JPH0416005A - High frequency amplifier circuit - Google Patents

Abstract

PURPOSE:To improve the distortion characteristic and the band characteristic by providing a common emitter differential amplifier of a pre-stage comprising a couple of transistors TRs) whose emitters connect to ground and a common base differential amplifier of a post-stage comprising a couple of TRs whose bases are connected in common. CONSTITUTION:When a high frequency signal is fed to input terminals A, B via a band pass filter, a signal amplified by a common emitter differential amplifier of a pre-stage is outputted from collectors of TRs Q1, Q2 and inputted to emitters of TRs Q3, Q4 of a common base differential amplifier of the post- stage via resistors R5, R6, amplified by the differential amplifier of the post-stage and outputted from output terminals C, D via collectors of the TRs Q3, Q4. In this case, since the resistors R5, R6 are inserted respectively between the differential amplifiers of the post and pre-stage, the load impedance of the differential amplifier of the pre-stage is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a high frequency amplifier circuit applied to high frequency equipment such as a television tuner and a CATV converter.

[Prior Art] Among this type of high frequency amplifier circuit, what is called a differential cascode connection amplifier circuit has conventionally been constructed as shown in FIG. In this diagram, transistor Q
,,Q constitutes the front stage differential amplifier, and transistors Q3Q4 constitute the rear stage differential amplifier 81! has been completed.

Transistors Q1 and Q of the front-stage differential amplifier.

High frequency input terminals B and A are respectively connected to each l\- source, and a bias voltage VB is also supplied through resistors R3 and R4, respectively. Mafco, transistor Q
Impedance elements R1 and R7 connected in series are connected between the respective emitters of 1 and Q, and the connection point of these impedance elements R and R7 is grounded via a current source I.

As a result, the front-stage differential amplifier is a common emitter differential amplifier.

On the other hand, transistors Q3 and Q4 of the differential amplifier in the subsequent stage
The bases of are commonly connected, and choke coils L and RI connected in series are connected between each collector, and the connection point of these choke coils L and RI is connected to a power supply terminal Vcc.

Further, the collectors of transistors Q and Q4 are connected to output terminals C and D, respectively. As a result, the differential amplifier at the subsequent stage is a common base type differential amplifier.

And the transistors Q and Q of the differential amplifier in the previous stage,
Each collector of the transistor Q of the subsequent differential amplifier,
and Q4 respectively, thereby connecting transistors Q and Q2 to the respective emitters of transistors Q and Q4.
4 is cascade-connected as a load to form a differential cascode-connected amplifier circuit.

In such a configuration, when a high frequency signal is supplied to input terminals A and B via a bandpass filter (BPF), the signal amplified by the common emitter differential amplifier in the previous stage is transmitted to the transistors Q, Q2. This signal is outputted from the collector, and further amplified by a common-base differential amplifier in the subsequent stage, and outputted from output terminals C and D via the collectors of transistors Q, , Q.

[Problem to be solved by the invention] By the way, in the conventional high frequency amplifier circuit described above,
There were the following problems.

(2) Either the output of the front-stage differential amplifier is input to the rear-stage common-base differential amplifier, or the input impedance of the common-base differential amplifier is generally low, about 10-odd ohms. As a result, the load impedance of the differential amplifier at the front stage that uses this as a load becomes low, and deterioration of distortion characteristics is unavoidable, resulting in deterioration of distortion characteristics such as cross-modulation and intermodulation in the entire high-frequency amplifier circuit. This is clear from the simulation using non-linear software (microwave harmonica) from Compact, USA.

■A high-frequency signal is input through a band-pass filter, but because the load impedance of the differential amplifier in the previous stage is extremely low, the input impedance of that differential amplifier becomes a negative resistance, which causes the load of the band-pass filter. As a result, there arises a problem that the flatness within the band of the bandpass filter deteriorates and the bandwidth becomes narrow. In particular, recent transistors have a high gain-bandwidth product Ft, and this problem becomes noticeable.

■Since the input impedance of the differential amplifier in the previous stage becomes a negative resistance, it is difficult to obtain impedance matching with the bandpass filter.If, for example, a resistor is added to eliminate this negative resistance, transmission loss will occur. becomes larger,
A new problem arises in that the NF (noise figure) worsens.

■Since the differential amplifier in the latter stage is a base-grounded type, the output impedance is high and positive feedback is likely to occur from the output.Also, the differential amplifier in the previous stage has a low load impedance, so transistors Q1 and Q are connected to the collector. This results in the formation of a type oscillator, which tends to cause abnormal oscillation.

This invention was made in view of the above-mentioned circumstances, and it is possible to improve distortion characteristics and band characteristics, easily obtain impedance matching with the preceding circuit, and prevent abnormal oscillation. The purpose is to provide a high-frequency amplification circuit that can perform

[Means for Solving the Problems] A high-frequency amplifier circuit according to the present invention includes a common-emitter differential amplifier in the preceding stage, which is constituted by a pair of transistors whose respective emitters are grounded, and a common-emitter differential amplifier at the front stage, which is constituted by a pair of transistors whose respective emitters are grounded, and whose respective emitters are connected to each collector of the pair of transistors. The device is characterized in that it is provided with a common-base differential amplifier at the subsequent stage, which is constituted by a pair of transistors connected to each other via a resistor, and whose bases are commonly connected.

[Function] According to the above configuration, the load impedance of each transistor of the common emitter differential amplifier in the previous stage is increased, thereby improving the distortion characteristics and band characteristics, and further improving the impedance matching with the circuit in the previous stage. It is easily obtained and abnormal oscillations are prevented.

[Example=1 Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing the configuration of a first embodiment of the present invention,
Components corresponding to those in FIG. 3 are given the same reference numerals, and their description will be omitted.

In FIG. 1, the collectors of transistors Q and Q constituting the common emitter differential amplifier in the previous stage are connected to the emitters of transistors Q3 and Q4 of the common base differential amplifier in the subsequent stage via resistors R6 and R8. are connected to each other. This causes the transistor Q to have a resistor R
5 and transistor Q are connected in cascade as a load, resistor R@ and transistor Q4 are connected to transistor Q,
The circuit consists of a differential cascode-connected amplifier circuit in which cascodes are connected in cascade as a load.

In such a configuration, when a high frequency signal is supplied to input terminals A and B via a bandpass filter, the signal amplified by the common emitter differential amplifier in the previous stage is transmitted from the collectors of transistors Q,, Q, Furthermore, the transistor Q8 . It is input to the emitter of Q, and after being amplified by the differential amplifier at the subsequent stage, it is output to the output terminals C and D via the collectors of transistors Q s and Q 4.
is output from.

In this case, since resistor R6 and resistor R6 are inserted between the front-stage and rear-stage differential amplifiers, the load impedance of the front-stage differential amplifier is higher than in the past, and the voltage distortion of the front-stage differential amplifier increases. This improves the distortion characteristics of the high frequency amplifier circuit as a whole. This is clearly demonstrated by the nonlinear software (Microwave Harmonica) from Compact, USA.

In addition, since the load impedance of the front-stage differential amplifier is set to an appropriate value by the resistors R5 and R6, the input impedance does not become a negative resistance. It is possible to improve the impedance matching between the differential amplifier in the front stage and the bandpass filter, and to reduce the matching loss. Oscillation is prevented.

Next, FIG. 2 is a diagram showing the configuration of a second embodiment of the present invention. In addition to the above-mentioned first embodiment, there is a A resistor R7 and a resistor Re are connected to each of the resistors R7 and Re to form a single configuration.

In the second embodiment as well, as in the first embodiment, it is possible to improve the distortion characteristics and bandpass characteristics, and it is also possible to easily obtain impedance matching between the differential amplifier and bandpass filter in the previous stage, and to improve these characteristics. In addition, by providing resistors R9 and R6, the stability (knurling stability coefficient K) of the differential amplifier in the subsequent stage can be increased, thereby completely preventing abnormal oscillations in the differential amplifier in the subsequent stage. It can be prevented. In this case, since the differential amplifier at the subsequent stage is of a common base type, its signal source impedance is much higher than the values of resistors R9 and Re, and therefore smaller than the output signal loss due to resistors R7 and R8. Also,
Since the subsequent differential amplifier has high stability, it becomes easy to design the impedance conversion circuit and the bandpass filter circuit, and the degree of freedom in design can be improved.

[Effects of the Invention] As explained above, according to the present invention, the load impedance of each transistor of the common emitter differential amplifier in the previous stage is increased, so that distortion characteristics and band characteristics can be improved. At the same time, it is possible to easily obtain impedance matching with the circuit at the previous stage, and it is possible to prevent abnormal oscillations.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of a first embodiment of the invention, FIG. 2 is a circuit diagram showing the configuration of a second embodiment of the invention, and FIG.
The figure is a circuit diagram showing the configuration of a conventional high frequency amplifier circuit. Q,,Q,...transistor (common emitter differential amplifier), Q3. Q, ・Transistor (grounded differential amplifier), Ra, R-, R1, Rs"'resistance.

Claims (2)

[Claims] (1) A front-stage common emitter differential amplifier consisting of a pair of transistors whose emitters are grounded; each emitter is connected to each collector of the pair of transistors via a resistor; and each base is 1. A high-frequency amplification circuit comprising: a common-base differential amplifier at a subsequent stage configured by a pair of commonly connected transistors; (2) The high frequency amplifier circuit according to claim 1, wherein the output of the collector of each transistor of the common base differential amplifier is outputted via a resistor.