JPH05275976A - Ic and tuning circuit using the same - Google Patents

Abstract

(57) [Summary] [Purpose] The variable capacitor of the tuning circuit is integrated into an IC. A phase inversion type variable gain amplifier 10, a capacitor C11 connected between an input terminal and an output terminal of the variable gain amplifier 10, and an external connection terminal T11 connected to the capacitor C11 are provided. With the variable gain amplifier 10, the capacitance of the capacitor C11 seen from the external connection terminal T11 is
It is assumed that the voltage gain of the variable gain amplifier 10 is almost doubled. When the coil L11 is connected to the external connection terminal T11, the tuning circuit 1 is constituted by the coil L11 and the capacitor C11. The tuning frequency of the tuning circuit 1 is changed by changing the voltage gain of the variable gain amplifier 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an IC and a tuning circuit using this IC.

[0002]

2. Description of the Related Art Various ICs as ICs for radio receivers
However, in a conventional monolithic IC for a radio receiver, an antenna tuning circuit for selecting a broadcast wave signal (received signal) is composed of an external bar antenna coil and a variable capacitor (variable capacitor). There is.
Further, the resonance circuit of the local oscillation circuit is also composed of an external local oscillation coil and a variable capacitor similarly.

[0003]

Therefore, even if the main part of the receiving circuit can be integrated into an IC, the effect of the IC becomes small if the above external parts are provided. Further, when the receiver is assembled, it is necessary to adjust the value of the coil or the variable capacitor for tracking adjustment.

The present invention is intended to solve such a problem.

[0005]

Therefore, in the present invention, when the reference numerals of the respective parts correspond to the embodiments described later, the phase inversion type variable gain amplifier 10 and the input end of the variable gain amplifier 10 are provided. A capacitor C11 connected to the output terminal and an external connection terminal T11 connected to the capacitor C11 are provided. Then, the capacitance of the capacitor C11 viewed from the external connection terminal T11 is set by the variable gain amplifier 10 to be approximately the voltage gain times AV of this variable gain amplifier 10, and when the coil L11 is connected to the external connection terminal T11, The tuning circuit 1 is constituted by the coil L11 and the capacitor C11, and the tuning frequency fo of the tuning circuit 1 is changed by changing the voltage gain AV of the variable gain amplifier 10.

[0006]

The apparent capacitance of the capacitor C11 is almost multiplied by the voltage gain AV by the variable gain amplifier 10. Therefore, the variable capacitor required for the tuning circuit 1 can be integrated into an IC. At this time, if the voltage gain AV of the variable gain amplifier 10 is changed, the apparent capacitance of the capacitor C11 changes, so that the tuning frequency can be changed.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, a circuit in a range indicated by a chain line is an IC.
And T11 and T12 are external connection terminals (pins). The bar antenna coil L11 for the antenna tuning circuit is externally attached to the terminals T11 and T12, and the terminal T
11 and T12 are connected to the bases of the transistors Q11 and Q21 and the bases of the transistors Q12 and Q22, respectively.

In this case, the transistors Q11, Q21, Q1
2, Q22, together with other transistors, form a phase inversion type variable gain amplifier 10. That is, the emitters of the transistors Q11 and Q12 are connected to a constant current source Q13 whose ground potential is the reference potential point to configure the differential amplifier 11, and the emitters of the transistors Q21 and Q22 are variable constant voltage sources whose ground potential is the reference potential point. The differential amplifier 21 is configured by being connected to the current source Q23. In addition, V12 is a base bias power supply.

Further, the collectors of the transistors Q11 and Q22 are connected to the collector of the transistor Q13. This transistor Q13 has this as the input side, and transistor Q13
The current mirror circuit 12 is configured with 14 as the output side and the power supply terminal T13 as the reference potential point. The collector of the transistor Q14 is connected to the collector of the transistor Q16.

The collectors of the transistors Q12 and Q21 are connected to the collector of the transistor Q23. This transistor Q23 has this as the input side, and transistor Q24
Is the output side, and the current mirror circuit 22 is configured with the power supply terminal T13 as the reference potential point. And
The collector of the transistor Q24 is connected to the collector of the transistor Q15.

Further, the transistors Q15 and Q16 constitute a current mirror circuit 13 with these as an input side and an output side and the ground being a reference potential point. Also,
The collectors of transistors Q14 and Q16 are load resistors R12
Through the power source V12. The transistor Q
Reference numeral 17 is for the base bias of the transistors Q15 and Q16.

As described above, in this example, the variable gain amplifier 10 is constructed.

Further, 30 denotes a buffer circuit. That is, with the transistors Q31, Q32 and the resistor R31,
The differential amplifier 31 is configured with the ground as the reference potential point, and the emitter-grounded transistor Q33 is provided.
Its base is connected to the collector of transistor Q32.
Its emitter is connected to the base of transistor Q32.

The collectors of the transistors Q14 and Q16 are connected to the base of the transistor Q31, and the emitter of the transistor Q33 is connected to the terminal T11 via the capacitor C11.
Connected to.

According to this structure, the power supply V12 base-biases the transistors Q11, Q12, Q21, and Q22. Further, since the signal current Vin is supplied to the bases of the transistors Q11, Q12, Q21, Q22 by the signal voltage Vin obtained at the coil L11, 2I13: constant current source Q13 output constant current 2I23: constant current source Q23 output constant. Currents I11, I12: collector currents of transistors Q11, Q12 I21, I22: collector currents of transistors Q21, Q22, I11 = I13-ΔI I12 = I13 + ΔI I21 = I23-aΔI I22 = I23 + aΔI ΔI: signal current component (AC Component) a: The ratio of the current I13 and the current I23.

The current (I11 + I22), which is the sum of the current I11 and the current I22, becomes the input current of the current mirror circuit 12. Therefore, if I14 is the collector current of the transistor Q14, then I14 = I11 + I22 = (I13-ΔI ) + (I23 + aΔI) = I13 + I23− (1-a) ΔI.

The current (I12 + I21), which is the sum of the current I12 and the current I21, becomes the input current of the current mirror circuit 22. Therefore, if I24 is the collector current of the transistor Q24, then I24 = I12 + I21 = (I13 + ΔI) + (I23-aΔI) = I13 + I23 + (1-a) ΔI.

Since this current I24 becomes an input current of the current mirror circuit 13, I16: I16 = I24 = I13 + I23 + (1-a) ΔI, where I16 is the collector current of the transistor Q16.

Iout is the current flowing through the resistor R12, and the current (I14-I) is the difference between the current I14 and the current I16.
16) flows through the resistor R12, Iout = I14-I16 = {I13 + I23- (1-a) ΔI}-{I13 + I23 + (1-a) ΔI} =-(1-a) ΔI- (1-a ) ΔI = -2 (1-a) ΔI (1)

In this case, the current Iout expressed by the equation (1) does not include the direct current component but only the signal current ΔI.
Therefore, the current Iout is the output signal current. Further, since the signal current Iout flows through the resistor R12, the output signal voltage Vout is obtained at the resistor R12.

At this time, if β is the current amplification factor of the transistors Q11, Q12, Q21, Q22, then ΔI = Iinβ, so that the equation (1) is Iout = -2 (1-a) ΔI = −2 (1-a) Iin · β (2) And the signal current Iin is the input signal current,
The current Iout flowing through the resistor R12 is the output signal current.

Therefore, according to the equation (2), the output signal current Iout has a reverse phase with respect to the input signal current Iin, and the amplifier 10 is a phase inverting amplifier. Further, since the input signal current Iin flows due to the signal voltage Vin from the coil L11 and the output signal current Iout flows through the resistor R12 to generate the signal voltage Vout at the resistor R12, the amplifier 10 is also a voltage amplifier.

Further, in the equation (2), since the value a changes according to the magnitude of the constant current 2I23 of the constant current source Q23, the amplifier 10 has a variable gain whose voltage gain changes according to the magnitude of the constant current 2I23. It is also an amplifier.

Further, in the circuit 30, since the output of the differential amplifier 31 is 100% negatively fed back by the transistor Q33, the circuit 30 functions as a buffer circuit having an in-phase and a single voltage gain.

Therefore, the circuit of FIG. 1 can be represented by the equivalent circuit of FIG.

In this equivalent circuit, -AV is the voltage gain of the amplifier 10, C10 is the capacitance when the capacitor C11 is viewed from the terminal T11, and C10 = (1 + AV) C11 ...・ It becomes (3).

That is, if i11 is the signal current flowing through the capacitor C11, then i11 = (Vin-Vout) .j.omega.C11 = {Vin-(-Vin.Av)}. J.omega.C11 = Vin (1 + AV) .j.omega.C11 = Vin.j.omega. Since (1 + AV) C11, the equation (3) holds.

Therefore, the antenna tuning circuit 1 is constituted by the coil L11 and the capacitor C10.

At this time, the capacitance C10 can be changed by the voltage gain AV, and the gain AV can be changed by the ratio a, that is, the magnitude of the constant current 2I23. Therefore, the tuning frequency of the tuning circuit 1 is constant. It can be changed by changing the magnitude of the constant current 2I23 of the current source Q23.

Therefore, it is possible to select and extract a broadcast wave signal of an arbitrary frequency from the tuning circuit 1.

The extracted signal is supplied to the high-frequency amplifier 2 and further, although not shown, is supplied to the mixer circuit and the local oscillation signal from the local oscillation circuit is supplied to the mixer circuit for tuning. The signal from the circuit 1 is frequency-converted into an intermediate frequency signal in the mixer circuit. The resonance circuit of the local oscillation circuit can also be configured similarly to the tuning circuit 1.

In this case, according to the present invention, when the tuning circuit 1 is constructed, the capacity of the capacitor C11 is equivalently (1 + AV) times, so that the capacity of the capacitor C11 itself can be reduced. .. Therefore, the capacitor C11 can be integrated into an IC together with other elements, so that it is not necessary to externally attach a tuning capacitor to the IC as in the conventional case. In addition, the variable capacitor of the resonance circuit of the local oscillator circuit 4 can also be integrated into an IC,
There is no need to attach it externally to the IC.

Further, productivity is improved because external parts that require adjustment are unnecessary. Further, since external parts are not required, variations in the performance of the receiver using this IC are reduced, and when the parts are laid out on the printed circuit board, there is almost no influence between the parts. Furthermore, the performance of the IC is almost the same as that of the receiver.

FIG. 3 shows a simulation example of the tuning characteristic of the tuning circuit 1 of FIG. 1. In this example, L11 = 200 μH C11 = 127 pF I13 = 100 μA / 2 I23 = 100 μA / 2 , When the tuning frequency fo is set to 1000 kHz. Further, in the case of this numerical example, when the current 2I23 is changed, when 2I23 = 80 μA, fo = 2082 kHz 2I23 = 90 μA 1275 kHz 2I23 = 100 μA 1000 kHz (the above value) 2I23 = 125 μA 714 kHz 2I23 = 150 μA 585 kHz 2I23 = 200 μA 454 kHz, which shows that the frequency band of AM broadcasting can be covered.

Thus, according to the present invention, the external component, that is, the variable capacitor can be eliminated.

[0036]

According to the present invention, when the tuning circuit 1 is constructed, the capacitance of the capacitor C11 is equivalently (1 + AV
), The capacitance of the capacitor C11 itself can be reduced. Therefore, the capacitor C11 can be integrated into an IC together with other elements, so that it is not necessary to externally attach a tuning capacitor to the IC as in the conventional case. Further, the variable capacitor of the resonance circuit of the local oscillation circuit 4 can also be integrated into an IC, and does not need to be externally attached to the IC.

Furthermore, since external parts that need to be adjusted are not required, productivity is improved. Further, since external parts are not required, variations in the performance of the receiver using this IC are reduced, and when the parts are laid out on the printed circuit board, there is almost no influence between the parts. Furthermore, the performance of the IC is almost the same as that of the receiver.

[Brief description of drawings]

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

FIG. 2 is an equivalent circuit diagram of the circuit of FIG.

FIG. 3 is a characteristic diagram showing a tuning characteristic of the circuit of FIG.

[Explanation of symbols]

 1 Tuning circuit 10 Variable gain amplifier 11, 21, 31 Differential amplifier 12, 13, 22 Current mirror circuit 30 Buffer circuit L11 Bar antenna coil Q13 Constant current source Q23 Variable constant current source

Claims (2)

[Claims] 1. A phase inversion type variable gain amplifier, a capacitor connected between an input terminal and an output terminal of the variable gain amplifier, and an external connection terminal connected to the capacitor, By the variable gain amplifier, the capacitance of the capacitor viewed from the connection terminal is almost multiplied by the voltage gain of the variable gain amplifier, and when a coil is connected to the external connection terminal, the coil and the capacitor By configuring the tuning circuit and changing the voltage gain of the variable gain amplifier,
The tuning frequency of the tuning circuit is changed I
C. 2. An IC having a phase inversion type variable gain amplifier, a capacitor connected between an input terminal and an output terminal of the variable gain amplifier, and an external connection terminal connected to the capacitor, A tuning coil externally attached to the external connection terminal, wherein the capacitance of the capacitor as viewed from the external connection terminal is made approximately double the voltage gain of the variable gain amplifier by the variable gain amplifier, By changing the voltage gain of the variable gain amplifier,
A tuning circuit that allows the tuning frequency to be changed.