SWRA004A
Low-Band LNA
In a typical down-conversion receiver, the LNA is usually placed directly after the antenna and a band-select filter. The purpose of the LNA is to amplify the desired signal being received while adding as little undesired noise and distortion as possible. The TRF1500 LNA is a common emitter amplifier, designed to operate on a single 3.75 volt supply. The LNA has two selectable gain states, normal state or strong signal state, which are controlled with the digital CMOS control lines. The strong signal state, which disables the LNA, is provided for operation in a high signal environment such as near the base station. Operating near the base station in the normal state could cause an increase in the intermodulation product levels and thus cause undesired noise and distortion in the receiver. Stand-alone LNA performance can be ascertained by reconfiguring the evaluation board as noted on the datasheet.
Low-Band LNA Turn on Time
The turn on time can be adjusted by changing the values of C10, R6 and R7, as shown in Figure 3 and Figure 4. The resistors form a voltage-divider network across the supply, Vcc. The function of this network is to provide a bias condition near the ideal operating region at the base of the common emitter amplifier. By providing this bias condition, the charge time of the series capacitor, C10, can be adjusted. Changing the value of resistors should not affect gain, IIP3 or noise figure (NF) performance.
Figure 3. Voltage Divider at Low-Band LNA Input
TRF1500 Integrated Dual-Band RF Receiver User’s Guide | 19 |
