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TLV320ADC3140: Single end input from microphone

Yuta Nishie
Genius 5005 points
Part Number: TLV320ADC3140

Tool/software:

Hi,

1. The signal from the microphone is input to INxP in a single end. I would like to know the circuit design of INxM in this case. A capacitor is installed in INxM as shown in Figure 31 in the datasheet. Is there a recommended constant value for this capacitor?

Currently, a capacitor with the same value as the capacitor connected to INxP is installed.

2. For single-end input, is it appropriate to set GPO_CFG0 [3:0] to 0d (disabled)?

3. Other than CH1_IMP [1:0], are there any other registers related to the frequency characteristics and signal-to-noise ratio of the input signal?

Best Regards,

Nishie

  • +1
    TI__Mastermind 46445 points

    Hi Nishie,

    1) 4.7uF is the recommended value. This is the value used on the EVMs.

    2) GPO settings having no impact on single ended vs differential configurations. The only thing that matters is the CHx_CFG0 config registers

    3) No there are no other register settings that would impact frequency or SNR, just the input impedance selected.

    Best regards,
    Jeff McPherson

  • 0 in reply to Jeff McPherson
    Genius 5005 points

    Hi Jeff-san,

    Thank you for your reply.

    Jeff McPherson said:
    1) 4.7uF is the recommended value. This is the value used on the EVMs.

    ->1. If I used a 100uF AC coupling capacitor and CH1_IMP [1:0] =20kΩ to form a high pass filter for INxP, is a 4.7uF capacitor recommended for INxM?

    2. Is there any operational risk if a capacitor with a value significantly larger than 4.7uF (for example, 100uF) is mounted?

    Jeff McPherson said:
    GPO settings having no impact on single ended vs differential configurations. The only thing that matters is the CHx_CFG0 config registers

    ->3. When using the CHx_CFG0 register, could you please tell us if there are any precautions regarding the use of Microphone input and Line input, and the difference in electrical characteristics?

    Best Regards,

    Nishie

  • +1 in reply to Yuta Nishie
    TI__Mastermind 46445 points

    Hi Nishie,

    The only consideration in cap choice is the high pass filter formed.

    1 / 2pi * 20k * 4.7u = 1.6Hz so this is fine.

    There's no additional risk by adding a larger cap size.

    There's no difference in electrical characteristics when using mic or line input. It's just a label for the user. 

    Best regards,
    Jeff McPherson

  • 0 in reply to Jeff McPherson
    Genius 5005 points

    Hi Jeff-san,

    1. In the case of single-end input, the high-pass filter is probably due to the capacitor input to the INxP pin and the input impedance.

    Could you confirm the recommended capacitance of the capacitor between the INxM pin that is not in use and the GND and the risk of selecting a capacitor with a large capacity?

    2. For example, whether I choose to input a signal directly from an ECM or MEMS microphone or from an amplifier, does the setting of the CHx_CFG0 register matter, and if I set the bias voltage and PGA in another register, will there be no problem in operation?

    Best Regards,

    Nishie

  • +1 in reply to Yuta Nishie
    TI__Mastermind 46445 points

    Hi Nishie-san,

    1) The capacitor between INxM and GND should ideally match the capacitor used between INxP and the MIC. This is for CMRR reasons.

    2) CHx_CFG0 does matter, but bit 7 does not matter. It has no impact. However when switching from MIC to AMP or AMP to MIC, the register will probably stay the same except for SE vs DIFF input. 

    Best regards,
    Jeff McPherson