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# ADS simulation-based design of low noise amplifier

1 Introduction

Low-noise amplifier (LNA) in RF receiver front-end, its main function is to amplify weak signals to low noise. In the low-noise amplifier design process, think of their amplification, noise figure and PIC16F84A-04/P datasheet and matching and PIC16F84A-04/P price and other factors, which requires a large number of theoretical calculations and PIC16F84A-04/P suppliers and smith chart analysis, to design difficult.

Advanced Design System (ADS) software is the Agilent EDA software company in HPEESOF series developed on the basis of a comprehensive design software, containing many small-signal amplifier design controls, to achieve a large number of calculations and smith chart analysis. The following describes how to use the ADS design and simulation of low-noise amplifier.

2 low-noise amplifier design theory

Figure 1 is a block diagram of the amplifier circuit, which said the source reflection coefficient r, r that the load reflection coefficient. Different r and r. . Will affect the stability of the amplifier, noise figure, gain, VSWR and other parameters. Amplifier design process is based on s-parameters of the amplifier, and noise figure, gain, VSWR and other requirements to determine TS and TL, TS and the TL and then determine the input and output matching networks.

transistor amplifier circuit in Figure 1 Block diagram

Key indicator is the low noise amplifier noise figure Ts, its relationship with the source reflection coefficient is as follows:

Which NFmin and Rn are the minimum transistor noise figure and noise resistance, etc., Topt is the optimum source reflection coefficient. When Ts = Topt, you can obtain the minimum noise figure NFmin.

General low-noise amplifier input matching circuit is designed in accordance with the best noise, in order to obtain higher gain and better power output VSWR, output by the output conjugate match.

3 low-noise amplifier design simulation and optimization

3.1 Design Goals

Low-noise amplifier circuit design is the key to the first level. For low-noise amplifier circuit of the second level and follow-up, you can use to complete the MMIC microwave monolithic amplifier, its design is relatively simple.

33,143 to complete the circuit by ATF of a first-class design goals are: Frequency: 1260MHz a 1280MHz; gain: 10dB; Noise Figure: 0.5dB; Input VSWR: 1.5; output standing wave ratio : 1.5.

3.2 Simulation Design

a 33143 device manual, the device provides a standard model Manual J.

(2) determine the operating point and the bias circuit

According to the DC operating point of the chip in the performance choice under the conditions of the DC operating point. This article was selected DC operating point: VDS: 4V, IDS = 40mA. DC operating point of the chip under the minimum noise figure F i = 0.34dB.

(3) stability of the judge

In the ADS software, according to Mu Mu-Prime controls and controls to determine the stability of the circuit. Circuit is necessary and sufficient conditions for absolute stability is the Mu> 1 and Mu-Prime> 1.

General measures to improve the stability of:

A. Series resistance of the negative feedback

In FET in series between the source and to a resistance component, which constitutes a negative feedback circuit. Feedback element used in place of a microstrip line, which is equivalent to negative feedback inductive components.

B. Stability attenuator

P-type resistive attenuator is a simple and feasible measures to improve the stability of the amplifier, usually low-noise amplifier connected to the final output port.

Measures taken to improve the stability: on-chip inductance source added negative feedback; LRC series circuit add in the drain. Figure 2 shows the stability after adding the feedback circuit simulation results. 0.7GHz ~ 3GHz frequency circuit is absolutely stable state, and a frequency of 1260MHz 1280MHz, so to meet the stability requirements.

Figure 2, the improved stability of the simulation results

(4) Design of input and output matching circuits

First round and by other factors such as noise, gain circles to set a reasonable source reflection coefficient r, then according to the source reflection coefficient r and s parameters of the amplifier, in accordance with the maximum gain matching to determine the load reflection coefficient is greater than 10dB gain and under Tl 0.5dB noise figure less than the design goal, as shown in Figure 3, settings such as noise figure and gain circles round controls control.

Figure 3 and other such noise figure and gain circles round controls control

Figure 4 is a circle and so on and so gain the noise figure circles to Smith chart representation of the simulation results. Select the source reflection coefficient points in the noise figure, gain a compromise between these two indicators, select m1 point source reflection coefficient points. m1 point source reflection coefficient of the corresponding noise figure is less than 0.3, a gain of 11dB.

Determine the source reflection coefficient, according to the formula:

Calculate the load reflection coefficient Tl, and then use Smith original design input and output matching circuits.

Figure 4, noise figure circles, such as gain and input match point circles determined

(5) optimization

In the above, the design of the DC bias circuit, respectively, and input and output matching network, but the input and output matching networks will change the addition of S-parameters of FET, which worsened in some indicators. In order to meet all the design goals, it is necessary to optimize the overall circuit. First select the optimal variables, set variables range, and then set the simulated target design goals, optimizing simulation variables, get the default target to achieve the best circuit design parameters. The optimized simulation results shown in Figure 5.

Figure 5, the optimized simulation results

4 Conclusion

By the simulation results, the low noise amplifier designed in the band 1260Mhz ~ 1280MHz work, the gain is about l1dB, input and output VSWR less than 1.5, the noise figure of about 0.2dB, at 1 GHz the absolute frequency range of a stable 3Ghz, all indicators meet the design requirements. The design for the design of low noise amplifier has a certain reference value.

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