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INA-30311 Datasheet(PDF) 5 Page - Agilent(Hewlett-Packard) |
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INA-30311 Datasheet(HTML) 5 Page - Agilent(Hewlett-Packard) |
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5 / 6 page 
6-144 RF OUTPUT RF INPUT VCC Figure 13. Basic Amplifier Application. 900 MHz Matched Example This section describes a demonstration circuit for 900 MHz that is based on the matched output configuration shown in Figure 11. The output VSWR of the INA- 30311 is approximately 2.6:1 at 900 MHz and results in a 0.9 dB mismatch loss when used in a 50 Ω system. The use of a simple impedance matching circuit at the output will increase both gain and output power by 0.9 dB. The noise figure of the amplifier remains the same and does not depend on whether or not the output is matched. There are many circuit topologies that may be used to match the output impedance of the INA-30311 to a 50 Ω load. The example presented in Figure 15 is designed to match the amplifier’s output for frequencies near 900 MHz. This circuit is representative for applications in the 800 MHz cellular or 900 MHz unregulated frequency bands. This example uses a series capacitor to resonate with a shunt, high impedance transmission line. The transmis- sion line is tapped at a 50 Ω level for the output. This circuit provides the desired impedance transformation with a minimum of components, using only one chip capacitor that also doubles as the output DC block. used to the amplifier to the VCC supply, additional bypass capacitors may be needed to prevent resonances that would otherwise result in undesirable gain responses. A well-bypassed VCC line is also desirable to prevent possible oscillations that may occur due to feedback through the bias line from other stages in a cascade. Adequate grounding is needed to obtain maximum performance. The ground pin of the INA-30311 should be connected to directly to RF ground by using plated through holes (vias) near the package terminals. FR-4 or G-10 PCB material is a good choice for most low cost wireless applications. Typical board thickness is 0.025 or 0.031 inches. The width of 50 Ω microstriplines in these PCB thicknesses is also convenient for mounting chip components such as the series DC blocking capacitors. 50 Ω Example The demonstration circuit in Figure 14 shows the INA-30311 used without output impedance matching and is an example of the cascade depicted in Figure 12. This layout illustrates the simplest implementation of the INA-30311 by using 50 Ω microstriplines with DC blocking capacitors for both the input and output. The VCC supply connection is RF bypassed very close to the lead of the RFIC. Provision is also made for an additional bypass capacitor on the VCC line near the edge of the PCB. Operating Details The basic application of the INA- 30311 is shown in Figure 13. DC blocking capacitors should be placed in series with the RF Input and RF Output to isolate adjoin- ing circuits from the internal bias voltages that are present at these terminals. The values of the blocking capacitors are deter- mined by the lowest frequency of operation for a particular applica- tion. The capacitor’s reactances are chosen to be 5% or less of the amplifier’s input or output imped- ance at the lowest operating frequency. For example, an ampli- fier to be used in an application covering the 902 to 928 MHz band would require an input blocking capacitor of at least 70 pF, which is 2.5 Ω of reactance, or 5% of 50 Ωat902 MHz. The VCC connection to the amplifier must be RF bypassed by placing a capacitor to ground directly at the bias pin of the package. Like the DC blocking capacitors, the value of the VCC bypass capacitor is determined by the lowest operating frequency for the ampli- fier. This value is typically the same as that of the DC blocking capacitors. If long bias lines are |
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