# Question Regarding Capacitive Sensor IC

I have this Capacitive Sensor IC

I am trying to understand and analyze how to use this IC.

In the datasheet, on page 13 - Function description, it is mentioned as "There are four selectable non-harmonic sensor frequencies for generating the sensor driver output signal: 45.45 kHz, 71.43 kHz, 100 kHz and 125 kHz. This can be set in FREQ register (see 7.2.7)"

I am not able to understand the purpose of this frequency in the IC? For what purpose is the frequency?

Like, is this the frequency for the IC internal working derived from the CLK input from the Host or does this frequency available on any other pin of the which (like, can this frequency be measured external to the IC?)

My questions :

1. What does the frequency setting serve as? What is its purpose? From which section in the block diagram is this frequency generated from?

2. I couldn't find the "Sensor driver output" block on the block diagram? What is the sensor driver output and what does it do?

• Extremely sorry. My bad. Edited the question
– user220456
Commented Aug 5, 2020 at 16:59
• non harmonic frequencies are probably used to prevent interference from other capacitive sensors ... you could try treating the IC as a black box and use it without any knowledge of its internals Commented Aug 5, 2020 at 17:04

What does the frequency setting serve as? What is its purpose? From which section in the block diagram is this frequency generated from?

Capacitive sensors work by sending a waveform (in this case a sine wave) through a capacitor (might be air) and then sensing the change in voltage, and calculating a change in impedance. The frequency setting changes the frequency of the sine wave that the TX DAC outputs.

I couldn't find the "Sensor driver output" block on the block diagram? What is the sensor driver output and what does it do?

The sensor driver output is the 10 pins SEN[0:9] (sen 0 through 9) and this is what the impedance of what the chip is trying to measure is attached to. Source: https://www.mouser.in/datasheet/2/588/AMS_AS8579_Datasheet_V2_00-1853724.pdf

• Thank you for the answer. So, the mentioned frequencies of 45.45kHz to 125kHz is the output from the VAR_SEN pin? We will be able to measure the frequencies in the VAR_SEN pin right?
– user220456
Commented Aug 6, 2020 at 3:19
• As you mentioned, The sensor driver block is the 10 pins, which is actually an input multiplexer. And isn't it confusing, that why should one address or call the input MUX block as the Sensor driver output block (as the MUX accepts the signals as input from the outside of the IC and provides MUX output internal to the IC and then to the HOST controller using SPI lines) ? Shouldn't the Sensor driver block name be like, MUX input block?
– user220456
Commented Aug 6, 2020 at 3:23
• And, from the Block diagram, I was not able to see any MUX Selector input lines. From where is the MUX Selector input line provided? Is the MUX Selector input information is sent from the host controller to the IC via SPI Lines?
– user220456
Commented Aug 6, 2020 at 3:24