequency amplification circuit 2 . The high frequency amplifier circuit 2 selects a broadcast radio wave of a desired frequency by a tuning operation of a tuning circuit (not shown), and obtains an output signal f ₀ . The output signal f ₀ is supplied to the base of a transistor Q ₁ forming part of the mixing circuit 3 .

Transistors Q ₁ and Q ₂ constitute a first differential amplifier, and a reference voltage V _ref1 is supplied to their bases via resistors R ₁ and R ₂ . Flows through transistors Q ₁ and Q ₂ depending on the voltage level of output signal f ₀
The amount of current of I _c1 and I _c2 is controlled. Note that a current _I0 , which is the sum of the currents _Ic1 and _Ic2 , flows through the constant current circuit _CS1 .
That is, the output signal f ₀ is transmitted through the transistors Q ₁ and Q ₂
is converted into a current change by

Transistors Q ₃ and Q ₄ forming a second differential amplifier are connected to the collector of the transistor Q ₁ . Furthermore, a transistor constituting the third differential amplifier is connected to the collector of transistor _Q2 .
Q ₅ and Q ₆ are connected. In addition, the resistances R ₃ and R ₄
adjusts the dynamic range of the first differential amplifier, and resistors R ₅ and R ₆ adjust the dynamic range of the second differential amplifier. And the transistor
The bases of Q ₄ and Q ₅ are connected to the reference voltage via resistor R ₇ .
A voltage that is the sum of V _ref1 and V _ref2 is supplied.

The bases of the transistors Q ₃ and Q ₆ are supplied with a voltage that is the sum of the reference voltages V _ref1 and V _ref2 via a resistor R ₈ , and superimposed thereon is supplied with a local oscillation frequency signal f _L from the local oscillation circuit 4 . be done. The capacitor C ₁ and the coil L ₁ constitute a tank circuit, which operates as a common load for the first and second differential amplifiers. The current I _c3 flowing through the tank circuit is controlled by the current amounts of the currents I _c1 and I _c2 and the frequency of the frequency signal f _L .

Then, for example, the resonant frequency of the tank circuit is
Center frequency 10.7M by tuning to 10.7MHz
An intermediate frequency signal I _f of Hz is obtained. Intermediate frequency signal I _f
is supplied to the next stage intermediate frequency amplification circuit (not shown). Note that a detection circuit, a low frequency amplification circuit, and a speaker (all not shown) are provided after the intermediate frequency amplification circuit.

By the way, when the present inventors investigated the relationship between the high frequency amplifier circuit 2 and the mixing circuit 3 and the local oscillation circuit 4, it was found that the high frequency amplifier circuit 2 has the following defects.

That is, the base of each transistor Q ₁ to Q ₆
Capacitance is provided between the emitter and between the base and collector. Of these capacitances, the base-collector capacitance C ₁ of the transistor Q ₁ and the base-emitter capacitance C ₂ of the transistor Q ₃ are assumed to be C 1 . It was found that when the output signal f ₀ was supplied to the mixing circuit 3, this output signal f ₀ leaked into the local oscillation circuit 4 via the capacitors C ₁ and C ₂ (as indicated by the arrow in the figure). ). Since the local oscillation circuit 4 has a high impedance, studies by the present inventors have revealed that the oscillation operation becomes unstable due to the leakage of the output signal f ₀ . It has been revealed that when the local oscillation frequency signal f _L becomes unstable, fluctuations in the local oscillation frequency tend to occur due to this.

Furthermore, due to variations in the resistance values of the resistors R ₁ , R ₂ and R ₇ , R ₈ , the transistors Q ₁ , Q ₂ and Q ₄ , Q ₅ ,
Studies by the present inventors have also revealed that the base voltages (DC voltages) of Q ₃ and Q ₆ fluctuate, and this becomes a factor in the occurrence of DC offset, making spurious interference more likely to occur.

[Object of the Invention] An object of the present invention is to prevent the output signal of a high frequency amplifier circuit from leaking to a local oscillation circuit, and to prevent direct current between transistors connected to a differential pair forming a part of a mixing circuit. The object of the present invention is to provide a receiver with equalized bias.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Summary of the invention]

A brief summary of the invention disclosed in this application is as follows.

That is, at the front end of the receiver,
A low impedance circuit and a multi-stage DC amplifier circuit are provided between the local oscillation circuit and the mixing circuit, and the low impedance circuit prevents the output signal of the high frequency amplifier circuit from leaking into the local oscillation circuit via the mixing circuit. The object of the present invention is to stabilize the oscillation operation of the local oscillation circuit, and also to supply a bias voltage to the mixing circuit by the output of the DC amplifier circuit, thereby preventing the generation of DC offset voltage in the mixing circuit. It is something.

〔Example〕

Hereinafter, an embodiment of a receiver to which the present invention is applied will be described with reference to FIGS. 2 and 3. The embodiment described below is an example of application to an FM receiver.
FIG. 2 is a block diagram showing the circuit configuration of the front end, and FIG. 3 is a detailed circuit diagram thereof. In explaining the embodiments, common reference numerals are given to each circuit block to facilitate comparison between the two.

In Fig. 2, 11 is a receiving antenna, f _i is a received signal, and 12 is a high frequency amplification circuit (in the following,
(referred to as RF circuit). By the tuning operation of the RF circuit 12, the desired broadcast radio wave is selected and the output signal is
f ₀ is supplied to the mixing circuit 13 via the No. 1 terminal.

On the other hand, the local oscillation circuit 14 oscillates a local oscillation frequency signal (hereinafter referred to as a local signal) f _L having a frequency 10.7 MHz higher than the output signal f ₀ ,
It is supplied to the next stage buffer 15. This battle 1
5, an amplifier 16 to be described later, and an inverting amplifier 17.
is provided to prevent leakage of the output signal f ₀ to the local oscillation circuit 14 .

The output signal f _L ' of the buffer 15 is supplied to the positive phase input terminal (+) of the amplifier 16. Then, at the inverted output terminal of the amplifier 16, in other words, at point d shown in FIGS. 2 and 3, an output signal of V ₀ =-A ₁ ·f _L ' is obtained. In addition, the non-inverting output terminal of the amplifier 16,
In other words, at point g shown in Figures 2 and 3,
An output signal of V ₀ ′=A ₁ ·f _L ′ is obtained. Note that A ₁ in the output signals V ₀ and V ₀ ' is the amplification degree of the amplifier 16. The output signal V ₀ is supplied to the negative phase input terminal (-) of the inverting amplifier 17 via the resistor R ₁₁ , and the output signal V ₀ ' is supplied to the positive phase input terminal (+) of the inverting amplifier 17 via the resistor R ₁₂ . Supplied. Also, the output signal
V ₀ and V ₀ ' are respectively supplied to the second and third differential amplifiers forming part of the mixing circuit 13.
The details are shown in FIG.

In amplifier 17, resistor R ₁₁ and capacitor C ₁₁
constitutes a Miller integrator. The output signal V ₀ does not flow into the inverting amplifier 17, but instead flows through the capacitor.
It appears at point f via C ₁₁ . A resistor R ₁₃ and diodes D ₁ and D ₂ are DC-connected between the point f and the earth line, and rectify the output signal V ₀ appearing at the point f. Therefore, the output voltage V _put appearing at point f
is the DC component with the AC component attenuated. This output voltage V _put defines the bias voltage of the negative phase input terminal of the DC amplifier 16 .

While the above circuit operation is being performed, the RF circuit 1
2 output signal f ₀ , amplifier 16 output signal V ₀ ,
V ₀ ′ (that is, local signal f _L ) is connected to the mixing circuit 13
supplied to Then, from the mixing circuit 13, an intermediate frequency _signal If with a center frequency of 10.7 MHz is obtained. The intermediate frequency signal I _f is supplied to a subsequent intermediate frequency circuit (not shown).

What should be noted here is the mixing circuit 13, the amplifier 1
6, the capacitances C ₁₂ , C ₁₃ , C ₁₄ , as shown in FIG.
Despite the presence of C ₁₅ , leakage of the output signal f ₀ of the RF circuit to the local oscillation circuit 14 is prevented.

This circuit operation will be explained in further detail with reference to FIG.

In the mixing circuit 13, transistors Q ₁₁ ,
_Q12 constitutes a first differential amplifier (lower stage amplifier). Resistor R ₂₁ is a balance resistor, and resistors R ₂₂ and R ₂₃ are emitter resistors. And transistor Q ₁₁ ,
The bias voltage of _Q12 is defined by the reference voltage _Vref11 supplied via resistors _R24 and _R25 .

Further, transistors Q ₁₃ and Q ₁₄ constitute a second differential amplifier, and transistors Q ₁₅ and Q ₁₆ constitute a third differential amplifier (both are upper stage amplifiers). The capacitances shown by dotted lines between the bases and emitters of transistors Q ₁₃ , Q ₁₄ , Q ₁₅ , and Q ₁₆ correspond to capacitances C ₁₂ and C ₁₃ shown in FIG. 2.

In the DC amplifier 16, transistors Q ₁₇ ,
Q ₁₈ constitutes a differential amplifier. Transistor Q ₁₇ ,
The capacitance shown by the dotted line between the base and emitter of Q ₁₈ corresponds to the capacitances C ₁₄ and C ₁₅ shown in FIG. 2. Transistor _Q19 defines the current flowing through the differential amplifier with the base voltage _VBB . Resistance _R26 , _R27
is the load resistance and CS ₁₁ is the constant current circuit.

On the other hand, the inverting amplifier 17 includes a constant current circuit CS ₁₂ ,
It is composed of transistors Q ₂₁ and Q ₂₂ connected in a differential pair. When the DC amplifier 16 and the inverting amplifier 17 are supplied with the local signal f _L ,
Bias voltages of transistors Q ₁₃ to _{Q 16} constituting the second and third differential amplifiers are defined.

In other words, a coil is connected between the base and emitter of transistor Q ₂₃ via terminals 2 and 3.
L ₁₁ and capacitors C ₂₁ and C ₂₂ are connected, and these constitute the local oscillation circuit 14. Note that the emitter resistor _R23 is provided to positively feed back the signal appearing at the emitter to the base.

The local signal f _L is supplied to the base of the transistor Q ₂₄ that constitutes the emitter follower 15 .
The output signal f _L ' is obtained by the voltage drop across the emitter resistor R ₂₉ and is supplied to the base of the transistor Q ₁₇ , in other words, to the positive phase input terminal (+) of the DC amplifier 16. Currents I ₁₇ , which flow through transistors Q ₁₇ and Q ₁₈ due to the level change of output signal f _L
The amount of current in _I18 is controlled. Resistors R ₂₆ and R ₂₇ perform current-voltage conversion operation, but the voltage change is caused by transistors Q ₂₁ and Q ₂₂ , as well as resistor R ₁₃ and diode.
It is converted into _an output voltage V put by D ₁ and D ₂ .
That is, the base voltage of the transistor _Q18 becomes equal to the base voltage of the transistor _Q17 , or in other words, the emitter potential of the transistor _Q24 due to the two-stage DC negative feedback operation of the transistors Q17 _{to Q23 .}

Here, when looking at the collector voltages of transistors Q ₁₇ and Q ₁₈ , they are set to V _BB −R ₂₆ (R ₂₇ )·I ₁₇ (I ₁₈ ). This voltage is the output signal for the DC component.
f _L ′ (AC component) is superimposed, and the bias voltage and local signal f _L are applied to the transistors Q ₁₃ to Q ₁₆ .
and will be supplied. Therefore, the transistor
It is not necessary to particularly supply a bias voltage to _Q13 to _Q16 , and the resistors _R7 and _R8 and the reference voltage _Vref2 described with reference to FIG. 1 are unnecessary. Also, no DC offset occurs between transistors _Q13 to _Q16 .

As described above, the output signal f ₀ of the RF circuit and the local signal f _L are supplied to the mixing circuit 13. At this time, the output signal f ₀ tends to leak into the local oscillator 14 via the capacitors C ₁₂ and C ₁₃ . However, the presence of the amplifier 16 prevents this leakage. Furthermore, an emitter follower 15 (transistor Q ₂₄ ), which has a high impedance when viewed from the output side, is provided between the local oscillation circuit ₁₄ and the amplifier ₁₆ .
The f ₀ component is also completely blocked here. In this way, leakage of the output signal f ₀ to the local oscillation circuit 14 is completely prevented.

Therefore, in the receiver having the circuit configuration described above, the oscillation operation of the local oscillation circuit 14 is not affected by the output signal f ₀ of the RF circuit 12, and an extremely stable local signal f _L can be obtained.

In addition, +V _CC power is supplied to terminal 4, and terminal 5
+V _CC power is supplied to the number terminal via the resonant coil _L12 . In the mixing circuit 13, transistors Q ₁₁ and Q ₁₂ are the transistors shown in FIG.
It operates in the same way as Q ₁ and Q ₂ . The transistors Q ₁₃ and Q ₁₄ operate in the same manner as the transistors Q ₃ and Q ₄ , and the transistors Q ₁₅ and Q ₁₆ operate in the same manner as the transistors Q ₅ and Q ₆ . The inductance of the coil L ₁₂ is set to a value that provides the maximum impedance for a frequency of 10.7 MHz. Therefore, depending on the polarity of the output signal f ₀ and the output signals V ₀ and V ₀ ′, when the transistors Q ₁₄ and Q ₁₆ are in the operating state, the output signal f ₀ and the output signal V ₀ have a center frequency of 10.7MHz. , V ₀ ′ are mixed, and the intermediate frequency signal I _f is
Obtained from the collectors of transistors Q ₁₄ and Q ₁₆ .
The intermediate frequency signal I _f is supplied to a subsequent intermediate frequency amplification circuit (not shown).

〔effect〕

(1) At the front end of the receiver, an emitter follower circuit is installed between the local oscillation circuit that oscillates the local signal and the mixing circuit to prevent the output signal of the high-frequency amplifier circuit from leaking from the mixing circuit to the local oscillation circuit. Thereby, the object of the present invention, which is to stabilize the oscillation operation of the local oscillation circuit, can be achieved.

(2) A DC amplifier and an inverting amplifier are provided together with the emitter follower circuit between the local oscillation circuit that oscillates the local signal and the mixing circuit, and an upper stage differential amplifier forms part of the mixing circuit based on the output signal of the DC amplifier. By supplying a bias voltage and a local signal to the upper stage differential amplifier, the effect of preventing the generation of DC offset voltage in the upper stage differential amplifier can be obtained.

Although the invention made by the present inventor has been specifically explained based on the embodiments above, the present invention is not limited to the above embodiments, and can be modified in various ways without departing from the gist thereof. It goes without saying that there is.

For example, the emitters of transistors Q ₁₁ and Q ₁₂ are
It may be grounded via a constant current circuit.
Further, the local oscillation circuit 14 may be replaced with an oscillation circuit including a voltage capacitance conversion element.

[Application field]

In the above explanation, the invention made by the present inventor will mainly be explained in the field of application that is the background thereof.
I explained the case where it is applied to an FM receiver, but
It is not limited to that.

For example, it can be applied to the front end of an AM receiver.

It can also be applied to a tuner section of a television receiver.

Furthermore, it can also be applied to communication devices, converters, etc. that use high frequency signals.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of the front end of a receiver that was considered prior to the invention of the present application, Figure 2 is a block diagram of the front end of an FM receiver showing an embodiment of the present invention, and Figure 3 is FIG. 2 is a circuit diagram showing a detailed circuit configuration of the front end of the FM receiver shown in FIG. 12...RF circuit, 13...mixing circuit, 14...
... Local oscillation circuit, 15 ... Emitter follower circuit, 16 ... DC amplifier, 17 ... Inverting amplifier,
Q ₁₁ , Q ₁₂ , Q ₁₃ , Q ₁₄ , Q ₁₅ , Q ₁₆ , Q ₁₇ , Q ₁₈ ,
Q ₁₉ , Q ₂₁ , Q ₂₂ , Q ₂₃ , Q ₂₄ ...transistor,
C ₁₂ , C ₁₃ , C ₁₄ , C ₁₅ ... Capacity, L ₁₁ , L ₁₂ ... Coil, C ₂₁ , C ₂₂ ... Capacitor, V _ref11 ... Reference voltage, f _i ... Received signal, f ₀ ... Output signal (high frequency signal), f _L , f _L ′ ... Local signal, V ₀ , V ₀ ' ... Output signal.

Claims (1)

[Claims] 1. Supplying the output signal of the high frequency amplifier circuit to one differential amplifier circuit of the differential type mixing circuit, and supplying the output signal of the local oscillation circuit to the first differential amplifier via the low output impedance circuit. circuit, and directly inputs both output signals of the first differential amplifier circuit to both inputs of the other differential amplifier circuit of the differential mixing circuit, and the first differential amplifier circuit By supplying both outputs to both inputs of a second differential amplifier circuit, and negative DC feedback of the output of the second differential amplifier circuit to the input of the first differential amplifier circuit, the mixing A receiver characterized in that the DC offset of the circuit is reduced and the output signal of the high frequency amplifier circuit is prevented from leaking into the local oscillation circuit.