JPH03255711A - Intermediate frequency amplifier circuit - Google Patents

Abstract

PURPOSE:To make an intermediate frequency amplifier circuit compact while stablizing an operation by executing direct current feedback by making a feedback voltage related to the direct current feedback from a differential amplifier in the final step almost equal with the bias voltage of a transistor in the first step. CONSTITUTION:An intermediate frequency amplifier circuit 56 is equipped with a transistor 58 and a constant current circuit 60 so as to apply the prescribed feedback voltage to the output from a transistor 22-4 of an operational amplifier 20-4 in the final step. Further, the emitter output of this transistor 58 is inputted through an LPF, which is composed of a resistor 34 and a capacitor 38, to the base of a transistor 24-1 in the first step. On the other hand, a transistor 62, constant current circuit 64, resistor 66 and capacitor 68 are provided to apply the prescribed bias voltage between the base and collector of the transistor 22-1. Thus, the intermediate frequency amplifier circuit 56 can be realized with high gain and high stability while reducing phase rotation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an intermediate frequency amplification circuit used in FM radio and the like, and particularly relates to an improvement in DC feedback means.

[Prior Art] For example, in an integrated AM/FM radio receiver, an intermediate frequency amplification circuit integrated in - ICs is used.

FIG. 3 shows an example of the configuration of a conventional intermediate frequency amplification circuit.

The intermediate frequency amplification circuit 10 according to this conventional example includes one IC.
It is configured as. This intermediate frequency amplification circuit 10 includes an intermediate frequency (IF) signal input terminal 12, a power supply terminal 14,
DC feedback capacitor terminals 16 and 18 are provided.

A frequency selection filter 19, which is a piezoelectric ceramic filter, for example, is connected to the IF signal input terminal 12.
An IF multiplied signal of 10.7 MHz is input to this frequency selection filter 19 from the outside, for example, from a mixer. One frequency selection filter passes only a desired IF band and supplies it to the intermediate frequency amplification circuit 10.

Further, the power supply terminal 14 supplies the DC voltage Vcc to the intermediate frequency amplification circuit 10 as a power supply voltage.

In this conventional example, the intermediate frequency amplification circuit 10 has a four-stage configuration. That is, the differential amplifier 20 has a configuration in which four stages are connected in cascade.

In each stage of the differential amplifier 20, transistors 22 and 24 are connected as a pair, and the emitters of the transistors 22 and 24 are both connected to a constant current circuit 26, while the collectors thereof are connected to a resistor 28 and a resistor 28 having approximately the same resistance value, respectively. It has a configuration in which it is connected to the power supply terminal 14 via 30.

In addition, the collectors of the transistors 22 and 24 in each stage are
It is connected to the bases of transistors 22 and 24 in the next stage. Therefore, the differential amplifier 20 in each stage has a power supply voltage Vc
The signal that is driven with a constant current by the constant current circuit 26 and supplied to the base from the transistor 22 or 24 in the previous stage is amplified with a constant current and is supplied to the differential amplifier 20 in the next stage.

Here, the transistor 22 of the first stage differential amplifier 20-1
The above-mentioned IF signal input terminal 12 is input to the base of -1. As a result, I
The F-fold signal is input and differentially amplified by the differential amplifier 20-1. Furthermore, the signal is sequentially supplied to the differential amplifier 20 at the subsequent stage, and is amplified in multiple stages. As a result, the amplified IF times signal is output from the collectors of the transistors 22-4 and 24-4 of the differential amplifier 20-4 at the last stage.

Further, in order to operate this circuit 10 stably, resistors 32 and 34 and capacitors 36 and 38 are provided. The resistor 32 and capacitor 36, the resistor 34 and the capacitor 38 are connected to low pass filters 40 and 4, respectively.
2.

That is, the last stage transistors 24-4 and 22-4
The collectors of are connected to one ends of resistors 32 and 34, respectively, and the other ends of resistors 32 and 34 are connected to capacitors 36 and 38 via DC feedback capacitor terminals 16 and 18.
It is connected to the.

Furthermore, these terminals 16 and 18 are connected to the bases of transistors 22-1 and 24-1, respectively, via an impedance matching resistor 44 or directly.

As a result, the outputs from the transistors 24-4 and 224 are low-pass filtered by the low-pass filters 40 and 42, and only the DC component is output from the transistors 22-1 and 22-1.
It is fed back to 4-1.

Further, impedance matching with the frequency selection filter 20 is maintained by the impedance matching resistor 44.

Note that in this circuit 10, for example, the resistors 28 and 30
is approximately Ω in number, the impedance of the frequency selection filter 20 is approximately 300Ω, the impedance matching resistor 44 is set to a value corresponding to the impedance of the frequency selection filter 20, and the capacitors 36 and 38 are set to approximately 0.01 μF. Also, resistors 28-4 and 30-1. Constant current circuit 26-1
and 26-4 have almost the same resistance value and current value, respectively.

In this conventional example, the circuit operation is stabilized by direct current negative feedback, but external capacitors 36 and 38 and terminals 16 and 18 for connecting these are required, which is contrary to integration and reduces the size of the device. It becomes a hindrance.

FIG. 4 shows another example of the configuration of a conventional intermediate frequency amplification circuit.

The conventional intermediate frequency amplification circuit 46 shown in this figure is as follows:
The collector of the transistor 22-4 is connected to the base of the transistor 24-1 as in the conventional example shown in FIG.
-1 is not connected to the base.

That is, the external capacitor 38, the impedance matching resistor 44, the DC blocking capacitor 48, and the IF
It is connected to the base of the transistor 22-1 via the signal input terminal 12, and connected between the base and emitter of the transistor 22-1 through a resistor 32. Further, the resistor 32 is connected between the base and collector of the transistor 22-1.

Here, since the impedance matching resistor 44 has a low resistance, the feedback needle is negligible with respect to the input from the frequency selection filter 19, or because the resistor 32 is provided as described above, the transistor 22 -1 will also be fed back.

Therefore, in this conventional example, since DC feedback is provided only from the transistor 22-4, it is possible to reduce the number of external capacitors and downsize the device compared to the conventional example shown in FIG.

Further, FIG. 5 shows the configuration of an intermediate frequency amplification circuit 50 according to a third conventional example.

The circuit 50 shown in this figure does not employ DC feedback, and connects the coupling capacitor 5 between the differential amplifiers 20 at each stage.
2 and 54.

Therefore, according to this conventional example, external capacitors and their terminals that are required due to DC feedback are no longer necessary, and the device configuration is further miniaturized.

[Problems to be Solved by the Invention] However, in the conventional example shown in FIG. 5, a parasitic capacitor is generated in the thickness direction of the substrate, and AC feedback occurs. That is, in an intermediate frequency amplifier circuit integrated on a semiconductor substrate as an IC, such parasitic capacitors may occur, resulting in unnecessary AC feedback and unstable operation.

As described above, conventionally, depending on the circuit configuration, one of two problems has occurred: instability of the circuit operation and hindrance to miniaturization due to the need for external parts.

The present invention has been made to solve these problems, and it is an object of the present invention to provide an intermediate frequency amplification circuit that is stable in operation and has a small number of external parts.

[Means for Solving the Problem] In order to achieve such an object, the present invention applies a predetermined feedback voltage to the output from a predetermined transistor among the transistors included in the last stage differential amplifier, and Among the transistors included in the differential amplifier, DC feedback means inputs feedback to a predetermined transistor, and among the transistors included in the first-stage differential amplifier, DC feedback is applied to a transistor different from the transistor related to the feedback input from the DC feedback means. It is characterized by having a bias means for applying a bias voltage substantially equal to the feedback voltage by the feedback means.

[Operations] In the present invention, among the amplified IF multiplied signals output from the last stage differential amplifier, a predetermined feedback voltage is given by the IF multiplied signal DC feedback means related to the output of a predetermined transistor, and It is fed back to the differential amplifier. This IF multiplied signal is input to a predetermined transistor among the transistors constituting the first stage differential amplifier. A bias voltage is applied to the other transistors constituting the first-stage differential amplifier by bias means.

At this time, the feedback voltage given by the IF multiplied signal by the DC feedback means and the bias voltage applied to the transistor by the bias means are equal voltages. Further, since both the DC feedback means and the bias means are integrally constructed using transistors and the like, stable DC feedback can be realized while reducing the number of external parts.

[Examples] Hereinafter, preferred embodiments of the present invention will be described based on the drawings. Components similar to those of the conventional example shown in FIGS. 3 to 5 are denoted by the same reference numerals, and explanations thereof will be omitted.

FIG. 1 shows the configuration of an intermediate frequency amplification circuit according to a first embodiment of the present invention.

The intermediate frequency amplification circuit 56 shown in this figure includes a transistor 58 that applies a predetermined feedback voltage to the output of the transistor 22-4 of the final stage differential amplifier 20-4, and a constant current circuit 6.
Contains 0. That is, the amplified IF multiplied signal output from the collector of the transistor 22-4 is input to the base of the transistor 58, which is driven by the constant current circuit 60 with a constant current twice that of the constant current circuit 26. Ru. Therefore, the feedback voltage applied to the IF signal by the transistor 58 has a predetermined value corresponding to the current value of the constant current circuit 60.

Further, the emitter output of this transistor 58 is inputted to the base of the first stage transistor 24-1 via an LPF consisting of a resistor 34 and a capacitor 38, as in the conventional example shown in FIG.

Further, in this embodiment, transistor 62.1 applies a predetermined bias voltage between the base and collector of transistor 22-1. A constant current circuit 64 includes a resistor 66 and a capacitor 68. That is, the constant current circuit 60 described above
When the current value of the constant current circuit 64 and the current value of the constant current circuit 64 are equal, the transistor 5 is connected between the collector and emitter of the transistor 62.
A voltage equal to the collector-emitter voltage (feedback voltage) of No. 8 is generated. Therefore, a bias voltage equal to the feedback voltage from transistor 58 is applied to transistor 22-1.

Note that the resistor 44 is an impedance matching resistor, and the resistor 66 is
and capacitor 68 are LPFs related to the input to transistor 221.

Therefore, according to this embodiment, since the IF multiplied signal related to the output of the transistor 22-4 is fed back as DC feedback, the intermediate frequency amplifier circuit 56 with a small phase shift and high gain and high stability can be obtained. Further, since one of the LPFs related to DC feedback can be configured by integrating the resistor 66 and the capacitor 68, the number of external parts is reduced and the device configuration is made smaller.

FIG. 2 shows the configuration of an intermediate frequency amplification circuit 70 according to a second embodiment of the present invention. In this figure, the first
Only the parts that are different in structure from the illustrated embodiment are shown.

In this embodiment, the LPF associated with transistor 62
is constructed using a Darlington connection of transistors 72. That is, the transistor 72 connected to the collector or base of the transistor 22-1 is connected to the base of the transistor 62 via the emitter or one end of the capacitor 68.

As a result, the capacitance value of the capacitor 68 becomes smaller than that in the embodiment shown in FIG. 1, and the circuit becomes more compact.

[Effects of the Invention] As explained above, according to the present invention, the feedback voltage related to DC feedback from the final stage differential amplifier and the bias voltage of the first stage transistor are made almost equal, thereby reducing DC feedback. This reduces the number of external parts and reduces the size of the circuit while stabilizing the operation.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a configuration of an intermediate frequency amplification circuit according to a first embodiment of the present invention, FIG. 2 is a circuit diagram showing a configuration of an intermediate frequency amplification circuit according to a second embodiment of the present invention, FIG. 3 is a circuit diagram showing a configuration example of a conventional intermediate frequency amplification circuit, FIG. 4 is a circuit diagram showing another configuration of a conventional intermediate frequency amplification circuit, and FIG. 5 is a circuit diagram showing a configuration example of a conventional intermediate frequency amplification circuit. FIG. 3 is a circuit diagram showing the configuration of a third configuration example of the frequency amplification circuit. 20... Differential amplifier 22.24.58, 62.72... Transistor 56.70... Intermediate frequency amplification circuit 60, 64
... Constant current circuit 66 ... Resistor 68 ... Capacitor

Claims (1)

[Claims] A plurality of transistors are differentially connected, and a predetermined number of stages of differential amplifiers are provided for differentially amplifying and outputting an intermediate frequency signal input to one transistor, and the differential amplifiers are sequentially connected. In an intermediate frequency amplification circuit that differentially amplifies an intermediate frequency signal in multiple stages, a predetermined feedback voltage is applied to the output from a predetermined transistor among the transistors included in the last stage differential amplifier, and DC feedback means for feedback input to a predetermined transistor among the transistors, and a transistor different from the transistor related to the feedback input from the DC feedback means among the transistors included in the first stage differential amplifier, with a feedback voltage approximately equal to the feedback voltage from the DC feedback means. An intermediate frequency amplification circuit comprising: bias means for applying equal bias voltages;