Signal Chain Errors
Local Errors vs. RTI
How do the errors from a circuit bock contribute to the local Analysis Node and also Referred to Input (RTI) of the 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
CIRCUIT 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 Offset Error?
Let's calculate the error both at the Analysis Node and Referred to Input (RTI) of the Signal Chain.
- Select Error Source
e = voff - Choose Analysis Node:
vo2 - Calc Offset Sensitivity:
S = vo2 / voff = R2/R1+1 - Calc Error at Analysis Node
∆Voffset = e * S = voff * (R2/R1+1) - Calc Gain from Signal Chain Input to Analysis Node
Ka = vo2 / vs = K1*K2 - Calc Error Referred to Input (RTI):
∆Voffset_rti = ∆Voffset / Ka
GAIN ERROR - BLOCK 2
How does R1's Tolerance impact the Gain Error?
Let's calculate the gain errors both at the Analysis Node and Referred to Input (RTI) of the Signal Chain.
- Select Error Source
e = R1_Tol - Choose Analysis Node
vo2 - Calc Gain Sensitivity
K2 = vo2/vo1 = -R2/R1
S = (∆K2/K2) / (∆R1/R1) = -1.0 - Calc Gain Error at Analysis Node
Voffset = e * S = Tol_R1 * -1.0 - Gain Error Referred to Input (RTI):
NOTE - Normalized gain same at input!
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