SLASEC8B February 2017 – January 2019 PGA460-Q1
The PGA460-Q1 threshold assignments are organized in two presets: Preset1 and Preset2. Both of these presets have an independent memory map for threshold segment allocation. The PGA460-Q1 device supports up to 12 threshold segments for each preset defined by the threshold segment points (TSP) in the P1_THR_[0:15] registers for Preset1 and P2_THR_[0:15]registers for Preset2.
Figure 8 shows an example of a threshold assignment.
As shown in Figure 8, each TSP is described in the (time, level) format while Px is the preset number (P1 for Preset1, P2 for Preset2). Additionally, only the initial segment time parameter (TH_Px_T1) value is expressed in terms of absolute time, while all following TSP times (TH_Px_Tx parameters) are expressed as a delta time between the absolute time value of the previous TSP and the absolute time value of the current TSP. The level values of each TSP (TH_Px_Lx parameters) are all expressed in an absolute LSB-level value and are unrelated from each other. The TSP level threshold value at any given time moment is determined by the PGA460-Q1 device as a linear interpolation function between the two neighboring threshold segment points
As shown in Figure 8, the initial segment has a constant threshold value determined by the TH_Px_L1 parameter until reaching the start of the first segment and also the 12th segment will have a constant threshold value determined by the TH_Px_L12 parameter until reaching the end of record time defined by the Px_REC parameter.
The TH_Px_L1 through TH_Px_L8 threshold parameters are 5-bits wide and the TH_Px_L9 through TH_Px_L12 parameters are 8-bits wide. These sizes help save memory space and at the same time allow higher resolution for long-range detection of weak echo signals in presence of noise while keeping the range constant across all TSPs. Because the TH_Px_L1 through TH_Px_L8 resolution is an 8 LSB, a threshold offset is defined to allow finer adjustment of the threshold map for short-range detection.