To reduce the drift of the AMR sensor outputs across temperature, the TMAG6181-Q1 features an automatic gain control circuitry where the device changes the gain of the output drivers to keep the final output within an appropriate voltage range on SIN_P, SIN_N, COS_P and COS_N. The AGC block uses the square root of the sum of the squared amplitudes of the two channels to sense amplitude of output signals and set gain selection. This means that the AGC block sets the gain for sine and cosine channels such that the peak-to-peak amplitude of single-ended voltages (V_OUT) is within the range listed in Specifications. The AGC block changes the gain of both the sine and cosine channels simultaneously and does not affect the angle accuracy.

If the outputs are out of the intended operating range, the AGC block changes the gain of the sine and cosine channels by a step size of ±1% V_CC at an interval of t_{agc_update}, approximately one second, as defined in Specifications. Figure 6-12 shows the differential AMR outputs for a continuously rotating input field. The shaded area represents the 'No AGC Control' band that represents ±5% of V_CC and is centered at 60% of VCC. Notice that the AGC loop reduces the gain of the sine and cosine channels and updates the amplitude of the sine and cosine signals when drift outside of the shaded region at a step size of 1% V_CC. If the outputs remain within the shaded region, then no action is taken by the AGC control loop.

Figure 6-12 Timing Diagram Showing the Operation of Automatic Gain Control