JPS60102011A - Input matching circuit - Google Patents

Abstract

PURPOSE:To widen the band of matching characteristics and to realize adaption to the input matching of a microwave integrated circuit by using the emitter input impedance of a transistor (TR) as the impedance for matching an amplifier circuit input. CONSTITUTION:An emitter input circuit for a TR consists of resistances 16, 17, and 20, and a TR19. When its input impedance is Rin2 and the input impedance of a TR8 is Rin1, the total input impedance is the parallel impedance of Rin1 and Rin2. The current amplification factors of both TRs are almost equalized to each other, resistances 9 and 20 are set sufficiently large, and resistances 16 and 17 have proper values. Then, Rin1>>Rin2 and the total input impedance Rin is equalized to Rin2. Consequently, matching is possible as to even a low-impedance signal source and a transmission line, and the purpose is attained.

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to an input matching circuit that performs broadband low impedance matching at the input section of an amplifier circuit.

Prior Art and Problems Figure 1 shows a configuration example of a conventional input matching circuit, in which 1 is a high potential power supply terminal, 2 is a low potential power supply terminal, 3 is an AC voltage signal source, and 4 is a signal source impedance or a transmission line. Characteristic impedance (Rs), s-line capacitance, 6 is resistance (R1), 7
8 is a resistor (R2), 8 is an emitter follower transistor, 9 is a resistor (R,), and 1o is a circuit network such as a high input impedance amplifier circuit. The input impedance Rin of this circuit is given by the following equation, where β is the current amplification factor of the emitter follower transistor 8.

β is generally a value of about 100, and by using a large value with R, equation (1) can be expressed as R8・R8/
(Rs + 4), and by arbitrarily setting the values of R1 and R2, a desired input impedance value can be obtained. However, when this circuit is applied as a matching circuit with low impedance line Mlr (Rs = 50Ω or 75Ω) used in microwave circuits, etc., R1 and R
1 becomes a small resistance value.

Therefore, there was a problem that a large current flows and power consumption increases. Also, to avoid this, resistor '1 # R
If 210,000 is set to a low resistance value (50Ω or 75Ω) and the other is set to a high resistance value, the potential of the emitter of the emitter follower transistor 8, which is the connection point of the resistors 6 and 7 and the output terminal, increases to a high potential or a low potential. This causes problems such as the need to add a level shift circuit or the like in order to connect directly to an amplifier circuit or the like in the next stage.

Also, when trying to obtain wideband input matching characteristics,
In equation (1), there is also a problem that the current amplification factor β decreases at high frequencies, and the input impedance decreases.

FIG. 2 also shows a configuration example of a conventional input matching circuit, and the same parts are indicated by the same numbers as in FIG.
is an input transistor, and 12 is a load resistance (Rz).

15 is a feedback resistor (R7), and 14 and 15 are diodes. This circuit is a parallel feedback amplifier circuit using a feedback resistor Ry, and the input impedance Rin can be expressed by the following equation, where the input resistance of the input transistor 11 is rir&, and the voltage gain is Ao.

Therefore, by optimizing the value of the feedback resistor R1, it is possible to achieve a low input impedance (50Ω = 750Ω). However, the DC level of the emitter of the emitter follower transistor 8, which is the output terminal, is uniquely determined, and this poses a problem in that it becomes a major constraint on the design of the DC level in integrated circuits where it is difficult to connect circuits due to large capacitance. Furthermore, at high frequencies, there is a problem that wideband matching characteristics cannot be obtained because the input resistance Tin in Equation 21 decreases.

Furthermore, although there are circuits that utilize the filter characteristics of inductance and capacitance in the conventional circuits shown in Figures 1 and 2, they are limited to a single frequency and cannot be integrated into inductance and large capacitance values. There's a problem.

Purpose of the Invention In order to eliminate these drawbacks, the present invention uses a low input impedance from the emitter of a transistor as a matching impedance.The purpose of the present invention is to ensure wide-band low impedance matching characteristics and to easily integrate integrated circuits. The drawings will be described in detail below.

Embodiment of the Invention FIG. 3 shows an embodiment of the present invention, in which the same parts as in FIG. 1 are designated by the same numbers, and 16 is a resistor (R
s), 17 is a resistor (Rs), 19 is a transistor,
20 is a resistor (R5). The input impedance l1ih of the circuit of the present invention is the emitter power transistor 8
0 human power impedance is Ri mill, transistor 1
If R1n2 is the input impedance from the emitter of 9, then the parallel impedance of Ri mil and Riv&2 becomes as shown in the following equation.

Furthermore, transistor 8. Assuming that the current amplification factors of the transistors 19 are R8 and R2, and the value (RII) of the resistor 20 is a sufficiently large value (more than Ω in number), Rin+
, R1n2 is given by R141"β, , R,...(4) RirL2 = R/β, -(5).

Here, in equation (4), the value of resistance R, is sufficiently large (
Ω or more), β1. β, has a similar value (generally 1
00), and if R1n1) R1n2 holds true, the denominator RirL2 can be ignored in formula β), and R1n=
It becomes R1n2. (51, using formula (6), R number R/β = R8・R4/(R2・(71s +R4)
) ...(71. That is, the input impedance Rin is determined by the input impedance from the emitter of the transistor 19. Therefore, from the (force formula), a low impedance signal source or a transmission line (R5 = 50Ω, 7
Since β is generally about 100, matching with 5Ω) is possible by setting 83°R4 so that the value of the parallel resistance R is equal to or larger than Ω. At this time, R3
. Can be set to .

Note that in the above case, transistor 8 does not need to be an emitter follower transistor, and may be an amplifier circuit with high input impedance. In equation (4), the value of R is relatively small, and the value of R1n1 and Rir & 2. When the values are the same, Equation (51) becomes from Equations (4) and (5), and the values of β1.β decrease at high frequencies, so that broadband matching characteristics can be obtained.

In this case as well, the transistor 8 does not need to be an emitter follower transistor, and may be an amplifier circuit that has a relatively low input impedance and whose input impedance decreases at high frequencies.

FIG. 4 shows another embodiment of the present invention. In FIG. 3, 18 A correction capacitor Q shown in FIG. 1 is added in parallel with the resistor 16 or 17. The input impedance Ein of this circuit can be expressed by the following equation by adding a capacitance C in parallel to R in equation (5) above.

At high frequencies, β decreases, but the term (10)ωCR) in equation (9) increases and is compensated for, making it possible to obtain broadband matching characteristics.

FIG. 5 shows still another embodiment of the present invention, in which the same parts as in FIG. is a transistor, and 24 is a resistor (R1). The input impedance Ris of this circuit is as follows: the current amplification factor of the transistor 19.25 is R2, β, the input impedance of the transistor 80 is sufficiently high < (when the Rx car is large), and each resistor n
, , Assuming that the values of R6 and E are sufficiently large and can be ignored, the input impedance from the base of the transistor 26 is R3・R3, which is the transistor 1.
Turn on the emitter of 9, 1/β! Since it is multiplied, Rin = 5, n, −(1°) β.

becomes. When similar transistors are used as transistors 19 and 23, (10) Equation 1, Rin = Ra
It is affected by the current amplification factor of the transistor, which decreases at high frequencies, and by temperature fluctuations.

As described in detail, the input matching circuit of the present invention has a pace connected to a high potential power supply and a low potential power supply through impedances, respectively, and the collector is directly connected to the high potential power supply and the emitter is connected to the high potential power supply and the low potential power supply respectively. A low-impedance signal source that includes a transistor connected to a low-potential power supply ζ2 through a resistor, and uses the emitter input impedance of this transistor as a matching impedance to match the signal source with the input of the amplifier circuit. Alternatively, it is possible to easily match the characteristic impedance of the transmission path, and at this time, it is possible to achieve a wide band matching characteristic. Further, since the input matching circuit of the present invention consumes low power and can be integrated into an integrated circuit, it is effective as an input matching circuit in a microwave integrated circuit.

[Brief explanation of the drawing]

Figures 1 and 2 are configuration examples of conventional input matching circuits,
FIG. 3, FIG. 4, and FIG. 5 each show an embodiment of the present invention. 1...High potential power supply terminal, 2...Low potential power supply terminal, 6
... AC voltage signal source, 4... Signal source impedance or characteristic impedance of transmission path, 5... Container lid, 6
゜7...Resistor, 8...Emitter follower transistor, 9...Resistor, 10...Circuit network such as high input impedance amplifier circuit, 11...Human power transistor,
12...Load resistance, 15...Feedback resistance, 14.15
...Diode, 16° patent applicant Nippon Telegraph and Telephone Public Corporation agent Patent attorney Gobe Tamamushi (2 others) Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] (1) In an input matching circuit that matches a signal source and an input of an amplifier circuit via a matching impedance, a base is connected to a high potential power source and a low potential power source through impedances, and a collector is connected to a high potential power source and a low potential power source through impedances. It is characterized by comprising a transistor connected directly to a high potential power source and having its emitter connected to a low potential power source via a resistor, and matching the signal source and the amplifier circuit input using the emitter input impedance of the transistor as the matching impedance. input matching circuit. (2) The impedance connecting the pace to the high potential power source and the low potential power source is characterized by comprising a resistor connected between the base and the high potential power source and a resistor connected between the pace and the low potential power source. A matching circuit according to claim 1. (5) The impedance that connects the pace to the high potential power source and the low potential power source is either a resistor connected between the base and the high potential power source, a resistor connected between the base and the low potential power source, or each of the resistors. 2. The input matching circuit according to claim 1, further comprising a capacitor connected in parallel with a capacitor. (4) The impedance connecting the base to the high potential power supply and the low potential power supply includes a resistor connected between the base and the high potential power supply, a resistor connected between the pace and the low potential power supply, and a resistor connected between the base and the low potential power supply, and the impedance connecting the base to the high potential power supply and the low potential power supply. 2. The input matching circuit according to claim 1, further comprising another transistor having a collector connected directly to a high potential power source and an emitter connected to a low potential power source via a resistor.