JPS5934705A - Semiconductor integrated circuit - Google Patents

Abstract

PURPOSE:To actuate a semiconductor IC with a low level of current, by cascading three tiers of FETs having small gate width and then applying a negative feedback to the gate of the 1st tier from the drain of the 3rd tier by a resistance. CONSTITUTION:A high-impedance connection is given between FET1 and 2 as well as FETs 2 and 3 with insertion of coupling capacitors 10 and 11 respectively. As a result, the gain of each FET increases. Furthermore the open loop gain can be increased more owing to the three-tier cascade. Thus the open loop gain is increased greatly up to about 60dB when the gate width of the FET is set at each value shown in a table. As a result, it is possible to increase the feedback resistance up to 8OMEGA to obtain the input/output matching. Thus, the overall gain can be increased up to about 30dB.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to semiconductor integrated circuits. The present invention achieves high gain and low power consumption by directly connecting three field effect transistors (hereinafter referred to as FETs) with a coupling capacitor and applying negative feedback from the third stage to the first stage through a resistor. The present invention provides an FET monolithic wideband amplifier with high performance.

Conventional configuration and its problems A negative feedback amplifier in which a resistor is inserted between the drain and gate of FF and T is known as a low noise wideband amplifier. However, in a negative feedback amplifier using a single FET, for example, 20d
In order to make a big profit of B, 7Q, K is FET
It is safe to widen the gate width to about 2 ken.

However, this increases the human power capacity 111 and requires a large operating current.

In a conventional negative feedback amplifier circuit using a single FET, the FET
Even if the gate width is widened, the ob/loop gain cannot be increased very much. For example, in the case of an FET with a gate width of 1 inch, the open loop gain is about 20 dB. Therefore,
The value of the feedback resistor for matching the human output is about 300Ω, and cannot be made large, so the overall gain becomes even smaller. It's a trench, and the return resistance is small, so the NF (noise figure) is also bad. If the gate width is further widened, the transconductance gm is increased, and the feedback resistor is made thicker, the gain will increase, but the operating current will increase, and the gain flatness will worsen due to the increase in human power capacitance. becomes narrower.

A first aspect of the present invention is to eliminate the above-mentioned drawbacks of the conventional art, and an object of the present invention is to provide a semiconductor integrated circuit of a high gain broadband amplifier that operates with low current.

Structure of the Invention The present invention connects FETs with small gate widths in three stages,
By applying negative feedback from the drain of the third stage to the gate of the first stage using a resistor, a high gain broadband amplifier that operates with low current can be made to have -iJ performance.

Description of examples Hereinafter, the present invention will be explained based on Examples.

FIG. 1 is a circuit diagram of a semiconductor integrated circuit according to an embodiment of the present invention. 1, 2.3 are GaAsFETs, 4 is an input terminal, and 6 is an output terminal.

6.7 is a drain bias terminal, 8.9 is a gate bias terminal, and 10.11 is a coupling capacitor. 12.1
3 are a feedback capacitance and a feedback resistance, respectively.

In this circuit, only coupling capacitors 10 and 11 are inserted between FETs 1, 2, and 3, respectively, for high impedance coupling, so the gain of each FET is large, and the oscilloscope loop gain is large due to the three-stage connection. can be made even larger. The gate width of the FET used in the example of the present invention is
400μm for FET1, 200μm for FET2 and 3
It is.

The following table shows the values of each element in this example.

In this case, the open loop gain can be as large as approximately 60 dB. Therefore, the feedback resistance for input/output matching is also very high at 8Ω. As a result, the overall gain increases to about 30 dB.

FIGS. 2 and 3 compare and show the results of dividing the S parameters of a negative feedback amplifier circuit using a single FET and an amplifier circuit according to an embodiment of the present invention. 14 is a characteristic curve of ls211 of the amplifier circuit according to the embodiment of the present invention, and 15 is a characteristic curve of ls211 of a negative feedback amplifier circuit using a single FET. 4 from characteristic curve 14
．． The reason why the value of 1s2i is small on the low frequency side as shown in the figure is due to the influence of the coupling capacitor inserted between each FET, but the flatness of 15211 is improved.

In FIG. 3, 16 and 17 are single-FETs, respectively.
The characteristic curve of IS 221 of the negative feedback amplifier circuit according to
18 and 19 indicate the characteristic curves of ls++l and ls221, respectively, of the amplifier circuit of the embodiment of the present invention.

Further, FIG. 4 shows the gain and NF frequency characteristics of a GaAs monolithic IC broadband amplifier using this circuit.

In the figure, 20 represents the gain frequency characteristic curve, and 21
respectively show the curves of the frequency characteristics of the NF.

The values of each element are the same as those shown in the previous example.

Approximately 28 in the 60-100100O band as shown in Figure 4
A flat gain characteristic of dB is obtained.

On the other hand, NF has a high feedback resistance of 50 to 1000
1'1 of less than 2.3 dB has been obtained in the MHz band.The drain voltage is 3V and the operating current is 25mA, compared to the operating current of 30mA in a conventional amplifier using an FET with a gate width of 100μm. , is reduced by about 20%. In the above embodiment, the case where a feedback capacitor is inserted has been explained, but this feedback capacitor does not need to be inserted. The gate width of the FET is 400 μm.

I explained the case of 200μm, 200μm, but in order to have low distortion characteristics, the gate width of each stage FET is 100μm.
, 200 μm, and 300 μm, similar effects can be expected.

Effects of the Invention As described above, the semiconductor integrated circuit of the present invention reduces power consumption by directly connecting three stages of FETs through coupling capacitors and applying negative feedback from the drain of the third stage to the gate of the first stage using a resistor. This makes it possible to produce a small, high-gain, low-noise, wideband amplifier, and has high industrial value.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a semiconductor integrated circuit according to an embodiment of the present invention, and FIGS. 2 and 3 are calculation results of S parameters of a circuit according to an embodiment of the present invention and a conventional negative feedback amplifier circuit using a single FET. The figure shown in Figure 4 is a diagram showing the gain and NF frequency characteristics of a circuit according to an actual sister example of the present invention. 1...First stage FET, 2...Second stage FE
T, 3...Three stages IJ F E T, 4...
...Input terminal, 5...Output terminal, 6.7...
・Train bias terminal, 8, 9...Kate bias terminal, 10.11・Mountain...Coupling capacitor, 12
...Feedback capacitance, 13...Feedback resistance, 1
4... Calculation result of 1s211 of the circuit of the present invention, 1
5...1s21 of negative feedback circuit using single-FET
1 calculation result curve, 16.17 ... Single-FE
Curve of the calculation result of ls++l, 1s221 of the negative feedback circuit by T, 18.19... 1 of the circuit of this example
8111, 1s771 calculation result curve, 20...Curve of the frequency characteristic of the gain of the circuit of the embodiment of the present invention, 21.
...Curve of frequency characteristics of NF of the same circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2: MHir Figure 3: J Soju CNHz Figure 4: M 5 gray 1 arrow (hjHi)

Claims (2)

[Claims] (1) A semiconductor characterized in that three field effect transistors are coupled in three stages via a coupling capacitor, and a resistor is inserted between the drain of the field effect transistor in the third stage and the gate of the first stage field effect transistor. integrated circuit. (2) The semiconductor integrated circuit according to claim 1, wherein a container is inserted in series with the resistor.