JPH05284056A - Fm demodulator - Google Patents

Abstract

PURPOSE:To compensate the temperature characteristic of an entire gain and to enlarge the degree of freedom for designing a high frequency amplifier circuit, coil and transformer or the like by setting the temperature coefficient of the gain of a preintermediate frequency (IF) amplifier corresponding to the temperature coefficients of the gains of the high frequency amplifier in the preceding stage and a frequency mixer according to the resistance value of an external resistor. CONSTITUTION:IF signals are inputted from an input terminal 21 to an IF amplifier 6 provided with six operational pairs composed of transistors Q1-Q12 and two emitter followers composed of transistors Q22 and Q23 and after performing voltage amplification and amplitude limiting, audio signals are demodulated by an FM demodulation circuit 7 and outputted to a demodulated output terminal 25. Since the collector currents of the transistors Q13-Q18 are controlled corresponding to the temperature, the temperature coefficient of the voltage gain of the IF amplifier 6 is decided. This is performed by controlling the potentials of the common base lines of the transistors Q13-Q18 while using a temperature coefficient control circuit 16 and an external resistor REXT.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM demodulator used in an FM radio integrated circuit.

[0002]

2. Description of the Related Art In the case of constructing an FM radio receiver, FIG.
, A front-end integrated circuit 14 including a frequency mixer (MI) 2, a local oscillator (LO) 3, and a pre-FM amplifier (PIA) 4, and an intermediate frequency amplifier (I
It is generally composed of two integrated circuits of A) 6, an FM demodulator (FD) 7, and an FM demodulation integrated circuit 15 including a multiplex demodulator (MD) 8. In this figure, 1 is a high frequency amplifier (HA), 5 is a band pass filter (BF), 9 and 10 are power amplifiers (PA),
Reference numerals 11 and 12 are speakers, and 13 is an antenna.

On the other hand, as a general required performance of the FM receiver, the fluctuation of the receiving sensitivity with respect to the temperature change is small. That is, it is desired that the temperature coefficient of the voltage gain from the input of the antenna 13 to the FM demodulator 8 is ± 0.

[0004]

In the above-mentioned conventional FM demodulation integrated circuit, the temperature coefficient of the voltage gain of the intermediate frequency amplifier 6 included therein is fixed at about ± 0.
Therefore, it is necessary to design the temperature coefficient of the entire voltage gain of the front-end integrated circuit 14 and the high-frequency amplifier 1 to be 0, which causes a drawback that the selection of the front-end integrated circuit 14 and the design condition of the high-frequency amplifier 1 are restricted. there were.
That is, it is extremely limited to design the impedance of the load of the high-frequency amplifier (generally a coil, a transformer, etc.) and the transconductance temperature coefficient of the transistor used to be 0, or to design the mutual temperature coefficients in a complementary relationship. It was possible under the conditions, and it was difficult because it was a trade-off with other performance.

The object of the present invention is to eliminate such drawbacks, thereby expanding the selection of the front end integrated circuit and the allowable range of the temperature coefficient of the high frequency amplifier, and easily setting the temperature coefficient of the total gain to a desired value. It is to provide an FM demodulation device that can be set to a value (for example, 0).

[0006]

The structure of the present invention comprises an intermediate frequency amplifier having at least one differential pair for amplifying an input intermediate frequency signal to limit the amplitude, and an output signal of the intermediate frequency amplifier. An FM demodulator including an FM demodulator for demodulating an audio signal, means for controlling an operating current of the intermediate frequency amplifier so as to be proportional to a predetermined reference value,
And a temperature coefficient setting circuit including means for determining the temperature coefficient of the reference value according to the value of the external resistance.

Further, in the present invention, the temperature coefficient setting circuit includes two voltage sources having temperature coefficients having opposite polarities.
A base voltage supply circuit that supplies the base voltage of the transistors for the two voltage sources and a ratio adjustment circuit that changes the predetermined ratio by an external resistance value can be included.

[0008]

The temperature coefficient setting circuit in the present invention is, for example,
The outputs of two voltage sources having opposite temperature coefficients of polarities are added at a predetermined ratio determined by the external resistance value, and the added reference voltage is used for the constant current source that constitutes the differential pair of the intermediate frequency amplifier. It is supplied as the base voltage of the transistor. As a result, the operating current of the intermediate frequency amplifier changes in proportion to the given reference voltage.

Since the gain of the pre-intermediate frequency amplifier or the inter-frequency amplifier is proportional to the operating current, the gain of the pre-intermediate frequency amplifier or the inter-frequency amplifier is changed by changing the predetermined ratio by changing the external resistance value. It is possible to adjust the temperature coefficient of.

[0010]

FIG. 1 is a block diagram showing an FM radio receiver to which an embodiment of the present invention is applied, which corresponds to the conventional example of FIG. FIG. 2 is a circuit diagram showing a main part of FIG. 1, and shows an example of a main part of the FM demodulation integrated circuit 15a of FIG.

According to FIG. 1, in the present embodiment, an intermediate frequency amplifier (IA) 6 having at least one differential pair for amplifying an input intermediate frequency signal and limiting the amplitude, and an output of the intermediate frequency amplifier 6. FM demodulator (F
In the FM demodulation integrated circuit 15a including the D) 7 and the multiplex demodulator (MD) 8, the operating current of the intermediate frequency amplifier 6, which is a feature of the present invention, is controlled so as to be proportional to a predetermined reference value. Temperature coefficient setting circuit (TC) including means and means for determining the temperature coefficient of the reference value by the resistance value of the external resistor R _EXT connected to the temperature coefficient setting terminal 27.
C) 16 is provided.

According to FIG. 2, the intermediate frequency amplifier 6 has an NP
It includes the N-type transistors Q ₁ ~Q ₂₃ a resistor R ₁ to R _23, the temperature coefficient setting circuit 16, transistor Q ₂₅ which constitute the two voltage sources having opposite temperature coefficient polarity ~Q
₃₉ , Q ₅₀ , resistors R _{25 to} R _35, and a capacitor C ₁ , and
A transistor Q for a constant current source that forms the differential pair of the intermediate frequency amplifier 6 by adding the outputs of these two voltage sources at a predetermined ratio.
₁₃ transistors Q ₄₀ to Q ₄₇ constituting the base voltage supply circuit for supplying a base voltage of _{~Q 18, Q 51, Q 52} , Q
₂₉ , resistors R _{36 to} R ₄₁ , R ₂₉ , and operational amplifier A
₁ and transistors Q ₄₈ , Q ₄₉ and a constant voltage source (REG) 17 that form a ratio adjusting circuit that varies the predetermined ratio by the resistance value of the external resistor R _EXT .

In FIG. 2, R _IN is the input resistance and C _IN
And C _NF are capacitors for bypass.

Next, the operation of this embodiment will be described.
The following symbols will be used in the description.

A _En Transistor grounded voltage gain (n is transistor number) G _V Intermediate frequency amplifier differential gain per stage G _VIF Intermediate frequency amplifier gain I _cn Collector current (n is transistor number) R _m resistance value (m is resistance number) R _EXT External resistance R _EXT resistance value V _Bn Base voltage (n is transistor number) V _Rn Base-emitter voltage (n is transistor number) V _Rm Resistance Potential difference between both ends (m is resistance number) T Absolute temperature k Boltzmann constant q Electron charge h _FE transistor grounded emitter current amplification factor.

An IF signal is input from an input terminal 21 to an intermediate frequency amplifier 6 including six differential pairs of transistors Q _{1 to} Q ₁₂ and two emitter followers composed of transistors Q ₂₂ and Q ₂₃ , and voltage amplification and amplitude are applied. After the limitation is performed, the FM demodulation circuit 7 demodulates the audio signal and outputs it to the demodulation output terminal 25.

Here, the voltage gain of each differential pair is proportional to the current value of the constant current source composed of the transistors Q _{13 to} Q ₁₈ and the resistors R _{14 to} R _19, and the first stage is an example. The voltage gain G _V per unit is given by the following equation (1).

[0018]

The gain G _VIF as the intermediate frequency amplifier 6 is
Since it has a six-stage configuration, it is given by the following equation (2).

G _VIF = G _V ⁶ (2) In this embodiment, the temperature coefficient of the voltage gain of the intermediate frequency amplifier 6 is determined by controlling the collector currents of the transistors Q _{13 to} Q ₁₈ according to the temperature. and is, this is done by controlling the transistor Q ₁₃ common baseline potential external resistance and temperature coefficient control circuit 16 of R _EXT in to Q _18. Hereinafter, this operation will be described. The transistors Q _{25 to} Q ₃₄ and the resistors R _{25 to} R _{31 form} a Widlar type bandgap regulator, and the voltages represented by the following formulas (3) and (4) are respectively applied to the bases of the transistors Q ₄₄ and Q _45. Supply.

[0021]

Transistors Q44 and Q45 form a constant current source together with resistors R39 and R40, and their currents are given by the following equations (5) and (6), respectively.

[0023]

Next, the differential pair consisting of the transistors Q _{40 to} Q ₄₃ synthesizes I _C44 of the equation (5) and I _{C45 of the} equation (6) to form transistors Q ₄₆ , Q ₄₇ , Q ₅₁ and supplying a current I _C47 to the resistor R41 via the current mirror consisting of Q _52, synthesis ratio, transistors Q _40, Q _41, Q ₄₂ and Q
Determined by the base potential difference ΔV _BE of each differential pair of ₄₃ , the potential V _R41 of the resistor R ₄₁ is obtained as follows. The current I _C47 is given by the following equation (7).

[0025]

Here, ΔV _BE is the emitter potential difference between the transistors Q ₄₈ and Q ₄₉ and is given by the following equation (8).

[0027]

Since V _R41 = I _C47 × R ₄₁ ,
The following expression (9) is obtained, and this expression (9) and expressions (6) and (7)
Equation (10) is obtained from and.

[0029]

Next, the potential V _R41 of the resistor R ₄₁ is input to the operational amplifier A _1, the output of the operational amplifier A _1, i.e., the collector current of the transistor Q ₁₃ to Q _18, namely, of each differential pair Taking the first stage as an example, the operating current is given by the following equation (11).

I _C13 = (V _R41 + V _BE24 −V _BE13 ) / R ₁₄ ≈V _R41 / R ₁₄ (11) Therefore, the voltage gain G per one stage of the intermediate frequency amplifier 6
_V is given by the following equation (12) from the equations (1), (10) and (11).

[0032]

Next, the temperature coefficient of the voltage gain G _V .delta.G _V
Obtaining / δ _{T is} given by the following equation (13).

[0034]

If R ₃₉ = R ₄₀ = R ₄₁ is set in the equation (13), δV _BE / δT is generally a value of −2 mV / ° C., so that the relation of the equation (14) is obtained.

[0036]

Now, as a concrete numerical value, δV _BE / δT =
-2 mV / ° C, V _BE = 0.7V, (R ₁ + R ₂ ) / R ₁₄
= When _{1/6, R 42/10} <δG V / δT in the range of R _EXT <10R ₄₂ is + value of 0.55~-0.55% / ℃ is obtained, as the temperature coefficient of the intermediate frequency amplifier Total Is
Since the intermediate frequency amplifier 6 has a six-stage configuration, +3.3 to −
3.3% / ° C is obtained.

As described above, the gain temperature coefficient of the intermediate frequency amplifier can be arbitrarily set by the resistance value of the external resistor R _EXT . Further, from the formula (9), I at the reference temperature
_{If C44} = I _C45 is set, even if the external resistance R _EXT is changed, the gain of the intermediate frequency amplifier at the reference temperature does not change, and only the temperature coefficient can be set independently.

The value obtained in this example is -3.3 to + 3.3%.
Within the setting range of / ° C, it is possible to sufficiently compensate for the temperature coefficient (about ± 2% / ° C) of a general front end integrated circuit.

FIG. 3 shows an F to which the second embodiment of the present invention is applied.
FIG. 4 is a block diagram showing an M radio receiver, and FIG. 4 is a circuit diagram showing a main part of FIG. 3, showing an example of a main part of the FM integrated circuit 14a of FIG.

This embodiment comprises a local oscillator (RO) 3, a frequency mixing circuit (MI) 2, a pre-intermediate frequency amplifier (PIA) 4a including at least one differential pair, and a frequency mixer ( In the FM front-end integrated circuit 14a configured to amplify and output a predetermined intermediate frequency signal which is the output of MI) 2 by the pre-intermediate frequency signal amplifier (PIA) 4a, the operating current of the pre-intermediate frequency amplifier 4a. To control the temperature coefficient of the reference value to be proportional to a predetermined reference value, and an external resistor R connected to the temperature coefficient setting terminal 27.
A temperature coefficient setting circuit (TCC) 16 including means for determining the resistance value of _EXT is provided.

According to FIG. 4, the pre-intermediate frequency amplifier 4a
Includes NPN type transistors Q _{51 to} Q ₅₇ , Q _{61 to} Q ₆₄ and resistors R _{51 to} R ₅₆ , R _{62 to} R ₆₈ , and the temperature coefficient setting circuit 16 has two temperature coefficients having polarities opposite to each other. Transistors Q _{25 to} Q ₃₉ , Q ₅₀ and resistor R ₂₅ to constitute a voltage source
R ₃₅ and capacitor C 1 and the outputs of these two voltage sources are added at a predetermined ratio and supplied as the base voltage of transistors Q _{61 to} Q ₆₃ for the constant current source forming the differential pair of the pre-intermediate frequency amplifier 4 a. transistor _{Q 40 ~Q 47, Q 51,} Q 52, Q 29 constituting the base voltage supply circuit for the resistance R ₃₆ ~
R ₄₁ , R _29, operational amplifier A _1, and transistors Q ₄₈ , Q ₄₉ and a constant voltage source (RE) forming a ratio adjusting circuit for varying the predetermined ratio by the resistance value of the external resistor R _EXT.
G) 17 is included. Note that C _IN is a bypass capacitor.

[0043] and three differential pairs of the transistors Q ₅₁ to Q _56, the置中between frequency amplifier 4a before including emitter followers composed of the transistors Q _57, IF signal from the input terminal 21 via a frequency mixing circuit (MI) 2 is input Then, the voltage is amplified and output to the signal output terminal 28.

Here, the voltage gain of each differential pair is proportional to the current value of the constant current source consisting of the transistors Q _{61 to} Q ₆₃ and the resistors R _{64 to} R _66, and taking the first stage as an example. The voltage gain G _V per stage is given by the following equation (1).

[0045]

Gain G as preintermediate frequency amplifier 4a
_{Since VIF} has a three-stage configuration, it is given by the following equation (16).

G _VIF = G _V ³ (16) In the present embodiment, the temperature coefficient of the voltage gain of the pre-intermediate frequency amplifier 4a is controlled by controlling the collector currents of the transistors Q _{61 to} Q ₆₃ according to the temperature. This is performed by controlling the potential of the common baseline of the transistors Q _{61 to} Q ₆₅ by the temperature coefficient control circuit 16 and the external resistor REXT.

The operation of the temperature coefficient control circuit 16 is as follows.
It is similar to the embodiment of. The output of the operational amplifier A ₁ of the temperature coefficient control circuit 16, that is, the transistors Q _{61 to} Q
The base voltage of ₆₃ is V _R41 + V _BE24 . Further, the collector currents of the transistors Q _{61 to} Q ₆₃ , that is, the operating currents of the respective differential pairs are expressed by the above formula (1) taking the first stage as an example.
It is given as in 1). Therefore, the voltage gain G _V per one stage of the pre-intermediate frequency amplifier 4a is calculated by the above equation (12).
Given in.

The temperature coefficient of this voltage gain G _V δG _V / δT
Is also given by the above equation (13). If R ₃₉ = R ₄₀ = R ₄₁ is set in this equation (13), δV _BE / δT is generally a value of −2 mV / ° C., so that the above equation (14)
Can be obtained. Further, if also the same as in the first embodiment specific values, the value of _{R 42/10 <δG V /} δT in the range of R _EXT <10R ₄₂ is + 0.55~-0.55% / ℃ was obtained The total temperature coefficient of the intermediate frequency amplifier is +1.65 because the front intermediate frequency amplifier 4a has a three-stage configuration.
~ -1.65% / ° C is obtained.

As described above, the gain temperature coefficient of the intermediate frequency amplifier can be arbitrarily set by the resistance value of the external resistor R _EXT . Further, from the formula (9), I at the reference temperature
_{If C44} = I _C45 is set, even if the external resistance R _EXT is changed, the gain of the intermediate frequency amplifier at the reference temperature does not change, and only the temperature coefficient can be set independently.

-1.65 to +1.6 obtained in this example.
Within the setting range of 5% / ° C., it is possible to sufficiently compensate the temperature coefficient of a general high frequency amplifier circuit and the temperature coefficient of a frequency mixing circuit.

[0052]

As described above, according to the present invention, the temperature coefficient of the gain of the pre-intermediate frequency amplifier can be arbitrarily set by the resistance value of the external resistor. Therefore, the high frequency amplifier and the frequency mixer in the preceding stage can be set. The temperature characteristic of the overall gain can be compensated by setting it according to the temperature coefficient of the gain.
Therefore, there is an effect that the degree of freedom in designing the high frequency amplifier circuit, the coil, the transformer and the like can be expanded.

[Brief description of drawings]

FIG. 1 is a block diagram showing an FM radio receiver according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a main part of the embodiment shown in FIG.

FIG. 3 is a block diagram of a second embodiment of the present invention.

FIG. 4 is a circuit diagram showing a main part of the embodiment of FIG.

FIG. 5 is a block configuration diagram showing an FM radio receiver according to a conventional example.

[Explanation of symbols]

1 high frequency amplifier (HA) 2 frequency mixer (MI) 3 local oscillator (RO) 4, 4a pre-intermediate frequency amplifier (PIA) 5 band pass filter (BF) 6, 6a intermediate frequency amplifier (IA) 7 FM demodulator (FD) 8 Multiplex demodulator (MD) 9, 10 Power amplifier (PA) 11, 12 Speaker 13 Antenna 14, 14a Front end integrated circuit 15, 15a FM demodulation integrated circuit 16 Temperature coefficient setting circuit (TCC) 17 Constant voltage source (REG) 21 Input terminal 22 Bypass terminal 24 Power supply terminal 25 Demodulation output terminal 26 Grounding terminal 27 Temperature coefficient setting terminal 28 Output terminal A ₁ Operational amplifier C _IN , C _NF capacitors Q _{1 to} Q ₆₄ (NPN type) Transistor R _{1 to} R ₆₈ resistance R _IN input resistance R _EXT external resistance

Claims (3)

[Claims] 1. An intermediate frequency amplifier having at least one differential pair for amplifying an input intermediate frequency signal to limit the amplitude, and an FM demodulator for demodulating an audio signal from an output signal of the intermediate frequency amplifier. In an FM demodulator provided, a temperature coefficient including means for controlling an operating current of the intermediate frequency amplifier so as to be proportional to a predetermined reference value, and means for determining a temperature coefficient of the reference value by a value of an external resistor. An FM demodulator having a setting circuit. 2. A frequency mixing circuit for mixing a high frequency input signal with a signal from a local oscillator circuit to convert it into a predetermined intermediate frequency signal, and an intermediate frequency signal of the frequency mixing circuit for amplifying and at least one differential pair. With a pre-intermediate frequency amplifier circuit,
In an FM demodulator for demodulating a voice signal from the pre-intermediate frequency signal, means for controlling the operating current of the pre-intermediate frequency amplifier so as to be proportional to a predetermined reference value, and an external temperature coefficient of the reference value. An FM having a temperature coefficient setting circuit including means for determining the resistance value.
Demodulator. 3. The temperature coefficient setting circuit adds two voltage sources having temperature coefficients whose polarities are opposite to each other and outputs of the two voltage sources at a predetermined ratio to add the intermediate frequency amplifier or the pre-intermediate frequency amplifier. 3. A base voltage supply circuit for supplying as a base voltage of a transistor for a constant current source forming a differential pair of the above, and a ratio adjusting circuit for changing the predetermined ratio by an external resistance value. The FM demodulator according to item 1.