4.9.5 Sigma-Delta Filter Module (SDFM)
The SDFM is a four-channel digital filter designed specifically for current measurement and resolver position decoding in motor control applications. Each channel can receive an independent sigma-delta (ΣΔ) modulated bit stream. The bit streams are processed by four individually programmable digital decimation filters. The filter set includes a fast comparator for immediate digital threshold comparisons for overcurrent and undercurrent monitoring. Figure 4-54 shows a block diagram of the SDFMs.
SDFM features include:
- Eight external pins per SDFM module:
- Four sigma-delta data input pins per SDFM module (SDx_Dy, where x = 1 to 2 and y = 1 to 4)
- Four sigma-delta clock input pins per SDFM module (SDx_Cy, where x = 1 to 2 and y = 1 to 4)
- Four different configurable modulator clock modes:
- Modulator clock rate equals modulator data rate
- Modulator clock rate running at half the modulator data rate
- Modulator data is Manchester encoded. Modulator clock not required.
- Modulator clock rate is double that of modulator data rate
- Four independent configurable comparator units:
- Four different filter type selection (Sinc1/Sinc2/Sincfast/Sinc3) options available
- Ability to detect over-value and under-value conditions
- Comparator Over-Sampling Ratio (COSR) value for comparator programmable from 1 to 32
- Four independent configurable data filter units:
- Four different filter type selection (Sinc1/Sinc2/Sincfast/Sinc3) options available
- Data filter Over-Sampling Ratio (DOSR) value for data filter unit programmable from 1 to 256
- Ability to enable or disable individual filter module
- Ability to synchronize all four independent filters of a SDFM module using the Master Filter Enable (MFE) bit or the PWM signals.
- Filter data can be 16-bit or 32-bit representation
- PWMs can be used to generate modulator clock for sigma-delta modulators