Tuning and Signal-to-Noise Ratio (SNR)
Tuning and SNR
- Set MagSense Tuning parameters: Set the tuning parameters outlined in the Getting Started with MagSense section in the Inductive Sensing Design application note. The most critical parameters are the Lx clock frequency and the number of sub-conversions, the number of conversions per data sample. Ensure that the Lx clock frequency is set to the resonant frequency of the LC tank (f0).
Inductive-Sensing Tuning Flow
2. Measure SNR: See Ensure SNR Is Greater Than or Equal to 5:1 in the Inductive Sensing Design application note. If the SNR measured is greater than or equal to 5:1, proceed to Step 5; otherwise, enable filters and measure the SNR again.
To compute the SNR, acquire a fixed number of samples, for example 2,000 raw count samples, as Figure 17 shows, and measure the peak-to-peak noise count. Place your target at the required proximity-sensing distance and measure the shift in raw counts. The signal will be equal to the raw count (after placing the target) minus the average raw count (before placing the target.)
3. (SNR< 5:1) Enable FW filters or increase the number of sub-conversions: See Table 3 in the Inductive Sensing Design application note.
Simple filters such as median, average, and infinite impulse response (IIR) filters may not be able to attenuate the higher noise amplitude in sensors, so you may need to use the advanced low-pass filter (ALP filter). The ALP filter is designed specifically for attenuating noise in the inductive sensor and providing a fast response time. See Advanced Low-Pass (ALP) Filter section in the Inductive Sensing Design application note.
4. Max sub-conversions/All filters used: If all filters are enabled and the number of sub-conversions is set to a maximum, defined by Equation , debug is required to determine the reasons for the design not meeting SNR >= 5:1. See Design Debug in the Inductive Sensing Design application note.
5. (SNR ≥ 5:1) System meets timing: If SNR ≥ 5:1, it is important to check the system meets timing requirements. You might need to reduce the number of sub-conversions or remove filters if the SNR and scan time are high.
6. Set the system thresholds: After the scan time and SNR meet requirements, it is important to set the firmware thresholds for optimum detection of the target.
For more details on tuning, please check the Inductive Sensing Design Guide.