Low Noise Amplifier and Input/Output Phase

Electrical Engineering Asked by Jay on November 4, 2020

I’ve been designing LNAs for a brief time and I was wondering why the input and output phases is usually never cared for or measured when measuring the specs of the LNA. For example, the only specs we cared about when designing the LNA were gain, intermodulation point (3rd), and power.

I guess this question would also apply to general use of amplifiers such as Op-Amps (with feedback) but why is phase for different frequencies not cared about (except for 180 deg frequency point for checking stability) or is never measured? I would assume that if a signal consisted of a bandwidth from freq ‘a’ to freq ‘b’, you would need the entire bandwidth of frequencies, from input to output, to all have the same phase (i.e., not a single or more frequencies are delayed/ahead) in order to demodulate the entire bandwidth of signal.

2 Answers

LNA phase is cared for in at least one case. Phase matching is critical to successfully combine multiple receive antennas to form an array. Transmission lines must be equal length, combiners phase matched and it is desirable to have LNAs at each antenna to reduce transmission line and combiner losses.

Answered by Tom1975 on November 4, 2020

One does not usually place an LNA inside an RF feedback loop, so as long as the group delay across the frequency range of interest is reasonably constant (It generally is) it is just not that important. Also LNAs cannot in general be assumed to be small compared to the operating wavelength, if I need to tune phase at 24GHz I do it with a short length of transmission line...

Opamps are basically always used inside a feedback loop which makes phase shift in the naked opamp basically only a concern for stability but not one that impacts the overall phase shift of the circuit because the feedback loop defines the phase shift as long as there is sufficient open loop gain (Opamp circuits are pretty much all electrically small).

Answered by Dan Mills on November 4, 2020

Add your own answers!

Related Questions

Cannot find this 6 pin IC 362J38

1  Asked on January 2, 2021 by richl


Small shock from mains

3  Asked on January 1, 2021 by mr_random_guy


MCP3461 analog side broken “somehow”?

1  Asked on December 30, 2020 by spiros-makris


UVC Lamp causes Atmega 328P to malfunction

1  Asked on December 29, 2020 by shafiyyah


Voltage doubler for LED backlight

2  Asked on December 29, 2020 by mike-spivey


I/O panel filtering for shielded room

1  Asked on December 29, 2020 by lars-petersson


Mute / blank an amplifier fast

0  Asked on December 28, 2020 by p-egli


MOSFET Driver P-channel

0  Asked on December 28, 2020 by brent-thierens


How to calculate torque of the motor?

1  Asked on December 27, 2020 by tushar-dubey


Regarding Ferrite Bead

3  Asked on December 27, 2020


Ask a Question

Get help from others!

© 2022 All rights reserved. Sites we Love: PCI Database, MenuIva, UKBizDB, Menu Kuliner, Sharing RPP