M2j - Low Noise Amplifier


The M2j module is a low noise amplifier initially designed for use in reflectometry. It has been optimised for use with the F1d IQ Demodulator with a 40 MHz to 1.5 GHz frequency range. This is reflected in the gain flatness of M2j: within 3dB from 40 MHz to 1.4 GHz.

Below is a block diagram of the inner workings of the module. The first stages are two Low Noise Amplifiers (LNA). Following these is a variable attenuator (controlled by a DAC or a potentiometer) to allow for a 30+ dB output power tuning range. The output stage contains multiple 20dB power amplifiers to be able to reach a 20 dBm maximum output power. A level detector is placed near the output to notify the user that the amplifier is reaching its 1dB compression point.

M2j block diagram

The figure below shows the S21 at both minimum and maximum gain. Both curves within 3dB from 40 MHz to 1.5 GHz. Over the whole frequency span, the tuning range remains 35 dB.


Parameter Value Units Conditions
Gain 35 to 70 dB Within 3dB from: 40 MHz ≤ f ≤ 1200 MHz
Noise Figure 1.3 dB At 70 dB gain
5.7 dB At 35 dB gain
P1dB 20 dBm 1 dB Compression point
S11 < 10 dB For 40 MHz ≤ f ≤ 2200 MHz
Spectral Purity
LED Clip Level 18 dBm

Cascaded Noise Figure

The noise figure of the M2j increases with a decreasing gain setting as seen in the specifications. Let’s look at the effect of this increased noise on the total setup. In the figure below we see a simplified setup consisting of a cryogenic amplifier, a coaxial cable running from 4K to room temperature and the M2j amplifier. The cryoamp numbers are based on the Caltech CITLF3 amplifier. From the figure we can see that the increase in noise of the M2j is negligible for the total system noise. It also shows the need for a cryogenic amplifier with high gain and a low noise figure: it determines the noise figure of the system.

M2j Noise Figure System Cascade