RF Transmitter For Biological Signals

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RF Transmitter For Biological Signals

• ECE 453 Final Project
• Chia-Hsuan (Penny) Tsai,
• Benjamin Samuel Madoff,
• Idan Beck

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Project Proposal

• To design an instrumentation amplifier with RF
  transmitter specifically for recording and
  transmitting biopotential signals
• RF Transmitter
• Carrier Frequency 433 MHz
• Type Frequency Modulation

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Types of Biopotential Signals

• EEG electroencephalography
• EOG electrooculography
• EMG electromyography
• EKG/ECG electrocardiography

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RF Transmitter

• Input signal from electrodes amplified by
  instrumentation amp
• Analog voltage value fed to the Voltage
  Controlled Oscillator which produces the waveform
  to be transmitted
• Waveform fed into a power amplifier to power the
  signal so that it can drive the antenna to
  transmit the signal

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Instrumentation Amplifier
G
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Single Op Amp Benchmarks
Gain 91dB Bandwidth 1MHz
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Input Encryption for Transmission

• - Amplitude Modulation
• Involves superposition of two periodic functions
• Hard to maintain data integrity due to
  uncontrollable atmospheric variables.
• Frequency Modulation
• Involves converting an analog value to a
  frequency.
• Data integrity easier to maintain via clever
  circuit design for transmitter and receiver
  circuitry.

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Voltage to Frequency
Robert Moog, 1934 2005

• We used a Voltage Controlled Oscillator (VCO)
• An input voltage alters the reverse bias on a
  diode which acts as a tuning capacitor. This
  capacitor controls the oscillators resonant
  frequency and allows us to modulate the frequency
  through an input voltage.

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VCO Principles of Operation

• At a specific radian frequency,
  
• the tank behaves like a simple resistor. It then
  amplifies the input signal. It does not yet
  oscillate.
• - The tank also has a certain parasitic
  capacitance but as was shown in the final circuit
  its effect was negligible.

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VCO Principles of Operation
- This system amplifies its own noise at a
resonant frequency of the tank - All that it
takes is noise to start itself up. - This design
is very sensitive to power supply fluctuations
since the drain currents are a function of
Vdd Solution Differential design
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Our VCO Design
This design eliminates the dependency of the
drain currents on the voltage supply. Also the
common mode sense circuit minimized the swing
fluctuation due to fluctuating capacitances (will
be applicable with varactors). It also made a
very dependable current source with few
transistors. Now we need to make a VOLTAGE
controlled oscillator.
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Our VCO Design
We used varactors(reverse biased diodes) to
control the tank capacitance. This relation ship
is given below,
Where C0 is the junction capacitance at zero
bias, VR is the reverse-bias voltage, and fB is
the built in potential of the junction. We
removed the capacitor and used diodes as our main
tank capacitance for better control over carrier
frequency tuning through input signal bias.
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!Simulation Results!
Specifications Carrier Freq 433 MHz Tunability
38 (compared to 433MHz) Max amplitude
modulation 360 mV 5 Power Supply Modulation
effect on frequency 3 MHz .6
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Class E Power Amplifier
-The power amplifier drives the antenna -The
output power affects the transmission range
-Nonlinear Input only controls output
frequency. -Higher power efficiency -For short
distance transmissionthe output power is
2.8mW(or 4.476dBm)
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Concept of Class E PA
Simulation Result
Theoretical Result
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After set the switch
PIV
minimum
Id
Vd
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PA component parameters
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PA circuit
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Full Circuit Output
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Questions
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