Chapter 3 Down-Conversion Mixer Circuit Design
3.7 Total circuit
Finally we can have the complete circuit.
Fig 3.17 Total circuit
In Fig 3.16, all the DC_feeds or DC_blocks we can use RF bias tee to achieve their functions.
Fig 3.18 Circuit Layout
For measure convenient, we plot some pads that we can bound wires them.
Using this pad we can measure some DC data, without use any RF probe or any RF instrument.
Table 3.1 Voltage and Current
VDD VRF VLo Icircuit Power Itotal
1.8V 0.7V 1V 0.98mA 1.7mW 27.3mA
Fig 3.19 Implementation
31
Chapter 4
Simulation and Measurement Result 4.1 Simulation
We simulated both with and without the cross capacitance data. But with
capacitance, we simulated post-layout circuit. Without capacitance simulated pre-layout data.
m1freq=
conversion_gain=5.89610.00MHz
10.0000000 10.0000000 10.0000000 10.0000000 10.0000000 10.0000000 10.0000000
10.0000000 10.0000000
5.8958152
10.0000000 10.0000000 10.0000000 10.0000000 10.0000000 10.0000000 10.0000000
10.0000000 10.0000000
32
33
-25 -20 -15 -10 -5 0 5
35
Table 4.1 Compare with C and without C
4.2 Measurement
In this section, we show two conditions of voltage. First is the origin voltage’s
situation. The other is we tune a little VDD voltage to make the results close to our simulation data.
Gain = ( measure_data – RF_port_loss ) – ( RF_input + IF_loss )
Isolation_Lo-IF = ( measure_data – IF_port_loss ) – ( Lo_input + Lo_loss ) Isolation_Lo-RF = ( measure_data – RF_port_loss ) – ( Lo_input + Lo_loss )
(a) Condition 1
(b) Condition 2 Fig 4.6 Gain
(a) Condition1
(a) Condition1
(b) Condition 2 Fig 4.8 Isolation Lo-IF
-30 -20 -10 0 10
4.3 Specification
simulation data, but condition 2’s other data are more likely simulation. So finally we choose condition 2’s data as our final data.Chapter 5 Design Flow 5.1 Design flow
The simulation software ADS designer is used to design the circuit. ADS momentum is used to do EM simulation. After the layout of circuit is finished, DRC
& LVS & LPE is done to check the correction for the design.
Chapter 6
Conclusion and Improvement 6.1 Conclusion
Although low power and good characteristics cannot take both, but we still can improve them to be better. We design a single-balance structure mixer, with 2.72mW of power consumption, 6.04dB of gain, -8.45dB of Lo-IF isolation, -61.88dB of Lo-RF isolation, 2dBm of IIP3, and 17.76dB of noise figure. In our measurement and simulation, noise figure is measure or simulate by single side band. So we need to minus 3dB as double side band measure. Now we compare our design to other reference.
As we can see on table 6.1, the power of our design is the best in the table, and also twice less than others. That’s because the other reference always using
double-balance structure to implement their idea circuit. Our performance in this table is almost the best design, but not in Lo-IF isolation. Born defect of single-balance structure is really cannot be totally cured. But we still improve a lot from origin 0dB to -8.45dB.
Table 6.1 Comparison of Mixer performance
*2SSB measurement, minus 3dB as DSB data.
6.2 Improvement
The most important thing we need to improvement is Lo-IF isolation. After the project, we can find out two ways to improve it.
The first way is that we can change the layout. In fig 3.17, we can see lots of DC pad for bound wires. So many metal overlapping and close to each others may cause huge capacitance. Lo signal is 5.81GHz frequency, so the capacitance effect would more seriously. So if we cancel the pads and bias the voltages by bias tee, it can make the effect weaker.
As we mention before, Lo signal in IF port has two phases, and our design can only cancel one of it. But using Lo input is not the only way to cancel the signal, we can also find that in IF+ and IF- port, they have complete opposite phases of Lo feed-through. So we can use this situation and try another way to cancel them by each others.
Although our power is lower than others, but there still has chance to improve it.
If we add body bias to change Vth of MOS, the current can be achieved by smaller VDD. By this way, we can make the DC power lower.
Reference
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