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RF2 team 3

Mixer

this is the final design of the mixer:

 

with parameters:

R4 = R5resistance2k ohm
M0 = M1length90u m
 width5u m
M2 = M3 = M4 = M5length50n m
 width1.8u m
M7length50n m
 width1.32u m
L0 = L1inductance1n H
C8 = C9capacitance7f F
C4 = C5capacitance10n F

with output waveform:






























 

and for clarity, the spectrum of this signal:































 
 

A standard double-balanced mixer is created, with an LC tank at the switching branches to give high output swing with reduced interpolation products. The output waveform is the differential signal, which is capacitively coupled to the load.

 

High frequency divider (Divide by 16).

The design consists of 4 chained CML D-Latch based frequency dividers with an output buffer between each stage, their connection diagram is given as:

 

Each divide by two circuit consists of two D-Latches in a negative feedback loop:

 

The implemented design for one such divide by two circuit is as follows:

 

with the parameters

ParameterValueNote
L_Core50 nm 
W_Core800 nm 
L_Latch50 nm 
W_Latch800 nm 
L_Buffer50 nm 
W_Buffer1 um 
L_Tail200 nm 
W_Tail250 nm 
L_Bias200 nm 
W_Bias250 nm 
RD1.365 kOhm 
RBuffer2/3/4/5 kOhmDepending on the stage
Ct0/4.7/14/32.5 fTDepending on the stage
CB100 fF 
RB50 kOhm 
I_Tail210 uA

The resulting output waveform (compared to the input waveform) after four stages is:

 

and the output spectrum:

 

Oscillator

For the oscillator a cross coupled LC topology has been chosen.
Tuning of the frequency is done using variable capacitors and a control voltage (this voltage can range from 0 to 0.65 V and yields a tuning range of around 1.2 GHz).
To obtain a square wave from the sinusoidal output initially attempts were made to achieve this with a differential pair.
Additional attempts to obtain a square wave were done with inverters and inverter based amplifiers.
Since a better result was obtained using the differential pair, this method has been implemented in the design.


Below figure shows the transient analysis of the oscillator. It can be seen that the square wave has a slope that is lower than that of the sine wave. Therefore it is considered a possibility to just feed the sine wave to the mixer instead of the square wave to achieve quick switching action.

  

Below figure tabulates the component values.

 

 

Power Amplifier

Goal: Design a power amplifier with 45 nm technology at 60 GHz

Specs: Output power transmitted @ 10 dBm

            Differential output voltage swing @ 2 Vpp

            Impedance hence 50 ohms

            Giving, current needed in output stage @ 40 mA peak to peak

This design consists of two stages with differential implementation

  1. Driver stage : Purely provides voltage gain.

  2. Power stage: Focuses on providing the current gain (keeping voltage swing constant) and hence power gain.

 

Fig 1 is the schematic of discussed PA

Fig 1

 

Table 1

ParameterValueParameterValue
W (M0, M1)300 nmW (M5, M6)20 um
L0, L19.5 nHL2, L31 nH
VDD10.8 VVDD21.2 V
VIN (+/-)0.5 V (bias) +/- 0.3 Vp ACI11100 uA
I1325 mAR0 (o/p Impedance)50 ohms
C0, C11 pFR1, R2
10 Kohms

Fig 2

Fig 2 shows the transient analysis of the Driver stage with differential input voltage swing @ 1.2 Vpp (achieved from mixer) and output voltage swing @ 2 Vpp (as per specs)

 

Fig 3

Fig 3 shows the transient analysis of combined PA. It is now seen that in the left hand plot the driver stage output swing is greatly attenuated (no longer @ 2 Vpp). As a result the final output from the second stage (VOUT+ and VOUT-) are asymmetric and not as expected. This is due to mismatch between the two stages.

An interstage matching network is to be implemented further.

 

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