DREXEL UNIVERSITY

CAD LAB EXPERIMENT III Objective: To compare performance of various semiconductor transistor based switch topologies

Olaniyi Q. Jinadu 2/20/2015

CAD Experiment III: Switches Objective: To compare performance of various semiconductor transistor based switch topologies A. Simulations Set-up A: 1. Use “on” and “off” model of a transistor switch, where the equivalent

circuit model for “on” position is a shunt RC (C=0. 1 pF and R= 2.5 ) in series with resistor of 1 . T

position is a shunt RC (C=0.35 pF and R= 10 k )

1.5 . 2. Compare switch performance for series and shunt configurations in terms of

isolation and insertion loss. Simulate and plot SPST switch insertion loss and isolation as a function of frequency from 100 MHz to 3 GHz.

3. Simulate and plot switch insertion loss and isolation of SPST switch as a function of frequency from 100 MHz to 3 GHz. Compare switch performance for a T network (series, shunt, series) and PI network (shunt, series, shunt) configurations in terms in terms of isolation and insertion loss against a commercial series and shunt (e.g., MASWSS0161).

4. Design a single pole double through (SPDT) switch using a series and shunt switch. Simulate and plot switch insertion loss and isolation as a function of frequency from 100 MHz to 3 GHz.

5. If this SPDT switch is packaged in a SOIC-8 package (i.e., MASWSS0161) show the layout for RF operation at 900 MHz with a 10% bandwidth and control signals of 500kHz.

6. Prepare a layout of this switch realization on FR4 substrate including control circuits.

B. Simulations Set-up B: 1. Consider a compensation network by adding a compensating shunt inductor.

Calculate the value of this inductor for optimum performance at 900 MHz. 2. Simulate and plot switch insertion loss and isolation as a function of

frequency from 100 MHz to 3 GHz for a T network (series, shunt, series). Compare the results of compensated with the uncompensated one.

Questions and HW Problems: 1) Discuss design and layout of the control circuits for switching operation at

1MHz rate versus a QPSK data rate of 64 Mb/s. Do you realize the compensating inductor in distributed or lumped for 500MHz compared to 8GHz?

2) What is the impact of self-resonant frequency and Q factor of the compensating inductor on switch performance? How about switch performance, if you use a distributed element using Richard’s transform?

3) How would you design and implement bandpass SPDT switches using the “on” and “off” circuit model of transistor switch? Simulate its performance.

SIMULATIONS SET-UP A:

ON SWITCH OFF SWITCH

Using the on and off switch configuration, the IL of both switches were observed from 100MHz to 3 GHz using the below configurations;

The result of this simulation is seen below;

ANALYSIS: As the results above show, the insertion loss for the on switch shows that the switch allows almost 100% of the power sent and there is an isolation loss for the off switch that tends towards 1.

SERIES AND SHUNT CONFIGURATION – ON SWITCH:

ON SWITCH CONFIGURATION

INSERTION LOSS S21

ANALYSIS: When the ON switch is in the series configuration it acts as an ON switch allowing almost all of the power to flow through but when the ON switch is in the shunt configuration it does not allow power flow through it.

SERIES AND SHUNT CONFIGURATION – OFF SWITCH:

OFF SWITCH CONFIGURATION

ISOLATION LOSS S21

ANALYSIS: When the OFF switch is in the series configuration it acts as an OFF switch allowing an isolation loss that tends to 1 but when the OFF switch is in the shunt configuration starts out with an isolation loss of 1 which reduces over time.

TEE AND PI CONFIGURATION – ON SWITCH:

ON SWITCH CONFIGURATION

INSERTION LOSS S21

Insertion loss of the MACOM MASWSS0161:

TEE AND PI CONFIGURATION – OFF SWITCH:

OFF SWITCH CONFIGURATION

INSERTION LOSS S21

Insertion loss of the MACOM MASWSS0161:

SINGLE POLE DOUBLE THROW (SPDT) SWITCH:

SINGLE POLE DOUBLE THROW (SPDT) SWITCH CONFIGURATION

INSERTION LOSS S21

ANALYSIS: The SPDT switch provides a more stable insertion loss and isolation loss to both the ON and OFF switch of the SPDT respectively. And the switch also gives the option of versatility and duality when needed i.e. you can use one switch for both functions depending on what you need the switch to do. Layout of SPDT switch packaged in a SOIC-8 package (i.e., MASWSS0161) for RF operation at 900 MHz with a 10% bandwidth and control signals of 500 kHz.

SIMULATION SET-UP B: COMPENSATED TEE & PI SWITCHED VERSUS UNCOMPENSATED SWITCHES

COMPENSATED ON SWITCH COMPENSATED OFF SWITCH

𝐿 =1

𝜔2𝐶=

1(2𝜋 × 900𝑀𝐻𝑧)2 × 0.1𝑝𝐹

= 312.7𝑛𝐻

𝐿 =1

𝜔2𝐶=

1(2𝜋 × 900𝑀𝐻𝑧)2 × 0.35𝑝𝐹

= 89.35 𝑛𝐻

ON-SWITCH TEE CONFIGURATION

INSERTION LOSS S21

OFF-SWITCH TEE CONFIGURATION

INSERTION LOSS S21

ON-SWITCH PI CONFIGURATION

INSERTION LOSS S21

OFF-SWITCH PI CONFIGURATION

INSERTION LOSS S21

ANALYSIS: The compensation inductor is used to account for the parasitic nature of the lumped elements. As we can see from the above results, at the design frequency of 900 MHZ, the compensated switches perform better than the uncompensated switched by accounting for the parasitic effects of the lumped elements by either allowing maximum amount of power to flow through (ON switch) or by not allowing any power to flow through (OFF switch). CONCLUSION: The insertion loss for the on switch shows that the switch allows almost 100% of the power sent and there is an isolation loss for the off switch that tends towards 1. When the OFF switch is in the series configuration it acts as an OFF switch allowing an isolation loss that tends to 1 but when the OFF switch is in the shunt configuration starts out with an isolation loss of 1 which reduces over time. The SPDT switch provides a more stable insertion loss and isolation loss to both the ON and OFF switch of the SPDT respectively. And the switch also gives the option of versatility and duality when needed i.e. you can use one switch for both functions depending on what you need the switch to do. The compensated switches perform better than the uncompensated switched by accounting for the parasitic effects of the lumped elements by either allowing maximum amount of power to flow through (ON switch) or by not allowing any power to flow through (OFF switch).

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