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TDC1000: A weird oscillation appeared in LNAOUT & PGAOUT

JJ Martin
Prodigy 130 points
Part Number: TDC1000

Here is the paranmeter setting up for TDC1000

TX_FREQ_DIV = 5;
NUM_RX = 0;
VCOM_SEL = 0;
DAMPING = 0;
CH_SEL = 0;
TOF_MEAS_MODE = 0;
BLANKING = 1; 
ECHO_QUAL_THLD = 4;
TX_PH_SHIFT_POS = 31;
PGA_GAIN = 7;
PGA_CTRL = 0;
LNA_CTRL = 0;
 LNA_FB = 1;
TIMING_REG = 800; 
 FORCE_SHORT_TOF = 0;
SHORT_TOF_BLANK_PERIOD = 0;
ECHO_TIMEOUT = 0;
TOF_TIMEOUT_CTRL = 3;
CLOCKIN_DIV = 1;
 AUTOZERO_PERIOD = 3;

And I have a problem is that the strange oscillation about 3.3MHz in after RX rising till whole echo listening

Although there is only figures had seen from compin pin，but it had appeared in LNAOUT , and it amplitude is about ten times bigger than PGAOUT (a one-step bandpass filter between PGAOUT&COMPIN)

  • 0
    TI__Expert 7599 points

    Hello User,

    Thanks for posting your question. The LNAOUT is the output of the first stage RX path. I would probe the input of the RX to confirm if there are any oscillation at the input. If the inputs are oscillating it most likely that the the LNAOUT is amplifying the input. If the inputs are noisy due to the grounding or disturbance due to the transducer. I recommend that you follow section 8.3.3 that describes the capacitance selection for providing the stability of the amplifier. 

  • 0 in reply to Arjun_Prakash
    Prodigy 130 points

    Hi , Prakash   thanks you for replying my question

    The RX exactly have the same noise(I disconnected all the trace before RX pin and derectly probe RX pin) , and I will try 8.3.3 that you suggested lately.

    Hope it can improve my signal ~

  • 0 in reply to JJ Martin
    TI__Expert 7599 points

    Hello, 

    Good luck in your debug! we are always here to help. Incase you need more information please fell free to review our FAQ. It does have most common debug steps and will guide you through any hurdles you may face.