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A 5 W MMIC Driver Amplifier for PCS Base Stations
Today’s wireless telecommunications equipment demands high performance, low cost components that are readily available and easy to implement. The model RMPA1911-96 GaAs power amplifier is a high efficiency, 5 W unit supplied in a metal-based in-line package for use as a driver stage for personal communications service (PCS) base stations. The amplifier features a two-stage design that includes input and output matching and bias circuitry, and is designed as a single-ended configuration with shunt feedback and harmonic tuning for increased power-added efficiency (PAE). The design utilizes the company’s 0.5 mm power pseudomorphic high electron mobility transistor (PHEMT) process.
The amplifier employs discrete PHEMTs and surface-mount components mounted on a softboard substrate. The fabrication technique is compatible with existing surface-mount technology to ensure low cost. In addition, a metal base aids in thermal dissipation and mounting. Edge connectors are used for the RF and DC connections to facilitate assembly.
The amplifier utilizes a mini-hybrid design approach. Matching and biasing are accomplished using surface-mount components, which have higher Qs than equivalent components, thereby achieving a better match and, ultimately, higher PAE.
The unit is designed to operate over the 1930 to 1990 MHz frequency range and typically produces +37 dBm saturated output power. Figure 1 shows the amplifier’s output power and PAE as a function of input power at 1.90 and 1.95 MHz. Typical small-signal gain is 27 dB and noise figure is 4.5 dB (typ) and 6.0 dB (max). Figure 2 shows the device’s small-signal gain vs. frequency.
Typical 50 W input and output return losses are 14 and 16 dB, respectively. The amplifier’s input and output return loss vs. frequency is shown in Figure 3 . Adjacent-channel power ratio (ACPR) is better than –44 dBc at 1.23 MHz offset. Figure 4 shows ACPR plots for ±1.23 MHz offset as a function of output power at 1.9 GHz measured in a 30 kHz bandwidth.
The unit operates from a +8 V DC drain supply and –3.5 V DC gate bias. Total drain current (for both PHEMT devices) is 1000 mA (typ) and the combined gate current is 4 mA. The operating temperature range is specified at –30° to +80°C.
The RMPA1911-96 power amplifier can be utilized in fixed-access or PCS base stations and wireless local loop applications. In addition, the amplifier can be used both as a final output stage or driver stage for higher power amplifiers when high linearity is required. The device is easy to implement due to its small size and the inclusion of the input and output matching circuitry within the surface-mount package. Additional information is available at the company’s Web site at http://www.raytheon.com/micro.
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