Wideband active balun LNA topology with narrow-band filtering and noise cancelling
The present invention provides a wideband active balun LNA topology with narrow-band filtering and noise cancelling. The amplifier includes three transconductance stages, a feedback network, and a load. The first and second transconductance stages are connected in parallel to receive the input signal. The differential output of the first transconductance stage is fed back to voltage input through a differential-to-single-end-end feedback network, while the output of the first transconductance, passing through the third transconductance, is added to the output of the second transconductance stage in proper phase. The present invention accomplish both wideband low-noise amplification and narrow-band filtering without inserting interface stages, thereby improving the linearity and noise performance of the whole circuit. Noise cancellation technique is implemented in differential way to ensure the low noise figure. The present invention also achieves single-end to differential conversion with balanced output and superior second order linearity performance.
1. A wideband active Balun low-noise amplifier topology comprises: a first transconductance stage, a second transconductance stage, a third transconductance stage, a feedback network, and a first load; wherein
the first transconductance stage is in parallel to the second transconductance stage, a single-end input of the first transconductance stage connects to a voltage input, a first output of the first transconductance stage connects to a first input of the third transconductance stage, and a second output of the first transconductance stage connects to a second input of the third transconductance stage; a single-end input of the second transconductance stage connects to the voltage input, a first output of the second transconductance stage connects to a first output of the third transconductance stage, a second output of the second transconductance stage connects to a second output of the third transconductance stage; the first transconductance stage and the second transconductance stage are used to input voltages;
an output of the feedback network connects to the voltage input, a first input of the feedback network connects to the second output of the first transconductance stage, a second input of the feedback network connects to the first output of the first transconductance stage; and the feedback network is used to convert differential output signal of the first transconductance stage into a single-end signal, and feeds it back to the single-end voltage input to form a feedback loop;
the first input of the third transconductance stage connects to the first output of the first transconductance stage, the second input of the third transconductance stage connects to the second output of the first transconductance stage, the first output of the third transconductance stage connects to the first output of the second transconductance stage, the second output of the third transconductance stage connects to the second output of the second transconductance stage; and the third transconductance stage is used to convert a voltage output by the first transconductance stage into a current, and this current will be added to the a current output by the second transconductance stage; and
one end of the first load connects to the first output of the third transconductance stage, another end of the first load connects to the second output of the third transconductance stage; and the first load is used to receive the summed current from the third transconductance stage and the second transconductance stage, and generate a narrow-band differential voltage signal.
2. The wideband active Balun low-noise amplifier topology according to claim 1 , wherein the feedback network comprises a second load, a feedback resistor, and a feedback amplifier.
3. The wideband active Balun low-noise amplifier topology according to claim 2 , wherein one end of the feedback resistor connects to the voltage input, and another end of the feedback resistor connects to an output of the feedback amplifier.
4. The wideband active Balun low-noise amplifier topology according to claim 2 , wherein a first input of the feedback amplifier connects to one end of the second load, and a second input of the feedback amplifier connects to another end of the second load.
5. The wideband active Balun low-noise amplifier topology according to claim 2 , wherein a voltage signal generated on the second load by the first transconductance stage feeds back to the voltage input through the feedback amplifier and the feedback resistor.
6. The wideband active Balun low-noise amplifier topology according to claim 1 , wherein the first load is a passive narrow-band filter circuit or a frequency-dependent load circuit.
7. The wideband active Balun low-noise amplifier topology according to claim 1 , wherein the output noise generated by the first transconductance stage is transferred to the output by two paths; one is from the output of the first transconductance, passing through the third transconductance to the output, the other is from the output of the first transconductance, passing through the feedback network and the second transconductance successively to the output; the phase shift of these two paths is just opposite from each other.