SCBS881E January   2010  – October 2018 TMS3705


  1. 1Device Overview
    1. 1.1 Features
    2. 1.2 Applications
    3. 1.3 Description
    4. 1.4 Functional Block Diagram
  2. 2Revision History
  3. 3Device Characteristics
    1. 3.1 Related Products
  4. 4Terminal Configuration and Functions
    1. 4.1 Pin Diagram
    2. 4.2 Signal Descriptions
      1. Table 4-1 Signal Descriptions
  5. 5Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Electrical Characteristics
    5. 5.5 Thermal Resistance Characteristics for D (SOIC) Package
    6. 5.6 Switching Characteristics
    7. 5.7 Timing Diagrams
  6. 6Detailed Description
    1. 6.1  Power Supply
    2. 6.2  Oscillator
    3. 6.3  Predrivers
    4. 6.4  Full Bridge
    5. 6.5  RF Amplifier
    6. 6.6  Band-Pass Filter and Limiter
    7. 6.7  Diagnosis
    8. 6.8  Power-on Reset
    9. 6.9  Frequency Divider
    10. 6.10 Digital Demodulator
    11. 6.11 Transponder Resonance-Frequency Measurement
    12. 6.12 SCI Encoder
    13. 6.13 Control Logic
    14. 6.14 Test Pins
  7. 7Applications, Implementation, and Layout
    1. 7.1 Application Diagram
  8. 8Device and Documentation Support
    1. 8.1 Getting Started and Next Steps
    2. 8.2 Device Nomenclature
    3. 8.3 Tools and Software
    4. 8.4 Documentation Support
    5. 8.5 Community Resources
    6. 8.6 Trademarks
    7. 8.7 Electrostatic Discharge Caution
    8. 8.8 Export Control Notice
    9. 8.9 Glossary
  9. 9Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

Digital Demodulator

The input signal of the digital demodulator comes from the limiter and is frequency-coded according to the high- and low-bit sequence of the transmitted transponder code. The frequency of the input signal is measured by counting the oscillation clock for the time period of the input signal. As the high-bit and low-bit frequencies are specified with wide tolerances, the demodulator is designed to distinguish the high-bit and the low-bit frequency by the shift between the two frequencies and not by the absolute values. The threshold between the high-bit and the low-bit frequency is defined to be 6.5 kHz lower than the measured low-bit frequency and has a hysteresis of ±0.55 kHz.

The demodulator is controlled by the control logic. After the charge phase (that is during read or write phase) it measures the time period of its input signal and waits for the transponder resonance-frequency measurement to determine the counter state for the threshold between high-bit and low-bit frequency. Then the demodulator waits for the occurrence of the start bit. For that purpose, the results of the comparisons between the measured time periods and the threshold are shifted in a 12-bit shift register. The detection of the start bit comes into effect when the contents of the shift register matches a specific pattern, indicating 8 subsequent periods below the threshold immediately followed by 4 subsequent periods above the threshold. A 2-period digital filter is inserted in front of the 12-bit shift register to make a start bit detection possible in case of a nonmonotonous progression of the time periods during a transition from low- to high-bit frequency.

The bit stream detected by the input stage of the digital demodulator passes a digital filter before being evaluated. After demodulation, the serial bit flow received from the transponder is buffered byte-wise before being sent to the microcontroller by SCI encoding.