High Speed, high common mode immunity communication interface
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Transcript of High Speed, high common mode immunity communication interface
HIGH SPEED, HIGH COMMON MODE IMMUNITY COMMUNICATION INTERFACE
Team May12-05
Chendong YangMengfei XuAdvisor: 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 restrictionLess than $3000.
3. Easy to useThe whole system should be easily setup and tested.
CONCEPTUAL SKETCH/ BLOCK DIAGRAM
Transmitter Comparator
V_pp = 300mVf = 10 MHz
USB Cable
SerialSignal
CLK
Same DataOut
CLK
Search in the current electronic market to see if we can find existing transmitter and receiver system that meet the requirement.
Market Search
Market Search ResultThere 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
PLAN
SCHEDULE SEMESTER I
SCHEDULE SEMESTER II
OUR CHOICE Transmitter:DS90C031 from National Semiconductor 1. Rising/Falling time: 1.5 ns2. input switching frequency support: excess 77 MHZ3. ~$34. ±350 mV differential signal
Receiver:LT 1711 from Linear Technology1. High common mode rejection : 65-75dB2. Rising/Falling time: 2ns3. Power supply range : 14 V4. Maximum input toggle frequency : 100 MHZ5. ~$5
TRANSMITTER PCB DESIGN
schematic
layout
Software: CadSoft EAGLE PCB design software
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 Vos2. Power supply : 5v3. Equipment used : function generator, oscilloscope, power supply and different kinds of cables4 load:100 ohm
V+
V-gnd
Schematic
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)
Output: two differential square wave with 320mv Vpp, and 1.24v Vos. the receiver could decode this signal
V+
V-
RECEIVER PSPICE SIMULATION
Differential square wave, Vp-p = 300mV, frequency = 10 MHzVdd = 11 V, Vss = 0V, and Vlatch = 0V.
RESULT I
Input: Differential Square wave, 300mVp-p, 10M Hz Common mode Voltage = 10 Vdc
• Top: Vout
• Bottom: Vin+(Green) Vin-(Pink)
RESULT II
• Input: Differential Square wave, 300mVp-p, 10M Hz• Common mode voltage changes linearly (PWL) from
0V to 10V
• Top: Vout
• Bottom: Vin+(Red) Vin-(Black)
RESULT III
• Input: Differential Square wave, 300mVp-p, 10M Hz• Common mode voltage changes sinusoidally from 0V and
10 V with 10M Hz.
• Top: Vout
• Bottom: Vin+(Blue) Vin-(Pink)
RECEIVER PCB DESIGN Software: CadSoft EAGLE PCB design
software
ACTUAL RECEIVER PCB
TEST I:
Vin +(Ramp signal): Vp-p = 600mV, common = 6 V and frequency = 10kHz;Vin -: DC = 6V;
Yellow: V+ inputBlue: V- inputPink: outputGreen: ~output
RESULT II
Vin +: DC = 6V;Vin -(Ramp signal): Vp-p = 600mV, common = 6V and frequency = 10kHz;
Yellow: V+ inputBlue: V- inputPink: outputGreen: ~output
RESULT III
Vin + (Square signal): Vp-p = 600mV, Common = 6V and frequency = 10 kHz;Vin - (Square signal): inverted Vin +.
Yellow: V+ inputBlue: V- inputPink: outputGreen: ~output
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
Input: Square wave, Vp-p = 3V, Frequency =1MHz;
Yellow: InputBlue: Output
Input: Square wave, Vp-p = 3V, Frequency =10 MHz;
Yellow: InputBlue: Output
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 COSTItem Approx. CostTransmitter Board ~$50Receiver Board ~$50Unexpected Cost(i.e. damaged board, chips, electronic)
~$20
Design Poster ~$20Total Cost ~$140
QUESTIONS?