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Pasternack Blog

Bi-Directional Amplifiers -Just the Facts

A Bi-Directional amplifier (BDA) is a device that locates a wireless signal, amplifies it, and then rebroadcasts it throughout a building or area.

The backbone of most range or signal extending technologies is a relatively simple dual amplifier device with an integrated low noise amplifier (LNA) and power amplifier (PA). The Bi-Directional amplifier either enables a weak incoming signal to be amplified and retransmitted to extend its signal, in both directions, or can be used to either transmit a signal from a radio and pre-amplify received signals using the same antenna.

 

 

A simple switched Bi-Directional amplifier topology with a bandpass filter in the receive signal chain can be used as a half-duplex repeater with the transmit/receive control circuitry.

Importantly, there are two main types of Bi-Directional amplifiers, full-duplex and half-duplex. The term, duplex, implies that a device is capable of both transmission and reception simultaneously. Hence, half-duplex implies that the device can perform both transmission and reception, just not simultaneously.

Typically with Bi-Directional amplifiers, the transmission and reception function are selected with switch networks at the ports, or by the use of intelligent biasing. Different methods of switching or biasing could cause transient impedance scenarios, loading of the transmitter PA, or overloading of the receiver LNA if not properly configured or timed. These directions should be detailed in the device’s data sheet as switching time, or with a manufacturer provided control sequence diagram.

On the other hand, full-duplex Bi-Directional amplifiers can perform both reception and transmission, simultaneously. This is often enabled by having a separate transmit and receive frequency—as seen in many cellular and satellite communication technologies, or frequency division multiplexing (FDM). With this topology, duplex filters are used to attenuate the transmit signal in the receive signal chain.