SPRUJ55D September 2023 – July 2025 AM263P2 , AM263P2-Q1 , AM263P4 , AM263P4-Q1
The resolver excitation signal gets modulated by the rotation of the motor creating sine and cosine envelopes(sine and cosine modulated Excitation signal). The demodulation happens by sampling the incoming sine and cosine signals at the peaks(as shown in Figure 7-153) of the excitation signal. Since there will be a phase delay along the signal chain, in a real system the peaks can be at any point. So to sample at the peaks, the RDC oversamples the excitation signal and runs an auto-detection loop to decide the ideal sampling time.
The registers associated with Auto Sample Time select are REGS_SAMPLE_CFG1_x, REGS_SAMPLE_CFG2_x and REGS_DEC_GF_CFGx.
The RDC block has an auto-detect feature to compensate for the delay in signal chain and find the ideal sample point. Before the software enables IDEAL_SAMPLE_TIME(register REGS_SAMPLE_CFG1_x[23:16]) selection logic, it needs to make sure the excitation frequency from the external amplifier has settled. The threshold value SAMPLE_DET_THRESHOLD(register REGS_SAMPLE_CFG2_x[31:16]) is used to ignore unsettled, low amplitude data from external amplifier before peak detection starts.
Figure 7-153 Oversampling the Excitation Signal and Deciding Ideal Sampling TimeAuto ideal sample detection is performed through positive peak detection of modulation signal peaks on either Sin or Cos channel. Note that depending where the motor and hence Resolver shaft position is, the ideal sample peaks may be negative or positive.
For example, consider the Sin channel being used for peak detection. With respect to the Figure 7-154, if the rotor zero position is in Q1 or Q2 region, note that the positive peaks of the excitation signal will give the correct sampling point. However if the peak detection is run when the zero position of the rotor is in Q3 or Q4 region, then the positive peak detection of excitation signal will cause the angle position to be shifted by 180 degrees which has to be accounted for accordingly. Hence the RDC sub-system's algorithm has different modes, for finding the ideal sampling position as described below in Section 7.5.3.2.2.1.4.1 to Section 7.5.3.2.2.1.4.4 sections.
Figure 7-155 Excitation Signal vs Internal Counters. If ENABLE_BOTTOM(register REGS_DEC_GF_CFGx[24]) control bit is set, then sin and cos signals are sampled at both positive and negative peaks of the excitation signal. RDC auto-corrects the sign of the sample. This improves the response time of the loop, since without increasing the sampling rate, data rate of angle output is doubled.
Figure 7-156 Sine Modulated Excitation Frequency.
Figure 7-157 Ideal Sampling Points. The above two figures show a sine signal(sine modulated excitation frequency signal) and Ideal sample points shown on the sine signal.