HIGH SPEED, HIGH COMMON MODE
IMMUNITY COMMUNICATION
INTERFACE
Team May12-05
Chendong Yang
Mengfei Xu
Advisor: Nathan Neihart
Client: RBC Medical Development
STATEMENT OF PURPOSE

Design a high speed low voltage differential signaling
communication interface that would be capable of a high common
mode immunity and high speed transmission.
Why is LVDS used?

LVDS signals have the characteristics of low-noise and fast
data rate
Why is high common mode voltage immunity needed?
 When the reference voltage changes from transmitter
and receiver, it can cause errors in output signal. It is
even important when transmitting patient critical
signals which need to be uninterrupted.
Vgound1=10v
Vgound2=0v
Normal
system
Our
System
FUNCTIONAL REQUIREMENTS




1. System is capable at least 20M bps
2. At least 10 Volts Common mode voltage immunity
3. TTL/CMOS input level signals in and same signals
out only with some amplitude modification.
4. The clock and associated circuitry will be
electrically isolated from the rest of the system
NON-FUNCTIONAL REQUIREMENTS
1. Stability,
The output of the system should be stable.

2. Budget restriction
Less than $3000.

3. Easy to use
The whole system should be easily setup and tested.

CONCEPTUAL SKETCH/ BLOCK DIAGRAM
V_pp = 300mV
f = 10 MHz
Same
Data
Out
Serial
Signal
Transmitter
CLK
USB Cable
Comparator
CLK
PLAN
Market Search
Search in the current electronic market to see if we
can find existing transmitter and receiver system
that meet the requirement.
Market Search Result
There are no such communication system existing
in the market. We need to build up our own boards
with proper driver and comparator chips in the
market, then test the results
SCHEDULE SEMESTER I
SCHEDULE SEMESTER II
OUR CHOICE

Transmitter:
DS90C031 from National Semiconductor
4.
Rising/Falling time: 1.5 ns
input switching frequency support: excess 77 MHZ
~$3
±350 mV differential signal

Receiver:
1.
2.
3.
LT 1711 from Linear Technology
1.
2.
3.
4.
5.
High common mode rejection : 65-75dB
Rising/Falling time: 2ns
Power supply range : 14 V
Maximum input toggle frequency : 100 MHZ
~$5
TRANSMITTER PCB DESIGN

Software: CadSoft EAGLE PCB design software
schematic
layout
ACTUAL TRANSMITTER PCB
SMA
connector
USB
Cable
TRANSMITTER TEST
Test environment
1. Input signal:1-10 MHZ 3 Volts Vpp square wave
with 1.5 Volts Vos
2. Power supply : 5v
3. Equipment used : function generator, oscilloscope,
power supply and different kinds of cables
4 load:100 ohm

Schematic
V+
Vgnd
LIMITATION ON TRANSMITTER TEST
The equipment in the lab which we can access
can only provide 10 MHz square wave for
testing. The test frequency is much less the
maximum capacity of the Transmitter which
could go above 77 MHz.
 The soldering skill we have not meet the
industry equipment, the system could increase
the mechanical stability with professional
soldering.
 No Pspice model are provided by the company,
we can not do the Pspice Test for Transmitter

RESULTS(LVDS OUTPUT FOR TRANSMITTER)
V+
V-
Output: two differential square wave with 320mv Vpp, and
1.24v Vos. the receiver could decode this signal
RECEIVER PSPICE SIMULATION
Differential square wave, Vp-p = 300mV, frequency = 10 MHz
Vdd = 11 V, Vss = 0V, and Vlatch = 0V.
RESULT I
• Top: Vout
• Bottom:
Vin+(Green)
Vin-(Pink)


Input: Differential Square wave, 300mVp-p, 10M Hz
Common mode Voltage = 10 Vdc
RESULT II
• Top: Vout
• Bottom:
Vin+(Red)
Vin-(Black)
• Input: Differential Square wave, 300mVp-p, 10M Hz
• Common mode voltage changes linearly (PWL) from 0V to
10V
RESULT III
• Top: Vout
• Bottom:
Vin+(Blue)
Vin-(Pink)
• Input: Differential Square wave, 300mVp-p, 10M Hz
• Common mode voltage changes sinusoidally from 0V and 10 V
with 10M Hz.
RECEIVER PCB DESIGN

Software: CadSoft EAGLE PCB design software
ACTUAL RECEIVER PCB
TEST I:
Yellow: V+ input
Blue: V- input
Pink: output
Green: ~output
Vin +(Ramp signal): Vp-p = 600mV, common = 6 V and frequency =
10kHz;
Vin -: DC = 6V;
RESULT II
Yellow: V+ input
Blue: V- input
Pink: output
Green: ~output
Vin +: DC = 6V;
Vin -(Ramp signal): Vp-p = 600mV, common = 6V and frequency = 10kHz;
RESULT III
Yellow: V+ input
Blue: V- input
Pink: output
Green: ~output
Vin + (Square signal): Vp-p = 600mV, Common = 6V and frequency = 10 kHz;
Vin - (Square signal): inverted Vin +.
LIMITATION ON RECEIVER


TEST:
Due to the limitations of equipment in the lab, we
cannot change the common mode voltage of the
differential signals linearly or sinusoidly as we
simulated in Pspice.
We manually change the common mode voltage
from 1 V up to 10 V, and there is not significant
distortion on output shape or frequency. We can
still distinguish the outputs correctly.
WHOLE SYSTEM TEST
Yellow: Input
Blue: Output
Input: Square wave, Vp-p = 3V, Frequency =1MHz;
Yellow: Input
Blue: Output
Input: Square wave, Vp-p = 3V, Frequency =10 MHz;
LIMITATION ON WHOLE SYSTEM TEST:
We cannot swing or change the common mode
voltage transmitting through USB cable
manually.
 But we did common mode voltage test in the
receiver test separately, it is sufficient to show
that our designed system has the ability to
transmitter 10 MHz and tolerate common mode
voltage up to 10 V change.

TOTAL COST
Item
Approx. Cost
Transmitter Board
~$50
Receiver Board
~$50
Unexpected Cost(i.e.
damaged board, chips,
electronic)
~$20
Design Poster
~$20
Total Cost
~$140
QUESTIONS?