JPH04160808A - Microwave low noise amplifier - Google Patents

Abstract

PURPOSE:To minimize an NF of a FET and to decrease an input side VSVW simultaneously by connecting a connection part between a source electrode and a capacitor to ground via an inductor or a transmission line. CONSTITUTION:An input side reflection coefficient (GAMMANopt) minimizing a noise figure NF of a FET and an input side reflection coefficient (GAMMAS) are made close to each other by the action of a capacitor connected between a drain and a source of the FET and a feedback component of the FET. In this case, when a capacitor Cds is not added, the coefficients GAMMANot, GAMMAS differ from each other largely, they are made close to each other attended with the increase on the capacitor Cds, and when the Cds increases, they are again parted. Thus, the optimum Cds making the coefficients GAMMAS, GAMMANot closest is in existence. Thus, the NF of the FET and the input VSWR are made small simultaneously.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to microwave low noise amplifiers.

(Prior Art) In recent years, as field effect transistors (hereinafter abbreviated as FET) and high electron mobility transistors (hereinafter abbreviated as HEMT) made of GaAs-based and InP-based materials have progressed,
Attempts to monolithically fabricate these transistor matching circuits, Piano circuits, etc. on semiconductor substrates are being actively made in various places. This monolithic IC is MM IC
(nteg on Monolithic Microwave
Hybrid microwave I
C (MIC: Microwave or tegra
It is smaller and has superior reliability compared to the tedan1rcuit. For this reason, various low-noise amplifiers, mixers, oscillators, etc.
MICs are being developed in various places and are contributing to the miniaturization of microwave transmitters and receivers. Especially recently, FET-? The noise of HEMTs has been significantly reduced, and accordingly, the noise of microwave receivers has also been reduced.
eFigure) has been improved to about 1 dB.

Microwave receivers are required to have low noise, but
The key device is the low-noise amplifier at the first stage of the receiver. Normally, when designing a low-noise amplifier, a matching circuit is designed to minimize NF on the input side of the first-stage FET, and maximize gain between the FETs and on the output side of the final-stage FET. FET
NFHlFET input (11111 (usually between gate and source) to power supply 1111't reflection coefficient (/'S)
, the minimum noise figure NFm of the FET, the input side reflection coefficient 7'Nopt given to NFm', and the equivalent noise resistance Rn of the FET.
It is expressed by the following equation using f. (Reference: Figure 5, 1:
1ntrinsicFET, 6: Inductor) NF =NFm+4 *Rn* l 7'S -7"N
op t 12/(Zo*l 1+7”Nap t 1
2*(1-l 7″!3t2)) (1) Here, Zo is the characteristic impedance of the line.

Next, the input reflection coefficient r1 of the FET is calculated using the S parameter of the FET and the reflection coefficient rL of the load: 7'1=S11+
S21*S12*7"L/(1-7'L*522)
...It is expressed as (2). In addition, the output reflection coefficient r2 of the FET is calculated as follows using the reflection coefficient rS of the power supply: 7'2=S22+S21*S12*7'S/(1-7'
S*511) ・----(3) Note that 7'S and 7'L are reflection coefficients looking at the power supply and load connected from the gate and drain of the FET to the input/output side of the FET, respectively. Therefore, (2), (3)
7'5 (=complex conjugate of 7'l) and r that simultaneously satisfy the formula
If there exists a complex conjugate of L C=r 2) and their absolute value is less than 1, then FETFi is unconditionally stable, and (2)
If the reflection coefficient el(rS) k, which is the complex conjugate of the equation, is connected to the input side of the FET, the input side of the FET will be matched, and the
Wave Ratio) becomes 1.

<Problems to be Solved by the Invention> However, in general, r Nopt and rS in equation (1) do not match. In low-noise amplifiers, we place emphasis on NFk and design the input side matching circuit t-7'Nopt of the first stage FET, so
The input VSW of the low noise amplifier depends on the difference between Nopt and rS.
R becomes large. As a conventional example, the gate length is 0.5
#ya, GaAs MESFET with gate width 280μya
The S/(parameter and noise parameters at a frequency of 12 GHz are shown in the table below.

Table 1 Note that the S parameters in Table 1 are the S parameters of the two-terminal network between aa' and bb' in FIG.
These are S parameters of a circuit in which cFETI and inductor 6 are connected in series. Further, the inductor 6 represents the inductance generated when connecting the FET 1 to the reference potential a (b')k using a wire or a transmission line as an equivalent circuit element. Calculate from these S parameters Sale 7: rrsI/
10.95 < 128° Tonal Note, r Nopt and rS are far apart, and the input matching circuit of the FET is
If the design is set to "opt", a problem arises in that the input VSWR of the low-noise amplifier becomes large. FET' in Table 1
Figure 6 shows a circuit example of a one-stage amplifier using i, and the NF of the amplifier and input VSWR of 11.6 to 12.2 GHz.
Figure 7 shows the characteristics at . In Figure 6, 1 is 1nt
rinsic FET, 40 and 41 are transmission lines forming input and output matching circuits, 42 is a capacitor, 43 and 44 are voltage supply terminals for the gate and drain of the FET, respectively, and 45 and 46 are inputs and inputs of an amplifier, respectively. It is an output terminal. Note that 40.41 in Fig. 6 is a 150 μm thick GaA
It is composed of 120 μm @ microstrip lines created on a S substrate, and the physical length of each is 40a = 7.
50μyn, 40b=210μyn, 41a=L80μ
m, 41b=1060 μm. Here, the input matching circuit 40 in FIG. 6 is designed to minimize NF, and the output matching circuit 41 is designed to maximize gain. In Figure 7, 50 is NF
51 is that of the input VSWR.

From the characteristics shown in FIG. 7, an NF of 1.6 dB or less is obtained within the band, but the input VSWR is at most 2.3 within the band.

As described above, conventional low-noise amplifiers have a problem in that input VSWR must be significantly sacrificed in order to minimize NF. In view of the drawbacks of the conventional example, the present invention minimizes the NFi of the FET and simultaneously increases the input side VSW.
The present invention provides a microwave low noise amplifier that does not sacrifice much of R'i.

<Means for Solving the Problems> The microwave low noise amplifier of the present invention has an output side of an FET,
That is, the device is characterized in that a capacitor is connected between the drain and the S/N, and the capacitor and the S/N electrode of the FET are grounded via an inductor or a transmission line.

<Function> In the present invention, the FET is
Input side reflection coefficient (rNopt) that minimizes the NF of ET
and the input side reflection coefficient (rs
) approaches. Therefore, in a conventional low-noise amplifier, the first stage F
In order to minimize the NFi of the FET, the input side matching circuit of the FET is
The input VSWR of the low-noise amplifier deteriorated in proportion to the SCI distance, but according to the present invention, r Nopt and rS'fI can be made very close to each other, so
While reducing the NF of the low noise amplifier, the input VSWII
It is possible to make it smaller.

<Example> The present invention will be explained in detail by giving examples below.

An embodiment of the present invention is shown in FIG. In Figure 1, 1
are the FET, 2.8.4 are the gate, drain, and source terminals of FET1, respectively, 5 is the reference potential of the microwave signal input and output to FET1, and the signal is input between terminals 2 and 5, and between terminals 3 and 5. is output from. 6 is an inductor which is connected to the source terminal of FETI and the reference potential. This inductor 6 represents, as an equivalent circuit element, the inductance that occurs when the FETI and the reference potential 5 are connected using a wire or a transmission line. 7 is a capacitor Cds connected in parallel to the output side of FETI. In FIG. 1, the reflection coefficients on the load side and the power supply side that simultaneously match the input and output of the FET are respectively rS and 7'L, and the reflection coefficient on the input side that minimizes the NF of the FET is rNopt. FIG. 2 shows the results of calculations as functions of rS and rNoptt-Cds at 12 GHz using a FET with conventional characteristics (Table 1) as the FETI. (The S parameter of FETI in Figure 1 is obtained by de-embedding the inductance 0.08 nH in Figure 1.6 from the S parameter in Table 1.
Then, Cds and inductance 0.08 n
Figure 2 was calculated using Hf embedded. ) In Figure 2, 10 is the locus of rS when Cds changes, Cd5=QpF is point A, and Cd5=0.8pF is point B.
, and as Cds increases, FS changes in the direction of the arrow. -10,000, rNopt does not change significantly even if Cds changes and is at point 11. It is clear from Figure 2 that Cd
When adding s (Sunawachi, Cd5=OpF), r
S and 7'Nopt are significantly different, and as Cd50 increases, they tend to approach each other, and as Cds increases, they tend to separate again. Therefore, there is an optimal Cds value where 7'S&rNopt is closest, and at that time FETI
NF and input VSWRt can be reduced at the same time. Also, even if Cds is changed, the NFm of the FET
does not have much influence. Therefore, the first stage F of the low noise amplifier
By connecting a capacitor to the output side of the ET, the NF of the low noise amplifier
input VSWR? without degrading the input VSWR? It is possible to make it smaller.

Table 2.8 shows the calculation results of rS and noise parameters when there is no Cds and when Cd5=0.2 pF.

7'S 7'Nopt NFm (dB) when there is no Cds
R hard 10.95G28° 0.72<118° 1.4
5 15 Table 2 Cds=0.2pF r S rNopt NFm (dB) Rn (Ω)
0.86<117°0.73<118°1.46 15
Table 3 From the comparison in the above table, when Cds is weak, rNopt and rS
The distance is 0.26, and when Cds = 0.2 pF, the distance is 0.18, so by adding Cds, rNopt and 7'S become much closer, and as a result,
When used in a low noise amplifier, the NE and vSWR of the FET can be reduced at the same time.

Next, as another embodiment of the present invention, Cd5=0.2pF
An example of a one-stage amplifier using the FET shown in FIG. 1 is shown in FIG. 8. In addition, 11.6~ of the amplifier
FIG. 4 shows the characteristics of NF and input VSWR at 12.2 GHz. In FIG. 3, the same numbers as in FIG. 1 represent mukoji sweets.

In addition, 20 and 21 are transmission lines forming input and output matching circuits, 22 is a capacitor, and 23 and 24 are FE lines, respectively.
The gate and drain voltage supply terminals of T, 25 and 26, are the input and output terminals of the amplifier, respectively. Note that 20.21 in Fig. 3 is composed of a 120 μm wide microstrip line created on a 150 μm thick GaAs substrate, and the physical lengths of each are 20a = 690 μm, 20b =
250μm, 21a=200μm, 21b=880μm
It is m. In FIG. 4, dotted lines 50 and 51 are the NF and input VSWR of the conventional amplifier, and solid lines 60 and 61 are the NF and input VSWR of the amplifier of the embodiment of the present invention in FIG. 8, respectively.
This is the frequency characteristic of R. As is clear from the comparison in FIG. 4, in the circuit example of FIG. 3 using the present invention, the NF
Good characteristics such as L of 6 dB or less and input VSWRI of 7 or less can be obtained, and compared to the conventional example, the input VSWR can be significantly improved with almost no deterioration of NF.

The present invention has been described above in detail using examples.

Note that the present invention is not limited to these embodiments, and, for example, the present invention can be applied to amplification stages other than the first stage of a low-noise amplifier. Further, the present invention also relates to GaAs
Not only MMIC but also MM with Si and InP substrates
It is also applicable to IC and hybrid IC (MIC).

(Effects of the Invention) As explained above, according to the present invention, the input reflection coefficient for matching the input of the FET and the input reflection coefficient for minimizing the NF can be made close to each other.
- input VSWR of the amplifier without deterioration? It is possible to make it smaller.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of a microwave circuit using the present invention, and FIG. 2 is a diagram showing an example of a microwave circuit using the present invention.
Figure 8 shows a circuit example in which the present invention is applied to a one-stage amplifier. Figure 4 shows the frequency characteristics (NF and input VSWR) of the circuit example in Figure 3. diagram showing,
FIG. 5 shows the reflection coefficient F1. r2. Definition of rs, rL k Indication T Reference diagram, Figure 6 shows an example of a conventional one-stage amplifier using GaAs MESFETf, Figure 7 shows the frequency of the characteristics (NF and input VSWR) of the circuit example in Figure 6. FIG. 3 is a diagram showing characteristics. 1: FET, 2: Gate terminal of FET1, 8: FET
1 drain terminal, 4: FET1 source terminal, 5
: Reference potential of microwave signal, 6: Inductor, 7
: Capacity, 10: PS trajectory, 11 Near” Nopt,
20a, 20b: Transmission line forming the input matching circuit of FET1, 21a, 21b: Transmission line forming the output matching circuit of FETI, 22: Capacitance, 2B: F
Gate voltage supply terminal of ET1, 24: Drain voltage supply terminal of FET1, 25: Input terminal of amplifier, 26
: Amplifier output terminal, 40a. 40b: Input matching circuit, 41a, 41b: Output matching circuit, 42: Capacitor, 43: Gate voltage supply terminal, 4
4 Nidrain voltage supply terminal, 45: amplifier input terminal,
46: Output terminal of the amplifier, 50: NF of the conventional amplifier, 51: Input of the conventional amplifier VSWR160: NF of the amplifier of the present invention, 61: Input of the amplifier of the present invention ■5WR0 Agent Patent attorney Ume 1) Katsu (and 2 others) Figure 3 Shukai J & (GHK)

Claims (1)

[Claims] 1. A microwave low-noise amplifier characterized in that a capacitor is connected between the drain and source electrodes of a field effect transistor, and a connection portion between the source electrode and the capacitor is grounded via an inductor or a transmission line.