基于atf54143的低噪放LNA的设计100M-500M(2)

Input and output RF connectors are EF Johnson end-launch

SMA connectors (p.n. 142-0701-881).The numbers associated with the chip capacitors and re-sistors refer to the dimensions of the components: 0402 = 40 x 20 mil, etc.

100M-500M低噪放设计方案

Thus, by forcing the emitter voltage (VE) of transistor Q1 equal to Vds, this circuit regulates the drain current in a manner similar to a current mirror. As long as Q2 oper-ates in the forward active mode, this holds true. In other words, the collector-base junction of Q2 must be kept reverse biased.

An evaluation board was designed for the feedback ampli-fier network. This single-layer board (see Figures 4 and 5) is 0.031-inch thickness FR-4 material with a dielectric constant of 4.2. The feedback network should be made as short as possible, since introducing inductance into the feedback network causes instability in the 5-6 GHz region. The RC feedback uses 40 x 20 mil components that are soldered close together with a small solder pad in between.

The ATF-54143 is conditionally stable below 3.5 GHz, having 29-26 dB gain in the 100-500 MHz region. The RC feedback reduces low frequency gain and increases the stability factor to >1 below 2 GHz. The amplifier uses a high-pass impedance matching network, consisting of C1 and L1, for the noise match. The circuit loss will directly relate to noise figure, thus the Q of L1 is extremely important. The Toko LL1608-FSR15 is a small multi-layer chip inductor with a rated Q of 19 at 50 MHz. The shunt inductor (L1) provides low frequency gain reduction, which can minimize the amplifier’s susceptibility to overload from nearby low frequency transmitters. It is also part of the input match-ing network along with C1. C1 also doubles as a DC block, while L1 also provides a means of inserting gate voltage for the PHEMT. This requires a good bypass capacitor in the form of C2.

Figure 4. RF Layout for Demo Board.

Figure 5. Assembly Drawing for Amplifier.

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100M-500M低噪放设计方案

This network represents a compromise between noise figure, input return loss, and gain. Capacitors C2 and C5 provide in-band stability, while resistors R5 and R7 provide low-frequency stability by providing a resistive termina-tion. The high-pass network on the output consists of a series capacitor C4 and shunt inductors L2, with L2 also providing a means of inserting drain voltage for biasing up the PHEMT. Very short transmission lines between each source lead and ground have been used. The RC feedback has a dramatic effect on in-band and out-of-band gain, stability, and input and output return loss.

Simulated vs. Actual Performance of the E-pHEMT Broadband LNAResults from the simulation of gain, NF, and for input and output return loss are shown in Figures 6 and 7, respectively. Measured gain and noise figure and input and output return loss appear in Figures 8 and 9, respectively. A summary of the measured results is shown in Table 2.

Figure 6. Simulation Results for Gain and Noise Figure.

Figure 7. Simulation Results for Input and Output Return Loss.

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100M-500M低噪放设计方案

Table 2. Measured Results.Frequency (MHz) 100 200 300 400 500

Gain (dB) 20.8 21.1 21.4 21.2 20.5

NF (dB) 1.20 0.67 0.62 0.61 0.70

P1dB (dBm) +16.6 +16.6 +16.6 +16.6 +16.8

OIP3 (dBm)+34.5+36.3+36.5+36.1+36.5

Figure 8. Measured Results for Gain and Noise Figure.

Figure 9. Measured Results for Input and Output Return Loss.

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100M-500M低噪放设计方案

References

[1] Ward, A. J. “Applications Note AN-1222: A Low Noise

High Intercept Point Amplifier for 1930 to 1990 MHz using the ATF-54143 PHEMT.”

[2] Maas, Stephan. Nonlinear Microwave Circuits. IEEE Press,

New York, 1997.

[3] Curtice, W. R. “A MESFET model for use in the design of

GaAs integrated circuits.Tech. May 1980, Vol. MTT-28, pp. 448-456. ” IEEE Trans Microwave Theory Avago Eesof Advanced Design System (ADS) electronic design automation (EDA) software for system, RF, and DSP designers who develop communications products. More information about Avago Technologies’ EDA software may be found on /eesof-eda.Performance data for Avago Technologies’ ATF-54143 may be found on /view/rf

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