Advanced Electronics: Concepts and Applications
Unused and Stuck States in Systems
Unused state: Not utilized in the main sequence.
Stuck state: Will not progress into the main sequence and prevents the system from reaching it.
Synchronous Counters
Advantages: Fewer errors occur due to the common clock at high-frequency counting.
- Avoid stuck states at power-up as it may not revert to the main sequence.
Advantages of synchronous counters over ripple counters: Ripple counters can only work in binary while synchronous counters work with other codes, e.g., Gray code.
Flash ADC
Operation: Produces a (e.g., 2-bit) number from comparator outputs. As the analog input exceeds the reference voltage (‘Vref’) at each comparator, the comparator outputs change to a ‘high’ state. The priority encoder then creates a binary number based on the highest-order input.
Resistor Chain: Voltages in the resistor chain are calculated as (Vref / total resistor values) * resistor value. Add the resistor value each time when moving up the chain.
Resolution: Increasing Vref increases the resolution.
Component Calculations:
- Number of resistors = 2^(number of bits)
- Number of comparators = (number of resistors) – 1
Speed: Flash converters are faster than successive approximation converters.
Thyristor
Operation: The anode must be positive with respect to the cathode. A small positive voltage must be supplied to the gate input. The thyristor acts as a latch and stays on even if the gate input is removed, allowing current to flow across the load even if ‘switch 1’ is opened again. A resistor is needed to protect the thyristor.
Resistor Calculation: R = V / I (use minimum voltage > Vsupply – Vgate / use minimum value of gate current)
Transistors vs. Thyristors: Transistors always dissipate power. Thyristors dissipate less power when used with a Zener diode and also act as a self-latching switch.
Advantages of Thyristors over Relays: Thyristors have no moving parts, so there are none to wear out.
Holding Current: The minimum anode/cathode current needed to maintain latching.
Capacitor Commutation
Thyristor OFF: P = 0V and load = 0V.
S1 Open: Q = Vs.
S1 Closed: P = 0V and load = Vs (thyristor conducts), but Q = still Vs.
S1 Opened: Thyristor latches ON.
S2 Closed: Q = Vs > 0V (Q must always be Vs higher than P), so P = 0V > -12V. Thyristor switches off, and a large current flows through the load, and P rises back to 0V.
S2 Opened Again: Pull-up resistor returns Q to 12V.
Diac: Fires a pulse to improve the rise time of the gate signal.
Phase Lag: Across the capacitor due to the change/discharge of the capacitor being slowed by the effect of the series resistor.
Voltage Drop: When on, the voltage across the thyristor (Vt) is ideally 0, so the load takes all the supply voltage.
Propagation Delay Calculation: For an 8-bit counter with a propagation delay of 80ns, the maximum frequency is calculated as follows: 80ns * 8 = 640ns; f = 1 / (640 * 10^-9) = 1.56MHz.
Power Supplies
Maximum Power: Pmax = (Vs^2) / (8 * RL), where Vs is the rail-to-rail voltage and RL is the load resistance.
Voltage Drop Across Transistor: 6.7V if Vin is 12V and resistors are the same.
Power Dissipated in Transistor: (Current through load in mA) * (voltage drop across transistor).
Input Impedance: Hfe * RL, where Hfe is the transistor’s current gain.
Voltage and Power Transfer
For maximum voltage transfer between two systems: The output impedance of system A should be 0 ohms.
For maximum power transfer: The output impedance of system A should be the same as the input impedance of subsystem B.
For maximum transfer of a voltage signal to a microphone: The input impedance of the preamplifier should be infinite.
Transistor Circuits
Output Voltage Calculation: Vout = (DCVin – 0.7V) / (voltage drop across transistor) = (Vin (top of rail) – Vout of previous stage).
Input Current Calculation: Current In = (DC mA) / Hfe.
Crossover Distortion: Occurs when the input voltage is between +0.7V and -0.7V, and neither transistor conducts, resulting in no voltage output.
Emitter Follower
Power Dissipation: No power is dissipated when no input signal is applied.
Summing Amplifier
Resistor Calculation: Ra = (Vin / output voltage) * binary value.
Bridge Circuits
Variable Resistor: A variable resistor in a bridge circuit takes into account differences in thermistors and allows Vout to be 0 at the same temperature.
Suitable Output Device: A center-zero voltmeter; positive deflection indicates the measured thermistor is colder, negative deflection indicates it is hotter.
Dummy Strain Gauge: Eliminates false readings due to temperature changes.
Strain Gauges
Resistance Variation: Strain gauges have different resistances when one is under a different strain compared to the other.
Temperature Compensation: V-out is resistant to temperature variation due to the dummy strain gauge.
DAC
Maximum Output Voltage: The maximum output voltage of a DAC is calculated as (Rf / Ri) * (sum of binary weighted inputs).
Active Filters
Gain: Active filters can have a gain greater than 1, while passive filters cannot.
Reactance and Resistance: The reactance of a capacitor is always the same as the resistor in an active filter.
Flat Band Gain: Flat band gain = Rf / Ri.
Frequency Response of Filters
When signal frequency increases:
- The reactance of the capacitor decreases.
- The resistance of the resistor remains the same.
- The voltage across the capacitor decreases.
- The voltage across the load increases.
Output Voltage: Output = (maximum input voltage) * gain.
PIC Microcontroller
Saving Working Register Contents: movfw WTEMP,1
Resetting External Interrupt Flag: bcf INTCON,1
Recovering Working Register from Wtemp: movfw Wtemp,0
Returning to Main Program: retfie
Importance of Saving Working Register: It is necessary to save the contents of the working register when starting an Interrupt Service Routine (ISR) because the working register may be used and its contents changed within the ISR.
Jumping to Interrupt Service Routine: goto ......
Checking for Reset Switch Press: btfss Port..,'0'
Reset Switch Handling: Checks if the reset switch is pressed. If so, it recovers the working register and returns to the main sequence; otherwise, it loops and repeats the sequence.
ISR Location: The microcontroller locates the ISR by reading the contents of the interrupt vector address 04.
Phase Shift
Calculation: Phase shift = tan^-1 (R / Xc), where R is the resistance and Xc is the capacitive reactance.
Binary Codes and False Readings
False Readings: Binary codes can produce false readings as a disc rotates and more than one segment changes. One segment changing first can cause a false reading. For example, a transition from 000 to 111 may be misinterpreted if the segments do not change simultaneously.
Emitter Follower and Line Regulation
Output Voltage Stability: The output voltage of an emitter follower remains unchanged as the voltage across the resistor changes to maintain a constant voltage (e.g., 7.5V) across the Zener diode.
Line Regulation: Changes in the supply voltage (Vs) cause V1 to increase, but the output voltage (Vs) remains unchanged due to the Zener diode regulation.
DC Output Calculation
Rectified Output: DC output = (Vrms * sqrt(2)) – 0.7V, where Vrms is the root-mean-square value of the AC input voltage.