SLOSEB7A September   2024  – October 2024 LOG300

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics Low Noise Amplifier (LNA) 
    6. 5.6 Electrical Characteristics Log Detector
    7. 5.7 Electrical Characteristics LNA + Log Detector (AFE)
    8. 5.8 Typical Characteristics: VCC = 5V
    9. 5.9 Typical Characteristics: VCC = 3.3V
  7. 6 Parameter Measurement Information
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Offset Correction Loop (OCL)
      2. 7.3.2 Single and Differential Input
      3. 7.3.3 Input Frequency Detect
    4. 7.4 Device Functional Modes
  9. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Ultrasonic Distance Measurement
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
        3. 8.2.1.3 Application Curves
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Third-Party Products Disclaimer
    2. 9.2 Receiving Notification of Documentation Updates
    3. 9.3 Support Resources
    4. 9.4 Trademarks
    5. 9.5 Electrostatic Discharge Caution
    6. 9.6 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

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発注情報

8.2.1.2 Detailed Design Procedure

The LOG300 supports a 5V VCC. Add a 10Ω and 10µF || 10nF close to the VCC pin to provide sufficient decoupling and immunity from external noise. This supply filter has a pole of 1.59kHz that is sufficiently less than the frequency of interest, which is 1MHz.

The absolute maximum voltage rating of pin LNA_In is ±1V. Add a back-to-back diode along with a series resistor (RS) at the input of the LNA (see also Figure 8-1). The back-to-back diode protects the LNA_In pin from being exposed to any high voltages, especially during the transmit operation. Choose the series resistance value in accordance to the maximum power rating (PMAX) of the back-to-back diode. The added series resistor contributes to the input noise and deteriorates the minimum input sensitivity.

Equation 2. R s   =   ( 0.7 V   ×   ( V m a x   -   0.7 V ) ) P m a x

The maximum expected output voltage of the LNA with a back-to-back diode placed at the input is:

Equation 3. 11 V/V   ×   0.7 V P   =   7.7 V P  

Since the LNA is only powered from a 5V supply; the maximum output is only 2.5VP.

The maximum input for the Log_Inp pin is 1.7VP for 5VCC (see also Section 5.1); therefore, add a band-pass filter (BPF) of appropriate attenuation in the pass-band region so that the detector block absolute maximum voltage rating is not violated. In this particular case, ensure that the BPF has an attenuation of at least −3.3dB. A BPF of −4.3dB is shown in Figure 8-1.

Choose an Offset_Cap value based on Section 7.3.1.

Choose the value of CF based on the required rise time of the Log_Out pin voltage (VLog_Out). A lower-value CF improves the rise time at the cost of higher ripple on the output envelope. For reference plots see also Section 5.8. Connect an oscilloscope at the Log_Out pin, triggered during the receive burst operation, to find the correct balance between the required rise time and the acceptable ripple.

The RF resistor decides the input-to-output slope. The value of RF in kΩ equals the input-to-output slope in mV/dB. In this example, calculate RF using the below set of equations:

Equation 4. S l o p e   m V / d B   =   R F   k Ω   =   ( S a t u r a t e d   o u t p u t   v o l t a g e   -   M i n i m u m   o u t p u t   v o l t a g e ) ( 20   x   l o g   ( M a x i m u m   L N A _ I n   -   M i n i m u m   L N A _ I n ) )  
Equation 5. S l o p e   mV/dB   =   ( 4.5 V   –   0.5 V ) ( 20   ×   l o g   ( 200 m V   -   6 µ V ) )
Equation 6. Slope (mV/dB) = 44mV/dB hence use RF kΩ = 44kΩ 
Note: The maximum and minimum Log_Out values have been relaxed to design for the output to operate well within the linear range.

The voltage measured at Log_Out can be traced back to calculate the input amplitude using the below equation:

Equation 7. Log_OutA= Slope x (Log_InALog_InB)+ Log_OutB
Equation 8. Log_InA=   (Log_OutA - Log_OutBSlope x Log_InB)

Where : A stands for values of Log_Out and Log_In at the required measurement point and B stands for Log_Out and Log_In values at a known input value measured during factory calibration or production.