## Ideal Single Pole Double Throw Switch (Closed Form): SPDT

### Summary

The SPDT model allows you to implement an ideal single pole double throw switch whose position is determined by the STATE parameter. The BIT parameter allows you to control multiple switches using one STATE parameter by specifying the significant binary bit on which the switch operates.

### Parameters

Name Description Unit Type Default
ID Element ID Text S
STATE Switch state   0
BIT Defines On/Off bit of state   0

### Parameter Details

STATE. An integer greater than or equal to zero which is converted to a binary number. For example, if STATE is equal to 14 in base 10, it is converted into 001110 in binary, or base 2.

BIT. An integer greater than or equal to zero which determines the significant bit the switch operates on 2BIT. For example, if STATE is equal to 14 as given above, and BIT is equal to zero, then the switch is in the OFF state. However, if BIT is equal to 1, the switch is in the ON state.

1. STATE ≥ 0

2. 0 ≤BIT ≤ 30

### Implementation Details

4-Bit Truth Table

STATEBase 10 STATEBASE 2 BIT=3 BIT=2 BIT=1 BIT=0
0 0000 OFF OFF OFF OFF
1 0001 OFF OFF OFF ON
2 0010 OFF OFF ON OFF
3 0011 OFF OFF ON ON
4 0100 OFF ON OFF OFF
5 0101 OFF ON OFF ON
6 0110 OFF ON ON OFF
7 0111 OFF ON ON ON
8 1000 ON OFF OFF OFF
9 1001 ON OFF OFF ON
10 1010 ON OFF ON OFF
11 1011 ON OFF ON ON
12 1100 ON ON OFF OFF
13 1101 ON ON OFF ON
14 1110 ON ON ON OFF
15 1111 ON ON ON ON

### Layout

This element does not have an assigned layout cell. You can assign artwork cells to any element. See “Assigning Artwork Cells to Layout of Schematic Elements” for details.

### Recommendations for Use

You can use SPDT to create ideal digital components such as attenuators or phase shifters. See the phase shifter examples for how these are implemented in this type of design.

Several examples demonstrate how to properly use this element. The simplest case is where you want to do a simple switch between two paths. The following example shows switching between two different capacitor values.

A swept variable is used to sweep the two possible states. Note that BIT is set to 0. Setting up the graph to use the swept value on the x-axis produces a graph similar to the following.

You can get more complex with the switches by using the BIT setting, for example, switching between four different capacitor values.

Note that the left-most switch has BIT set to 1 and the two right switches have BIT set to 0. Sweeping four different states easily produces the four possible paths through the switch.