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Sinusoidal encoder signal tuning with Power PMAC


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If the sinusoidal encoder signals have some problems in term of the DC offset, phase offset, and amplitude. Is it possible to tune the signal through the axis interface board ACC-24E3 in the Power PMAC system?


I have not been able to find this information in the Hardware Reference. It will be useful to have some hint. THANKS!

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According to the manual:

Gate3.Chan[j].AdcOffset[k] elements specify the bias-correction values that are automatically added to the 32-bit registers for the primary “encoder” ADC data values for the channel before the IC performs subsequent arctangent and sum-of-squares calculations.



(1) As a result, this AdcOffset is NOT used to make any correction in the zero-crossing detection of sin/cos signal, right?


(2) What is the differerence between this register and

EncTable[n].CosBias/EncTable[n].SinBias ?

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(1) You are correct that these AdcOffset values are not used to make any corrections in the zero-crossing detection of the incoming sine and cosine signals, so these do not help in the hardware capture and compare circuits in the ASIC, which are based on the zero crossings.


(2) These hardware offset registers in the ASIC for the ACC-24E3 interpolator perform the same function that the encoder table SinBias and CosBias software offset values perform for the older ACC-51E interpolator, where the arctangent is calculated by the processor.


These hardware and software offset values can be used to compensate for DC offset in the signals, but not phase offset or magnitude mismatch.


In the new V1.5 firmware being released this month, the encoder table entry for arctangent extension of sine/cosine encoders has several added features:


a) A new correction element EncTable[n].TanHalfPhi for phase error correction (Phi is the error angle from the ideal 90 degrees).


b) A new correction element EncTable[n].CoverSerror (cosine over sine error) to compensate for magnitude mismatch


c) A new control element EncTable[n].index5 to permit this software extension to be used with the newer ASIC. Note that this bypasses the hardware extension done in the Gate3 IC, and replicates it in software, but with these additional correction terms. Note that these corrections are used at the servo update rate, so will improve the quality of servo feedback, but will not help with hardware capture and compare features.

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(1) What is the convertion factor from the value of to the voltage value?

- The manual indicate is a 24-bit ADC

- However, our measurment show value of ~1.5e9 (peak-to-peak).

- Is for the differential signal of +/-sin or +/-cos?


(2) What is the converation factor from voltage value to the value of ?

- The manual indicates AdcOffset is 32-bit value

- Is it for the voltage range of 1?

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The manual is in error on the scaling of the AdcEnc registers. The processor reads them as full 32-bit registers (even though there will never be more than 24 bits of data, so the lowest bits are not "real"). So these registers have a numerical range of +/=2^31. To these values, the user-settable 32-bit AdcOffset values are added before arctangent and sum of squares are computed.


The interpolator front end circuitry is scaled to provide full range into the ADCs (and therefore these numerical registers) when the input voltage is 1.2Vpp.

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