Double-balanced Mixer Design(MOS Gilbert Cell Mixer )

NI Multisim 10

Mixer design parameter

Conversion GainNoise FigureIsolationLinearity-

1dB Compression point: Intermodulation (IM3) performance (The IM3 performance is often summarised by giving the 3rd Order

Intercept point (IM3 Intercept)

Basic circuit of the Gilbert Cell Doublebalanced mixer (DBM)

Design steps:

(1) Select a value for Rs. If we start with the LNA design , Rs will be realized by an inductor Ls.

(2) Using the design equations decide on the IM3 value required to calculate the voltage overdrive (Vgs-VT).

(3) Calculate gm and check for compliance of mixer gain with a suitable load resistance.

(4) Determine LO (local oscillator) switching W by selecting minimum L allowed and assuming that the overdrive voltage (Vgs-VT) will be between 0.2 and 0.4V.

Design Criteria

Parameter Specification Units

Frequency 2.45 to 2.85 GHz

Noise Figure (DSB) < 10 dBm

IIM3 Intercept Point (Input) >20 dBm

Voltage Gain >8 dB

Power consumption <100 mW

Source impedance 50 ohms

Load impedance 500 ohms

Voltage Supply ± 2.5 V

Design Step 1:

Using the spice model data for the Agilent CMOS14 0.5um

we have:L = 0.6umµ0 = 433 cm^2/(V*s)Ө= 0.5Rs = 10 ohmsVT = 0.67VVsat = 1.73E5 m/s

Design Step 2:

Useful design equations are:

Let’s make a table using these equations. Using Vod from 0.01 to 5V we find the table below:

Design Step 2:

From table we can see that to achieve a minimumIM3 value of 20dBm we require a VOT of 1V. As Vt forthis process is 0.67V, the value of Vgs will be (1-0.67) =0.33V.

Steps 3+4:

gain converion to dB Convert

Now with gm calculated we can W (Assuming we takethe minimum gate length to be 0.6um and assume a current of 3mA) ie.

We can now run our first simulation by assuming alldevices have W = 233um and L = 0.6um, tail current of 6mA, source resistors of 10 ohms and load resistors of 500 ohms.

Design your own component

Choose Tools/Component Wizard. Step 1:select simulation only Step 2: No of pins 3

Design your own component

Step 3: Enter symbol information GO “Copy from DB” Chose your component

Step 4:

Go on………

Design your own component

Step 5: Model name: RF_MOS_TESTGo select from DBChose RF> P123 componentGo Model data report

Design your own component

Modify the value as we get from calculation, like

W=0.000233L=0.6uKp=171E-6

and so on

Design your own component

Step 7: Add familySelect

group as

RF….

Design your own component

From select your component (Ctrl+W) from ‘User Database’

Built the mixer ckt shown before.

Build your circuit

U1

RF_MOS_Test

U2

RF_MOS_Test

U3

RF_MOS_Test

U4

RF_MOS_Test

U5

RF_MOS_Test

U6

RF_MOS_Test

U7

RF_MOS_Test

R1500Ω R2

500Ω

74

VCC5V

0

8

6

V2

1 Vpk 1kHz 0°

3

V1BIPOLAR_VOLTAGE

9

10

2

VCC

5

Probe4,Probe4

V: V(p-p): V(rms): V(dc): I: I(p-p): I(rms): I(dc): Freq.:

Probe5,Probe3

V: V(p-p): V(rms): V(dc): I: I(p-p): I(rms): I(dc): Freq.:

Probe2,Probe2

V: V(p-p): V(rms): V(dc): I: I(p-p): I(rms): I(dc): Freq.:

Probe1,Probe1

V: V(p-p): V(rms): V(dc): I: I(p-p): I(rms): I(dc): Freq.:

Simulation Results-Noise analysis

Select Simulate/Analyses/Noise Analysis. Select the Analysis Parameters tab and set the following:

Input noise reference source—vv2 Output node—V(probe1) Reference node—V(0)

Select the Frequency Parameters tab, and set the following: FSTART—1Hz FSTOP—10GHz Sweep type—Decade Number of points per decade—5 Vertical Scale—Logarithmic

Simulation Results-Noise analysis

Select the Output tab, select the following variables for plot during simulation: onoise_rr1 & onoise_rr2

Click Simulate. A chart displays in the Grapher with data similar to the expected results.

This graph shows that the noise voltage is constant for lower frequencies. For higher frequencies the noise voltage drops considerably.

Simulation Results-Noise Figure Analysis

Notice that the maximum gain appears at approximately 1GHz.

Simulation Results-Noise Figure Analysis

To set up Noise Figure Analysis using the circuit shown, follow the steps listed below.

Select Simulate/Analyses/Noise Figure Analysis. Under the Analysis Parameters tab, set the following:

Input noise reference source to vv2 (which is the input AC Source).

Output node must be V(probe1) Reference node will default to V0 Frequency must be set to 1e+009 Temperature must be set to 27 degrees C.

Click Simulate. The following displays.

Simulation Results-Noise Figure Analysis

Therefore, the Noise Figure for the circuit is approximately –17 dB