Radio frequency transceiver front end circuit with direct current bias switch
A front end circuit for coupling an antenna to a radio frequency (RF) transceiver for time domain duplex systems is disclosed. The front end circuit includes an antenna port, a power amplifier, a low noise amplifier, and a matching network. The output of the power amplifier and the input of the low noise amplifier are coupled to the matching network and connected in common to the antenna. The power amplifier and the low noise amplifier are activated and deactivated in sequence corresponding to the transmit and receive modes of the transceiver, and the matching network minimizes the effect that one has on the other at the designated operating frequency.
1. A radio frequency (RF) transceiver front end circuit with a predefined operating frequency for connecting a transceiver to an antenna, the front end circuit comprising:
an antenna port connectible to the antenna;
a transmit port;
a receive port;
a power amplifier including a first power amplifier transistor having a base coupled to the transmit port, a collector, and an emitter;
a power amplifier input matching network coupling the transmit port and the base of the first power amplifier transistor;
a power amplifier control circuit with a first adjustable voltage source coupled to the base of the first power amplifier transistor, the power amplifier control circuit activating and setting a bias point of the first power amplifier transistor;
a low noise amplifier including a first low noise amplifier transistor having a base, a collector coupled to the receive port, and an emitter;
a low noise amplifier output matching network coupling the receive port and the collector of the first low noise amplifier transistor;
a low noise amplifier control circuit with a second adjustable voltage source coupled to the base of the first low noise amplifier transistor, the low noise amplifier control circuit activating and setting a bias point of the first low noise amplifier transistor;
a direct current bias switch coupled to the low noise amplifier and activated by the low noise amplifier control circuit; and
a matching circuit including a power amplifier output matching segment coupled to the collector of the first power amplifier transistor and the antenna port, and a low noise amplifier input matching segment coupled to the base of the first low noise amplifier transistor and the antenna port, the power amplifier matching segment having shared components with the low noise amplifier segment.
2. The front end circuit of claim 1 , wherein the direct current bias switch is activated together with the low noise amplifier.
3. The front end circuit of claim 1 , wherein the direct current bias switch includes a switching transistor having a collector, a base coupled to the low noise amplifier control circuit, and an emitter coupled to the collector of the first low noise amplifier transistor via a component of the low noise amplifier output matching network.
4. The front end circuit of claim 3 , further comprising:
a low noise amplifier bias voltage source coupled to the collector of the switching transistor.
5. The front end circuit of claim 3 , wherein the low noise amplifier output matching circuit network is coupled to the collector of the first low noise amplifier.
6. The front end circuit of claim 3 , further comprising:
a bias settling resistor coupling the base of the switching transistor to the low noise amplifier control circuit.
7. The front end circuit of claim 1 , wherein the low noise amplifier control circuit further includes a resistive divider having a resistance value greater than an activated base-emitter resistance of the first low noise amplifier transistor.
8. The front end circuit of claim 1 , wherein the first transistor of the low noise amplifier has a common-emitter configuration.
9. The front end circuit of claim 1 , further comprising:
a degeneration inductor coupled to the emitter of the first low noise amplifier transistor and ground.
10. The front end circuit of claim 1 , wherein the power amplifier, the low noise amplifier, and the matching network are fabricated on a single die of silicon substrate.
11. The front end circuit of claim 1 , wherein the power amplifier, the low noise amplifier, and the matching network are fabricated on a single die of gallium arsenide (GaAs) substrate.
12. The front end circuit of claim 1 , wherein the power amplifier, the low noise amplifier, and the matching network are each discrete, interconnected components.