Signal Chain Errors

What are Local Block vs. RTI Errors?

 

How do all the errors from each circuit block contribute to the overall spec of a Signal Chain?

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SIGNAL CHAIN - MULTI BLOCKS

Let's explore a signal chain with three circuit blocks.

where

• vs - source voltage (sensor, device, etc.) to be measured.
• vo1,2,3 - output voltage of each block
• K1,2,3 - signal gain of each block

 

BLOCK 2

What's inside of Block 2?

• U1 - inverting amplifier.
• K2 = vo2 / vo1 = -R2/R1

 

OFFSET ERROR - BLOCK 2

How does voff impact the local block and the overall OFFSET specification?

Let's calculate the errors both at the Local Block and Referred to Input (RTI) at vs.

• Choose Analysis Node:
     vo2
• Offset Sensitivity: 
     S = vo2 / voff = R2/R1+1
• Error at Analysis Node: 
     Voffset = e * S = voff * (R2/R1+1)
• Gain from Input Source to Analysis Node
     Ka = vo2 / vs = K1*K2
• Error Referred to Input (RTI):
     Voffset_rti = Voffset / Ka

 

GAIN ERROR - BLOCK 2

How does R1's Tolerance impact the local block and the overall GAIN specification?

Let's calculate the gain errors both at the Local Block and Referred to Input (RTI) at vs.

• Choose Analysis Node
     vo2
• Local Block Gain
     K2 = vo2/vo1 = -R2/R1
• Gain Sensitivity: 
     S = (dK2/K2) / (dR1/R1) = -1.0
• Gain Error at Local Block: 
     Voffset = e * S = Tol_R1 * -1.0
• Gain Error Referred to Input (RTI):
     NOTE! Same as Local for Gain Errors.
     (Why? See RTI and RTO Errors).

 

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