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Gilbert Cell Mixer Example with Layout
This is a downconverting Gilbert Cell mixer designed using the Generic_GenBic35 Design kit from AWR.
The Gilbert Cell mixer is simulated with a range of LO input power levels. The measurements made include the mixer's conversion loss, output power spectrum and voltage waveforms, RF-LO and LO-RF isolations, IP3, Noise Figure, and Noise Spectral Density . Separate test bench is setup for each set of measurements. After the simulations are completed, activate the tuner (Simulate > Tune) to sort through the data and see the output power spectrum and voltage waveforms at varying LO power levels.
Annotations have also been added to the Bias Circuit which is off the chip.
The example has IP3 measurement disabled to keep the simulation time short. Since IP3 simulation of a mixer envolves three tones , the similation is significantly longer.
To minimize the mismatch between the differential pair due to gradient effect, the mixing transistors are are split into two and laid out using the common centroid technique where as switching stage transistors are laid out using the interdigitating technique.
Test Benches and Simulation
It is a best practice to create a separate test bench for each set of measurements. This makes the measurements setup very easy and simple and gives user the more control over the types of simulation. There are 3 test benches in this project.
This test benches is used for most of the nonlinear measurements. Tone 1 applied to PORT 1 defines the RF frequency of 2.1 GHz. The RF frequency is defined as the Document Frequency (right click Mixer_Test_Bench > Options). Tone 2 applied to PORT 2 defines the LO frequency of 1.95 GHz and swept power.
This test bench is setup for IP3 measurement. RF tones separated by 0.01 GHz are applied at PORT 1.
This test bench is setup for Noise Simulation. A NLNOISE block which controls the nonlinear noise simulator needs to be placed in the schematic for all nonlinear noise simulations.
Conversion Gain and Input Return Loss Graph
This graph shows the mixer conversion loss versus LO power. The conversion loss is calculated using the large signal s-parameter measurement, LSSnm, with the output signal at PORT_3 (IF)
IF Power vs LO Power Graph
This graph shows the IF output power versus LO power.
IF Spectrum Graph
This graph shows the IF output spectrum for a single LO power. As mentioned above, use the tuner (Simulate > Tune) to view the IF output spectrum at the different simulated LO power levels.
IF Voltage Waveforms Graph
This graph shows the IF output voltage waveforms for a single LO power. As mentioned above, use the tuner (Simulate > Tune) to view the IF Output voltage waveforms at the different simulated LO power levels.
This graph shows the RF to LO and LO to RF isolation.