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DEMO-MGA-85A Datasheet(PDF) 7 Page - Broadcom Corporation. |
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DEMO-MGA-85A Datasheet(HTML) 7 Page - Broadcom Corporation. |
7 / 13 page 7 MGA-85563 Applications Information Description The MGA-85563 is a two-stage, low noise GaAs RFIC am- plifier designed for receiver applications in the 800 MHz to 5.8 GHz frequency range. The device combines low noise performance with high linearity to make it a desir- able choice for receiver front end stages. A special feature of the MGA-85563 is the ability to cus- tomize its output power capability for higher linearity by setting the device’s current. For applications requiring additional dynamic range, the third order intercept point can be boosted by up to 6 dB by using this feature. The MGA-85563 operates from a +3-volt power supply and draws a nominal current of 15 mA. The RFIC is con- tained in a miniature SOT-363 (SC-70) package to mini- mize printed circuit board space. The combination of 3-volt operation and small size are important to design- ers of miniature, battery-powered wireless communica- tions products such as cellular telephones, PCS, and RF modems. The high frequency response of the MGA-85563 extends through 6 GHz making it an excellent choice for use in 5 GHz RLL as well as 2.4 and 5.7 GHz spread spectrum and ISM/license-free band applications. Internal, on-chip capacitors limit the low end frequency response to applications above approximately 500 MHz. Application Guidelines The MGA-85563 is very easy to use. For most applications, all that is required to operate the MGA-85563 is to apply +3 volts to the RF Output pin, and noise match the RF Input. RF Input To achieve lowest noise figure performance, the input of the MGA-85563 should be matched from the system impedance (typically 50 Ω) to the optimum source im- pedance for minimum noise, *opt. Since the real part of the input of the device impedance is near 50 Ω and the reactive part is capacitive, a simple series inductor at the input is often all that is needed to provide a suitable noise match for many applications. RF Output The RF Output port is internally matched to 50 Ω and will not normally require additional matching. DC Bias DC bias is applied to the MGA-85563 through the RF Output connection. Figure 15 shows how an inductor (RFC) is used to isolate the RF signal from the DC supply. The bias line is capacitively bypassed to keep RF from the DC supply lines and prevent resonant dips or peaks in the response of the amplifier. The DC schematic for an MGA-85563 amplifier circuit is shown in Figure 15. RF Output RFC C3 RF Input C2 +3V C1 Rb Figure 15. Schematic Diagram with Bias and Current Setting Connections. A DC blocking capacitor (C2) is used at the output of the RFIC to isolate the supply voltage from succeeding circuits. While the RF input terminal of the MGA-85563 is at DC ground potential, it should not be used as a current sink. If the input is connected directly to a preceding stage that has a DC voltage present, a blocking capacitor (C1) should be used. Setting the Bias Current for Higher Linearity The MGA-85563 has a feature that allows the user to place an external resistor (Rb) from the Rbias pin to DC ground and thereby increase the device current. The current can be raised from its nominal 15 mA up to ap- proximately 50 mA. The higher current increases ampli- fier linearity by boosting output power (P1dB) by up to 8 dB. Maximum linearity performance is obtained at a current of 30 to 35 mA. Currents greater than 35 mA are not recommended since the output power has reached a point of diminishing returns at this current. Figure 16 shows the relationship between device current and the value of the external resistor. 10 15 20 25 35 30 10 50 90 130 170 200 Rb () Figure 16. Bias Current vs. Resistor Value. |
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