# Sound Activity Monitor Circuit for Low Power Consumption of Always-On Microphone Applications
## 3 Simulation Verification and Results
In low power mode, if a command is entered in silent state, the user is intentionally trying to enter a voice command and therefore does not speak quietly. Therefore, it may not be a big problem that the noise of the low power mode is about 50% greater than the noise of the normal power mode. This is especially true because when a sound is detected, it immediately switches to normal power mode before a single syllable has passed and takes measurements at a lower noise level. However, further research is needed on how appropriate the noise level is in low power mode. Figure 16 shows the simulation results for the full chain from SF to LOGIC. As shown in the _SF_INPUT_ of Figure 15, a signal consisting of no wave for 0.5 s and a sine wave having an amplitude of 1 mV\({}_{\text{pk}}\) and a frequency of 1 kHz for 0.5 s was repeatedly supplied to the SF. As soon as the signal was input at 0.5 s, a rising edge was generated at the _CMP_edge_, which soon generated a rising edge of the _WIP_ signal. The input signal was cut off at 1 s, but it can be seen that the _WIP_ signal continues to maintain at _HIGH_ even after 1 s. After the _SF_INPUT_ signal was cut off at 1 s, a rising edge occurred in the _enough_calm_ signal after 2 cycles of _CLK_, and the low active reset signal in the _WIP_ falling_ signal caused a falling edge in the _WIP_ signal. Since the _CMP_edge_ is still in _HIGH_, the input reaction of the LOGIC block \"A. WUP_RISING_GEN\" is in the deactivated state. Afterwards, it can be seen that the low active reset signal of the _EN_INPUT_ signal is generated at the first falling edge of the _TRG_Tfb_ signal generated by synthesizing _enough_calm_ and _CLK_. The low active reset signal value of the _EN_INPUT_ signal causes the _CMP_edge_ signal to become _LOW_, and the block A of the LOGIC can react to the input again. Accordingly, it can be seen that the _WIP_ signal becomes _HIGH_ again as the sine wave is input to the _SF_INPUT_ at 1.5 s.  
Figure 16: Full channel simulation results from SF to LOGIC. The designed circuit operates at 1.8 V, and the SF block consumes a current of 200 nA in low power mode and a current of 14.3 uA in normal power mode. The details of the DC current consumption of the SAM block are shown in Figure 17. The OA, AMP2, CMP, and LOGIC blocks consume 360 nA, 440 nA, 100 nA, and 4.8 nA, respectively, and the SAM consumes a total of 1 uA of DC current. The clock generator (CLK_GEN) drew an average of 2.1 nA of current. The reduction in power consumption due to the SAM feature may vary according to the user scenario. The average current consumption is 14.3 uA when only the SF block without the SAM block is operated in 24-h normal power mode. When using the SAM function, in normal power mode, SF consumes 14.3 uA and SAM consumes 1 uA, so the total current is 15.3 uA. In low power mode, SF consumes 0.2 uA and SAM consumes 1 uA, so the total current is 1.2 uA. If there is a sound input for an average of 10% of the time of the day, it is used in the low power mode for 90% of the time and in the normal power mode for 10% of the time. Based on 10% of the current consumption of 15.3 uA in normal power mode and 90% of the current consumption of 1.2 uA in low power mode, the average current consumption is 2.46 uA. Without the SAM function, the current consumption is 14.3 uA, and with the SAM function, the average current consumption is 2.46 uA, so the current consumption can be reduced by 83%. Table 1 summarizes the performance of the developed circuits and compares them with the results of the previous work. In 2020, [PERSON] et al. announced a microphone with a Sound Activity Detector (SAD) function [13]. This work and [PERSON]'s previous work are designed using the same CMOS 0.18 um process and have the same operating voltage of 1.8 V. Sound-activity monitoring features are designed to reduce microphone average power consumption in both this and previous works. As the architecture improves in this work, the current consumption is improved to 1 uA compared to the previous 2.5 uA.