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# dual amplifier

Hello, for the amplifier HMC471MS8G, by combining dual amplifier circuit, can i have a double gain (20db *2=40db)? thank you

## Top Replies

• Hi,

I have moved your question regarding the HMC471MS8G to the RF and Microwave community. Someone here should be able to assist you.

Thanks,

Kris

• Hi krisf,

By combining two coherent signals of equal amplitude you would not get 2X the number of dB of gain from each amp. The highest you could expect to obtain (when combining two equal amplitude signals 180 degrees out of phase with each other) is an additional 6 dB (over the single signal). That assumes you are able to combine the two signals with no loss. That said, the data sheet shows an "Application Circuit for Balanced Operation" which uses transformers to couple a single-ended RF input signal to both amps and to then combine their individual RF outputs to a single-ended output signal. The data sheet plots show performance for the single amplifier configurations and for the balanced operation configuration.

Regards,

SMcBride.

• Thank you krisf!

If I connect  the output of first amplifier to the input of second amplifier, in this case, could I get 2X the number of dB of gain from this dual channel amplifier? thank you again

Regards

• Hi y@n, I apologize that I referred to you as krisf earlier!

You are correct. If you were to cascade the two amplifiers as you have described, and the signal into the second amp of the cascade were to remain "small signal", then the two amp cascade would provide you with 2X the gain (in dB) of a single amp. I mentioned "small signal" because you will realize the full 2X gain only if the RF Pin to the second amplifier remains below the level where its gain has become compressed. As a numerical example, consider the data sheet Electrical Specifications table's typical gain and P1dB at 0.5 GHz, attached, with some yellow highlights and red notes. For RF Pin = -22 dBm to the first amp, the second amp will see RF Pin = -22 dBm + 21 dB = -1 dBm. With RF Pin = -1 dBm to the second amp, you will NOT obtain an RF Pout = -1 dBm + 21 dB = +20 dBm because the gain of the second amp will be compressed by 1 dB (since its Output P1dB is +19 dBm). Thus with RF Pin = -22 dBm to the first amp you would obtain only +20 dB of gain from the second amp and your total cascaded gain would be +21 dB + 20 dB = +41 dB (NOT +42 dB). The conclusion is that the RF Pin to the two amp cascade at 0.5 GHz should be kept far below -22 dBm in order to obtain the full cascaded, non-compressed gain of +42 dB.

Be certain to review the data sheet's Pin Descriptions table to understand the need for DC blocking caps, RF chokes, etc.

Regards,

SMcBride