RF2 team 3
Mixer
this is the final design of the mixer:
with parameters:
R4 = R5 | resistance | 2k ohm | |
M0 = M1 | length | 90u m | |
width | 5u m | ||
M2 = M3 = M4 = M5 | length | 50n m | |
width | 1.8u m | ||
M7 | length | 50n m | |
width | 1.32u m | ||
L0 = L1 | inductance | 1n H | |
C8 = C9 | capacitance | 7f F | |
C4 = C5 | capacitance | 10n 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
Parameter | Value | Note | |
L_Core | 50 nm | ||
W_Core | 800 nm | ||
L_Latch | 50 nm | ||
W_Latch | 800 nm | ||
L_Buffer | 50 nm | ||
W_Buffer | 1 um | ||
L_Tail | 200 nm | ||
W_Tail | 250 nm | ||
L_Bias | 200 nm | ||
W_Bias | 250 nm | ||
RD | 1.365 kOhm | ||
RBuffer | 2/3/4/5 kOhm | Depending on the stage | |
Ct | 0/4.7/14/32.5 fT | Depending on the stage | |
CB | 100 fF | ||
RB | 50 kOhm | ||
I_Tail | 210 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
Parameter | Value | Parameter | Value |
W (M0, M1) | 300 nm | W (M5, M6) | 20 um |
L0, L1 | 9.5 nH | L2, L3 | 1 nH |
VDD1 | 0.8 V | VDD2 | 1.2 V |
VIN (+/-) | 0.5 V (bias) +/- 0.3 Vp AC | I11 | 100 uA |
I13 | 25 mA | R0 (o/p Impedance) | 50 ohms |
C0, C1 | 1 pF | R1, 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.