Recent advances in low voltage silicon germaniumand BiCMOS processes have allowed the design andproduction of very high speed amplifi ers. Because theprocesses are low voltage, most of the amplifi er designshave incorporated differential inputs and outputs to regainand maximize total output signal swing. Since many lowvoltageapplications are single-ended, the questions arise,“How can I use a differential I/O amplifi er in a single-endedapplication?” and “What are the implications of suchuse?” This Design Note addresses some of the practicalimplications and demonstrates specifi c single-endedapplications using the 3GHz gain-bandwidth LTC6406differential I/O amplifi er.
differential Nonlinearity: Ideally, any two adjacent digitalcodes correspond to output analog voltages that are exactlyone LSB apart. differential non-linearity is a measure of theworst case deviation from the ideal 1 LSB step. For example,a DAC with a 1.5 LSB output change for a 1 LSB digital codechange exhibits 1⁄2 LSB differential non-linearity. differentialnon-linearity may be expressed in fractional bits or as a percentageof full scale. A differential non-linearity greater than1 LSB will lead to a non-monotonic transfer function in aDAC.Gain Error (Full Scale Error): The difference between theoutput voltage (or current) with full scale input code and theideal voltage (or current) that should exist with a full scale inputcode.Gain Temperature Coefficient (Full Scale TemperatureCoefficient): Change in gain error divided by change in temperature.Usually expressed in parts per million per degreeCelsius (ppm/°C).Integral Nonlinearity (Linearity Error): Worst case deviationfrom the line between the endpoints (zero and full scale).Can be expressed as a percentage of full scale or in fractionof an LSB.LSB (Lease-Significant Bit): In a binary coded system thisis the bit that carries the smallest value or weight. Its value isthe full scale voltage (or current) divided by 2n, where n is theresolution of the converter.Monotonicity: A monotonic function has a slope whose signdoes not change. A monotonic DAC has an output thatchanges in the same direction (or remains constant) for eachincrease in the input code. the converse is true for decreasing codes.
ANALOG INPUT BANDWIDTH is a measure of the frequencyat which the reconstructed output fundamental drops3 dB below its low frequency value for a full scale input. Thetest is performed with fIN equal to 100 kHz plus integer multiplesof fCLK. The input frequency at which the output is −3dB relative to the low frequency input signal is the full powerbandwidth.APERTURE JITTER is the variation in aperture delay fromsample to sample. Aperture jitter shows up as input noise.APERTURE DELAY See Sampling Delay.BOTTOM OFFSET is the difference between the input voltagethat just causes the output code to transition to the firstcode and the negative reference voltage. Bottom Offset isdefined as EOB = VZT–VRB, where VZT is the first code transitioninput voltage and VRB is the lower reference voltage.Note that this is different from the normal Zero Scale Error.CONVERSION LATENCY See PIPELINE DELAY.CONVERSION TIME is the time required for a completemeasurement by an analog-to-digital converter. Since theConversion Time does not include acquisition time, multiplexerset up time, or other elements of a complete conversioncycle, the conversion time may be less than theThroughput Time.DC COMMON-MODE ERROR is a specification which appliesto ADCs with differential inputs. It is the change in theoutput code that occurs when the analog voltages on the twoinputs are changed by an equal amount. It is usually expressed in LSBs.
Calculation of the differential Impedance of Tracks on FR4 substrates
There is a discrepancy between calculated and measured values of impedance for differential transmission lineson FR4. This is especially noticeable in the case of surface microstrip configurations. The anomaly is shown tobe due to the nature of the substrate material. This needs to be considered as a layered structure of epoxy resinand glass fibre. Calculations, using Boundary Element field methods, show that the distribution of the electricfield within this layered structure determines the apparent dielectric constant and therefore affects theimpedance. Thus FR4 cannot be considered to be uniform dielectric when calculating differential impedance.
The SN65LBC170 and SN75LBC170 aremonolithic integrated circuits designed forbidirectional data communication on multipointbus-transmission lines. Potential applicationsinclude serial or parallel data transmission, cabledperipheral buses with twin axial, ribbon, ortwisted-pair cabling. These devices are suitablefor FAST-20 SCSI and can transmit or receivedata pulses as short as 25 ns, with skew lessthan 3 ns.These devices combine three 3-state differentialline drivers and three differential input linereceivers, all of which operate from a single 5-Vpower supply.The driver differential outputs and the receiverdifferential inputs are connected internally to formthree differential input/output (I/O) bus ports thatare designed to offer minimum loading to the buswhenever the driver is disabled or VCC = 0. Theseports feature a wide common-mode voltage rangemaking the device suitable for party-lineapplications over long cable runs.
The PCA82C250 and PCA82C251 are advanced transceiver products for use in automotive and general industrialapplications with transfer rates up to 1 Mbit/s. They support the differential bus signal representation beingdescribed in the international standard for in-vehicle CAN high-speed applications (ISO 11898). Controller AreaNetwork (CAN) is a serial bus protocol being primarily intended for transmission of control related data between anumber of bus nodes.
The TJA1042 is a high-speed CAN transceiver that provides an interface between aController Area Network (CAN) protocol controller and the physical two-wire CAN bus.The transceiver is designed for high-speed (up to 1 Mbit/s) CAN applications in theautomotive industry, providing the differential transmit and receive capability to (amicrocontroller with) a CAN protocol controller.
The TJA1051 is a high-speed CAN transceiver that provides an interface between aController Area Network (CAN) protocol controller and the physical two-wire CAN bus.The transceiver is designed for high-speed (up to 1 Mbit/s) CAN applications in theautomotive industry, providing differential transmit and receive capability to (amicrocontroller with) a CAN protocol controller.
為了在CDMA系統中更好地應用QDPSK數字調制方式，在分析四相相對移相（QDPSK)信號調制解調原理的基礎上，設計了一種QDPSK調制解調電路，它包括串并轉換、差分編碼、四相載波產生和選相、相干解調、差分譯碼和并串轉換電路。在MAX+PLUSⅡ軟件平臺上，進行了編譯和波形仿真。綜合后下載到復雜可編程邏輯器件EPM7128SLC84-15中，測試結果表明，調制電路能正確選相，解調電路輸出數據與QDPSK調制輸入數據完全一致，達到了預期的設計要求。
Abstract:
In order to realize the better application of digital modulation mode QDPSK in the CDMA system， a sort of QDPSK modulation-demodulation circuit was designed based on the analysis of QDPSK signal modulation-demodulation principles. It included serial/parallel conversion circuit, differential encoding circuit, four-phase carrier wave produced and phase chosen circuit, coherent demodulation circuit, difference decoding circuit and parallel/serial conversion circuit. And it was compiled and simulated on the MAX+PLUSⅡ software platform,and downloaded into the CPLD of EPM7128SLC84-15.The test result shows that the modulation circuit can exactly choose the phase，and the output data of the demodulator circuit is the same as the input data of the QDPSK modulate. The circuit achieves the prospective requirement of the design.
