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Feedback-based broadband low-noise amplifier

In Electronic Infomation Category: F | on April 20,2011

Low noise amplifier in communications, radar, electronic countermeasures, and HY628100ALLG-70 datasheet and remote telemetry system of the essential and HY628100ALLG-70 price and vital parts, it is located in the RF front-end receiving system, the main feature is the weak RF antenna receives a linear signal amplification, while suppressing all kinds of noise interference and HY628100ALLG-70 suppliers and increase system sensitivity. Especially with the communications, electronic warfare, microwave measurement toward broadband, low noise, small size direction, low noise and broadband amplifier design problem has been more and more extensive attention. This gives a 50 ~ 300 MHz low-noise broadband amplifier, the amplifier has an excellent working band gain flatness and noise figure, can improve receiver sensitivity.

1 broadband implementation and principle of negative feedback

Broadband amplifier design of the main obstacles to active device gain-bandwidth product of the constraints, that is, the gain of active devices in the frequency of high-end as the frequency increased to 6 dB / octave down. Broadband amplifier design method commonly used are: balanced structure amplifier, negative feedback amplifier, active matching circuits, reactance matching network, broadband resistive match, distributed amplifiers. Negative feedback amplifier, which has the following obvious advantages: reduced performance of the circuit sensitivity to changes in the transistor itself; get better input impedance matching and low noise figure; increase the stability of the amplifier within the frequency band; increase the amplifier linearity. Therefore, the negative feedback technique is widely used in broadband amplifier designs.

Amplifier using negative feedback shown in Figure 1.

Figure 1 negative feedback amplifier

Between gate and drain of which the feedback network consists of capacitors, resistors and inductors composition. One role is to prevent the feedback capacitance of the transistors DC bias network impact; inductance is to reduce the frequency of high-end amplifier in the feedback, the gain of the amplifier offset decreases with increasing frequency, by adjusting the size of the inductor can adjust the amplifier gain flatness. Play a major role in the feedback resistance, resistance by regulating the size of the amount of feedback can be adjusted. At the same time when the feedback resistor, the amplifier can get a good impedance matching.

2 bias circuit and the stability factor of

2.1 Bias Circuit

Amplifier bias circuit shown in Figure 2. Figure 2, the inductor L1 and L2 is the RF choke (RFC); capacitors C1-C4 for the power supply filter capacitor; R3 by the formula (1) push:


which is leakage current, BB I is the current flowing through the R1/R2 voltage divider network. R1 and R2 by equation (2) and (3) push:

Figure 2, the amplifiers bias circuitry

2.2 stability factor

Stability of the circuit design is essential, relatively easy because of the high gain amplifier self-excitation. Consider the stability of the amplifier is the main consideration when stability factor K and | |, in order to get absolute stability of the network, you must meet the K> 1 and | |

Stability factor K and | | expressions such as (4) and (5) shows:

When the above two conditions are simultaneously met, the amplifier is absolutely stable; If these two conditions can not be met, the amplifier will potentially unstable and oscillation. At this point need to take some measures to improve the stability of the amplifier, the main methods are: source series of negative feedback; drain and gate parallel negative feedback; drain series resistance and drain resistance in parallel; into the ferrite isolators.

3 ADS simulation and circuit test

ATF54143 provided under the Avago transistor model, created in ADS circuit design low-noise amplifier noise figure and S-parameter simulation and optimization. Making process taking into account the potential errors in the design performance simulation, the required settings must be higher than the performance indicators. Through repeated optimization, the resulting simulation results are as follows: in the 50 ~ 300 MHz band, a gain of 23 0.2 dB, noise figure less than 0.4, the input VSWR less than 1.4, output VSWR is less than 1.4.

According to the simulation results, making PCB boards, the assembly of the amplifier, shown in Figure 3.

Then use the Agilent E5061A network analyzer and N8975 Noise Figure Analyzer to test the amplifier, gain, VSWR and noise figure of the test results are shown in Figure 4, Figure 5 and Figure 6.

physical map in Figure 3 amplifier

Figure 4 Gain versus frequency

Figure 5 Input / Output VSWR versus frequency

Figure 6, the relationship between noise and frequency

From Figure 4, Figure 5 and Figure 6 shows the development of broadband low-noise amplifier (50 ~ 300 MHz) the work of the band, the gain is greater than 22 dB, flatness is less than 0.3 dB, noise figure less than 1.25, the input VSWR less than 1.4, the output VSWR less than 1.3. Low-noise amplifier can be seen that the test results agree well with the simulation results. But the test results of noise figure slightly lower than the simulation, the gain was slightly lower than the simulation results, this is due to capacitance, the parasitic resistance of the inductor, while debugging the filter input port and output port is not an exact match, the device is not a ground of well, and testing of cables and connectors.

4 Conclusion

Broadband low noise amplifier is an indispensable communication device, here by a negative feedback, the choice of Avagos high-electron mobility transistor ATF54143 designed a low-noise broadband amplifier, and microwave simulation software to optimize ADS obtained work in the 50-300MHz frequency band, the gain is greater than 22 dB, flatness is less than 0.3 dB, noise figure of less than 1.25, the input VSWR less than 1.4, the input VSWR less than 1.3.

The innovation here is the use of negative feedback techniques to design low-noise broadband amplifier, the amplifier has high gain, gain flatness and excellent, and noise etc, and can be widely used in microwave communications, satellite communications and other electronic device.

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