Chapter 3 Simulation

Transcription

1 Chapter 3 Simulation

2 Pulse Response Simulation [Single-end] (Setting) Pulse waves used in digital transmission include the fundamental frequency and its harmonics. Harmonics signals are easily emitted from a short transmission line on a printed circuit board and cause unwanted radiation. For this reason, techniques using chip beads and the like are employed to attenuate only the harmonic components while maintaining the quality of digital signals. Step1 Click the [Pulse Response Simulation-Single-end] button in the [Simulation/Tool] tab. Step3 Select MMZ1005B121C from the Product List for DUT. 28 Step2 Set such conditions as input waveform, damping resistance, driver, receiver, transmission line, and measurement point (The example below gives the default setting.). Step4 Click the [Simulate] button.

3 Pulse Response Simulation [Single-end] (Result) Result MMZ1005B121C With one chip bead, over/ undershoots are reduced. (Reference) MMZ1005D121C + Damping resistance (100 Ω) Combination with damping resistance reduces ringing and greatly attenuates the harmonic components. Damping resistance 29 Without filter (Reference) MMZ1005D121C Ringing occurs Transmission waveform Spectrum

4 Pulse Response Simulation [Differential] (Setting) In recent years, differential transmission systems have been adopted for high-speed serial transmission such as USB and HDMI. Differential transmission is resistant to external noise and helps improve high-speed transmission; however, such factors as its asymmetric transmission lines and skew (time lag of differential signals) generate common-mode components. A common-mode current, even though only a small current, causes a great amount of unwanted radiation; to reduce these factors common-mode filters are employed. Step1 Click the [Pulse Response Simulation-Differential] button in the [Simulation/Tool] tab. Step3 Select ACM P from the Product List for DUT. 30 Step2 Set such conditions as input waveform, output/input impedance, transmission line, and measurement point (The example below gives the default setting.). Step4 Click the [Simulate] button.

5 Pulse Response Simulation [Differential] (Result) Result ACM P Skew is reduced and transmission signals improved (only the common mode component is greatly reduced). 31 Without filter (Reference) MMZ1608R102A Chip beads are not suitable for differential transmission. Transmission waveform Transmission waveform (common mode component only)

6 TDR Simulation [Differential] (Setting) TDR (Time Domain Reflectometry) is a technique used to find the characteristic impedance of a circuit based on the reflected wave of the input step pulse. In particular, when signals of more than hundreds MHz are handled, transmission lines and components used are required to match as much as possible. Step1 Click the [TDR Simulation-Differential] button in the [Simulation/Tool] tab. Step3 Select ACM2012H-900-2P from the Product List for DUT. 32 Step2 Set such conditions as system impedance, input pulse (The example below gives the default setting.). Step4 Click the [Simulate] button.

7 TDR Simulation [Differential] (Result) Result ACM2012H-900-2P For high-speed differential transmission, the product nearly matches 100 Ω. Example: HDMI specifications 85 to 115 Ω 33 (Reference) Standard type

8 Inductor Temperature Rise Due to DC Current (Setting) In an inductor used for a power supply circuit, sometimes high DC current flows occur, and power is consumed by the inductor coil resistance, resulting in a rise of inductor temperature. The temperature rises in proportion to the square of current values; in actual use particular attention needs to be paid to this point. Step1 Click the [Other Simulations-Temperature Rise] button in the [Simulation/Tool] tab. Step3 Set the Ambient Temperature in the [Inductor] tab (For Heat Resistance and DC Resistance reference values of the selected product are automatically entered.). 34 Step2 Select VLC M from the Product List. Step4 Click the [Simulate] button. Heat Resistance refers to the temperature rise occurring when 1 W of electricity is consumed by the inductor. In other words, the smaller the value, the less the temperature is likely to rise with a large current flow.

9 Inductor Temperature Rise Due to DC Current (Result) Result 25 C 105 C 35 Ambient temperature : -20 C

10 Temperature Rise of Multilayer Ceramic Capacitor Due to AC Ripple Current (Setting) The impedance of a multilayer ceramic capacitor decreases as the frequency increases; therefore, with a large high-frequency current flow, the temperature of the capacitor rises. Particularly, when the capacitor is used as a smoothing capacitor after rectification, the temperature of the capacitor may sometimes rise due to the high ripple voltage; attention needs to be paid this point. Step1 Click the [Other Simulations-Temperature Rise] button in the [Simulation/Tool] tab. Step3 Set such conditions as power impedance in the [Capacitor] tab (For Heat Resistance the reference value of the selected product is automatically entered.). 36 Step2 Select C4532X5R1H155K from the Product List. Step4 Click the [Simulate] button. Heat Resistance refers to the temperature rise occurring when 1 W of electricity is consumed by the capacitor. In other words, the smaller the value, the less the temperature is likely to rise with a large current flow.

11 Temperature Rise of Multilayer Ceramic Capacitor Due to AC Ripple Current (Result) Result 200kHz 500kHz 37 Frequency : 100kHz

12 Electro-static Discharge Simulation (Setting) If several kv of voltage is instantly discharged as static electricity, this may result in the breakdown of LSI. Chip varistors are often used as a countermeasure. They are a nonlinear device and under normal conditions behave like a capacitor, but when a certain level of voltage or higher is applied, resistance suddenly decreases and current flows (refer to Chapter 2: Current vs. Voltage Characteristics of Chip Varistors). Insertion of this component between LSI and the ground, prevents LSI breaks due to the large current when a high voltage is applied. Step1 Click the [Other Simulations-Electro-static Discharge (Varistor)] button in the [Simulation/Tool] tab. Step3 Set the CR model (The example below gives the default setting.). 38 Step2 Select AVR-M1005C080MTAAB from the Product List. Step4 Click the [Simulate] button.

13 Electro-static Discharge Simulation (Result) Result Without filter High voltage is applied on the load. Chip varistor Voltage is substantially reduced. 39

14 NTC Thermistor Simulation (Setting) NTC thermistors are used as a temperature sensor, because their resistance varies according to the temperature (refer to Chapter 2: Resistance vs. Temperature Characteristics of NTC Thermistors). It is a general technique that the NTC thermistor is combined with several resistors, to which a voltage is applied, and from the changes of the output voltage a temperature is assessed. Step1 Click the [Other Simulations-NTC Thermistor] button in the [Simulation/Tool] tab. Step3 Set such conditions as circuit, input voltage, and resistance value (The example below gives the default setting.). 40 Step2 Select NTCG104BH103H from the Product List. Step4 Click the [Simulate] button.

15 NTC Thermistor Simulation (Result) Result A steeper gradient indicates better sensitivity to temperature. 5kΩ R1=1kΩ 41 20kΩ Max. Typ. Min.