JPH01137710A - Wide band amplifier - Google Patents

Abstract

PURPOSE:To use the title amplifier over a wide range from a low band up to a high band by changing the gate lengths of FETs to be amplifier elements of respective amplifier circuits in accordance with frequency bands. CONSTITUTION:A low frequency component of an input signal is passed through a low pass filter 2L and amplified by a DC amplifier circuit Ia1. Since various parameters such as the gate lengths, gate widths, thresholds, etc., of FETs 11-14 are optimized so as to be appropriate for low frequency operation, an efficiently amplified output can be obtained. The output is sent to an output terminal through a low pass filter 3L. On the other hand, a high frequency component of the input signal is passed through a high pass filter 2H and amplified by an AC amplifier circuit Ia2. Various parameters of an FET 21 are optimized so as to be appropriate for AC operation.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention uses a field effect transistor (FET) as an amplifying element.
).

[Conventional technology]

There are various types of amplifiers such as DC amplifiers and high frequency amplifiers, and broadband amplifiers are known as having amplification characteristics over a wide frequency band from low frequency bands to high frequency bands. On the other hand, what is known as a composite amplifier is one in which frequency bands that can be amplified are spliced together. This is done by installing an AC amplifier that handles the high frequency range and a DC amplifier that handles the low frequency range in parallel, and outputs the output signal from the C, R
It is a combination of waves.

[Problem that the invention seeks to solve]

However, in the conventional device, no particular improvements have been made to the FET responsible for the low frequency range and the FET responsible for the high frequency range. For this reason, there have been drawbacks such as not being able to obtain sufficient gain in a specific frequency band and the capacitance of the capacitors forming the circuit becoming large.

SUMMARY OF THE INVENTION An object of the present invention is to provide a wideband amplifier that can achieve sufficient gain over a wide range from low to high frequencies with a simple circuit configuration.

[Means for solving problems]

The wideband amplifier according to the present invention includes a FET as an amplifying element, and connects a plurality of amplifier circuits in parallel that handle different frequency bands, and adjusts at least the gate length of the FET according to the frequency band of the plurality of amplifier circuits. It is characterized by being different.

[Effect]

According to the configuration of the present invention, the gate length of the FET serving as the amplification element of each amplifier circuit is optimized according to the frequency band in charge of the FET.

〔Example〕

Hereinafter, some embodiments of the present invention will be described with reference to the accompanying drawings. In addition, in the description of the drawings, the same elements are given the same reference numerals, and redundant description will be omitted.

FIG. 1 shows the basic configuration of an embodiment of the present invention. As shown in the figure, this broadband amplifier consists of n amplifier circuits 1 1
...1 is connected in parallel to form al' a2
' anru. The input signal is sent to the amplifier circuit 1a□ via the branching circuit 2.

1...1, and these outputs are sent to the multiplexing circuit a
2° an is sent to the output terminal via path 3. Further, a feedback circuit 4 is connected between the output terminal and the input terminal as shown by the dotted line in the figure.

Figure 2 shows the frequency al' of the amplifier circuit 1 1 ... 1
The a2'an band is shown. As shown in the figure, each frequency band is different from each other, and each amplifier circuit 1 1
... Curves a1 to al' a2 showing a gain of 1
'ana are spliced together to exhibit broadband characteristics.

Next, the operation of the broadband amplifier shown in FIG. 1 will be explained.

The input signal includes not only a low-frequency signal but also a middle-frequency or high-frequency signal, and these are separated by frequency by the branching circuit 2. Then, al'a2' is added to the amplifier circuits 1 1 ... 1 in charge of each band.
An sent. Note that this branching circuit 2 can be omitted as long as the input signals of different bands do not affect the input impedance al'a2' an of the amplifier circuits 1 1 ... 1. It is.

At' given to each amplifier circuit 1 1 ... 1
The a2' an input signals of each band are amplified separately. here,
at' in each of the amplifier circuits 1 1 ... 1
The FETs used as a2' an amplification elements differ at least in their gate lengths. That is, the gate length of the amplifier circuit 1a, which handles the low frequency range, is the longest, and the gate length of the amplifier circuit 1, which handles the high frequency range, is the shortest. Therefore, a large gain can be easily achieved even in the low frequency range. Furthermore, the threshold values and gate widths of the FETs are also optimized according to the respective frequency bands. Therefore,
Large gains in each band can be achieved with a simple configuration.

The amplified signals of each band are sent to the multiplexing circuit 3 and multiplexed. Therefore, when viewed as a whole, wideband amplification as shown in FIG. 2 is achieved.

Furthermore, since the wideband amplifier shown in FIG. 1 is provided with a feedback circuit 4 that performs overall feedback, the output signal can be stabilized and the band can be further widened. Note that this feedback circuit 4 is not essential and can be omitted.

Next, a first embodiment of the present invention will be described with reference to FIG.

FIG. 3 is its circuit diagram. This wideband amplifier is constructed by connecting in parallel DC amplifier circuits 1 and 1 that handle low frequencies and AC amplifier circuits 1 and 2 that handle high frequencies. The DC amplification circuits 1, 1 include an amplification FET 11 at the front stage, an FET 12 used as its load, and an amplification FET 13 at the rear stage.
It is composed of diodes 15 and 16 for level shifting the source current (output current) and an FET 14 as a load. Here, the gate lengths of the FETs 11 to 14 are relatively long, about 1 μm, so that a high gain can be easily obtained. Also, short channel effects occur, making it easier to create DC amplifiers.

On the other hand, the DC amplifier circuits 1 and 2 are equipped with an amplifying FET 12.
, a resistor RB for setting a gate bias, a resistor R2 as a load, a capacitor C1 and a resistor R1 connected in series between the drain and gate. Here, the gate length of the FET 12 is relatively short, about 0.5 μm. FET with short gate length has gate capacitance ff1
C is small and high s. Excellent frequency characteristics, but drain conductance gd
tends to be larger than FETs with long gate lengths, and there is an optimal gate length that balances the gain controlled by the value of A-g/gd and the frequency band in which amplification is shared.

On the other hand, the branching circuit 2 is composed of a low-pass filter 2L consisting of two inductors and one capacitor, and a bypass filter 2H consisting of one inductor and two capacitors, and the multiplexing circuit 3 is constructed in the same manner as above. It is composed of a low pass filter 3L and a bypass filter 3H.

According to the first embodiment described above, the low-frequency component of the input signal passes through the low-pass filter 2L and is amplified by the DC amplifier circuit 1aL. Here, various parameters such as the gate length, gate width, and threshold value of the FETs 11 to 14 are optimized to be suitable for low-frequency operation, so that a good amplified output can be obtained. This output is then sent to the output terminal via the low-pass filter 3L. On the other hand, the high frequency component of the input signal passes through the bypass filter 2H and is passed through the AC amplifier circuit 1a2.
is amplified. Here, various parameters of the FET 21 are optimized so that it is suitable for AC operation. In addition, the low frequency cutoff wave number of these amplifier circuits 1 and 2 is C,
Although it is determined by the time constant due to R, (1) Since the low-frequency component is not a problem in this amplifier circuit 'a2, it is possible to reduce the capacitance of the capacitor C1, and therefore to reduce its size itself. This amplifier circuit 1, 2
The amplified output passes through a low-pass filter 3L, is combined with a low frequency component, and is sent to an output terminal.

Next, a second embodiment of the present invention will be described with reference to FIG.

FIG. 4 shows its circuit diagram. In the same figure, amplifier circuit 1
a□ is for low frequency amplification, and the difference from that in Figure 3 is as follows.
Only one level shift diode 15 is provided. Note that the gate length of FETs 11 to 14 is 1.
Since it is approximately 2 μm, the drain conductance gd becomes large, and a large gain can be easily obtained. The amplifier circuit 1a2 is for mid-range amplification, and F as an amplification element,
It is composed of an ET22, a resistor RB2 for setting gate bias, and a resonant load consisting of a capacitor C and an inductor L2. Note that the gate length of FET22 is 0.7μ.
It is about m. The amplifier circuit 1a3 is for high frequency amplification, and is composed of an FET 32 as an amplifying element, a load consisting of an inductor L3, and a resistor RB3 for setting a gate bias. Note that the gate length of FET32 is 0.4 μm.
Therefore, the gate-source capacitance C is small, S, and the high frequency characteristics are excellent.

On the other hand, the branching circuit 2 is composed of a low-pass filter 2L for low-pass, a band-pass filter 2B for middle-pass, and a bypass filter 2H for high-pass. It is composed of a low-pass filter 3L, a band-pass filter 3B, and a low-pass filter 3L.

According to the above embodiment, a low frequency component of about DC to IGH is applied to the amplifier circuit 1al via the low-pass filter 2L, amplified, and sent to the low-pass filter 3L. I.G.
H~2.5GH z
The z-frequency acid component is applied to the amplifier circuit 1a2 via the bandpass filter 2B, amplified, and sent to the bandpass filter 3B. Then, the high frequency component of about 2.50H to 4GH is given to the amplifier circuit 1a3 via the bypass filter 2H, amplified, and sent to the bypass filter 3H. Therefore, each frequency component is amplified by an amplifier circuit optimally designed for each band, multiplexed by a multiplexing circuit 3, and provided to an external circuit as one output signal.

The present invention is not limited to the above embodiments, and various modifications are possible.

For example, the specific amplifier circuits are not limited to those shown in FIGS. 3 and 4. Further, although optimization of the FET gate length has been described in the embodiment, various parameters other than the gate width and threshold value may be optimized. Further, the circuit of the embodiment may be integrated using GaAs or the like.

〔Effect of the invention〕

As explained above in detail, in the present invention, the gate length of the FET serving as the amplification element of each amplifier circuit is optimized according to the frequency band in charge, so that low-frequency Sufficient gain can be achieved over a wide range from low to high frequencies.

[Brief explanation of the drawing]

FIG. 1 is a basic configuration diagram of a wideband amplifier according to an embodiment of the present invention, FIG. 2 is a frequency characteristic diagram thereof, and FIGS. 3 and 4 are circuit diagrams of the first and second embodiments. 1a□~1an...Amplification circuit, 2...Branching circuit, 2
L...Low pass filter, 2B...Band pass filter, 2H...Bypass filter, 3...Mixer circuit, 3L...Low pass filter, 3B...Band pass filter, 3H...Bypass Filter, 4... feedback circuit. Patent applicant: Sumitomo Electric Industries, Ltd.

Claims (1)

[Claims] A plurality of amplifier circuits, each including an FET as an amplifier element and in charge of different frequency bands, are connected in parallel, and at least the gate length of the FET is set in accordance with the frequency band of the plurality of amplifier circuits in charge of the low frequency band. A wideband amplifier characterized by having a long high frequency band and a short high frequency band.