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Square Wave Generation Error with Stm32

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uranyumx

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Hello,

I have tried to generate square wave signals with TMUX1122DGKR switch. Basically, the stm32 feeds two analog signals from its internal DAC, the switch generates square pulses based on SET and RESET commands. But at the output signals, there is an extra 250 mV pulses on the blue signals. I didn't understand why it happened. Do you have any suggestion on that?

Thank you,

Code:
while (1)
  {
    /* USER CODE END WHILE */

    /* USER CODE BEGIN 3 */

      // Stimulation Voltage Signal Generation

      DAC1_Out = DAC1_Buf*(4096)/3.3;
      HAL_DAC_SetValue(&hdac, DAC_CHANNEL_1, DAC_ALIGN_12B_R, DAC1_Out);
      //HAL_Delay(1);
      HAL_DAC_SetValue(&hdac, DAC_CHANNEL_2, DAC_ALIGN_12B_R, DAC1_Out);

      //delay_us(200);
      HAL_GPIO_WritePin(PHASE_SEL_1_GPIO_Port, PHASE_SEL_1_Pin, GPIO_PIN_SET);
      delay_us(200);
      HAL_GPIO_WritePin(PHASE_SEL_1_GPIO_Port, PHASE_SEL_1_Pin, GPIO_PIN_RESET);
      delay_us(100);
      HAL_GPIO_WritePin(PHASE_SEL_2_GPIO_Port, PHASE_SEL_2_Pin, GPIO_PIN_SET);
      delay_us(200);
      HAL_GPIO_WritePin(PHASE_SEL_2_GPIO_Port, PHASE_SEL_2_Pin, GPIO_PIN_RESET);
      delay_us(400);

IMG_3556.jpg
 

Hello!

I don't understand the purpose, but OK, you might have your reasons.
The analog multiplexer has 2 inputs S1, S2, 2 outputs D1, D2, and 2 selections SEL1, SEL2.
When selected, S1 = D1, S2 = D2, which is the signals you observe. But when not selected,
D1 and D2 are connected to nothing, therefore the impedance is high and it can be influenced
by anything, for example if there is another signal in the neighborhood (and there is one).
Try to setup pulldown resistors at the outputs. For example 10k.

Dora.
 

Thank you very much @doraemon for your comments! It was worked with connecting 2 kOhms pull down resistors. So the placing these resistors at the outputs short any unwanted signal on the trace to the ground?

@KlausST , here is the schematic,
 

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