Circuits Flashcards
Whether you have any silicon layout experience?. What happens if the capacitor is connected between the output and input nodes of the common source amplifier.
Effective input capacitance will increase by (1+gain) of the amplifier due to Miller effect
What is the difference between latches and flip-flops? What is the output of a flip-flop if the output is passed through an inverter and then fed back to the input?
Frequency is divided by 2
What is a PID Controller?
Proportional, Integral, and Derivative drive elements to control a process
What’s the difference between an electrolytic cap and ceramic? Describe appropriate application uses for each.
The main difference between ceramic and electrolytic capacitor is that, in ceramic capacitors, the two conductive plates are separated by a ceramic material whereas, in electrolytic capacitors, the two conductive plates are separated by an electrolyte and a metal oxide layer
Describe difference between voltage regulator, voltage leveler, and dc to dc converter?
Linear regulators can only be used to produce a lower voltage from a higher one
A level shifter is usually a part that converts digital signals from one logic standard to another
DC to DC converter converts a source of direct current (DC) from one voltage level to another
What is TTL Level?
TTL stands for Transistor-transistor logic a logic family built from bipolar junction transistors
Low:
0.0V to 0.8V
High:
2.4 to VCC
What CMOS Level?
Low:
0 V to 1/3 VDD
High:
2/3 VDD to VDD
Rectifier
an electrical device which converts an alternating current into a direct one by allowing a current to flow through it in one direction only.
Signal Integrity
Signal input is the same at the signal output
Methods
Digital Signal Integrity = Bit Error Rate = # of bits error / total bits received
Eye Diagram
- Amplitude, bit period, eye height, eye crossing percentage, eye height, eye width, jitter, rise time, fall time, one level, zero level
Boost Converter
Boost voltage input dependent on duty on the PWM of SW.
Parts
- Inductor
- Capacitor
- Diode
- Switch
- Voltage Source
Voltage Follower
Unity Gain Buffer - Signal input and output are the same but with high input impedance and low output resistance
Class A Amplifier
A linear amplifier biased so the active device conducts through 360 degrees of the input waveform.
Class B Amplifier
An amplifier with two active devices. The active components are biased so that each conducts for approximately 180 degrees of the input waveform cycle.
Class C Amplifier
An amplifier in which the active device conducts for less than 180 degrees of the input waveform cycle.
KCL
The algebraic sum of all currents entering and exiting a node must equal zero.
KVL
In a closed circuit, the sum of all source voltages must be equal to the sum of all voltage drops
Attenuate
Reduce amplification on signal
Common Blank Amplifier
Common refer to a place that is connected to both input and output
Aliased Signals
A signal (normally electrical) sampled below the Nyquist Rate (twice the maximum frequency content of the signal) so that the frequency content of signal is erroneously rearranged.
AC coupling
Circuit that passes an AC signal while blocking a DC voltage.
Amplitude
Magnitude or size of a signal voltage or current
What is time constant of for an RC circuit?
Time Constant Tau = R * C. Tau shows the relationship between the voltage across the capacitor with time and the current across the capacitor with time it takes to charge or discharge the capacitor
What is the amount of time for a capacitor to be fully charged?
5 Tau
What is the percentage of charged voltage Vc for 1 Tau?
63% Voltage of Source
When discharging the circuit what is the percentage of discharged voltage of 1 Tau?
37% Voltage of Source
Measuring Max Power in a circuit?
Measuring current go through the circuit because voltage tends to vary between different components
What is PCI and its specs?
The PCI bus resides on the system board and is normally used as an interconnect mechanism between highly integrated peripheral components, peripheral add-on boards, and host processor or memory systems.
Master-Slave relationship:
Master initiates read and write transaction
Host CPU is bus master, PCI Boards potentially claim the bus and become bus master
Main Characteristics
Synchronous
Transaction/Burst oriented
Bus mastering
Plug-and-play
Synchronous Clock - 33MHz Default and can go up to 66MHz for high speeds
PCI timing
PCI specifies timing related to its clock.
With a 33MHz clock, we have:
7ns/0ns Tsu/Th (setup/hold) constraint on inputs
11ns Tco (clock-to-output) on outputs
32 bit address
Bridge Chip to connect to CPU
PCI Spaces
Memory space
IO space
Configuration space
3.3, 5V Lines
PCI Express
Clock speed 2.5Gsps
Point to point bus
No line sharing is allowed
Clock recovery
Differential Pairs - more immune to external interferences, work at low voltages, helps clock recovery get precise signal transitions
Power Efficiency
(Vout * Iout) / (Vout * Iout + P)
P = Power Loss
How to get the voltage output of a buck converter or boost converter?
Need to get the partial change of current going through the circuit when the switch is off and on. Once you have the current for both you can add the two currents together and equate it o 0 since the net change of 1 full cycle of current of inductor is equal to 0. Then you can derive the Voltage output.
Purpose of the Flywheel diode
The setup is the diode is connected parallel to the inductor so when there is a huge negative voltage spike, the reverse current is allowed to flow to the diode and dissipate
What is special about enhancement mode MOSFETs?
Low On Resistance and high off resistance
What’s better to use to amplify a signal? BJT or MOSFET?
BJT is better because MOSFETs have low transconductance so the voltage gain will not be large.
Transconductance in MOSFET
Transconductance is derivative of Drain Current respect to VGS. Also know as gain
Driving I/O Pin using MOSFET, what should you consider?
Series resistor between gate and I/O pin to reduce max instantaneous I/O current when switching
Reduces effect of load switching which is coupled back to logic gate output but FET’s drain gate capacitance
Why does capacitor act like an open circuit?
When the capacitor is being charged, the Capacitor instantaneous current goes to 0 as time goes on.
How does a capacitor smooth voltage?
Provide a storage of energy which load can draw during times of transient high current
I = Cdv/dt
What is the gain of noninverting Amplifier?
G = 1 + R2 / R1
What are main rules of an ideal Op Amp?
- Infinite Input Impedance
- Infinite Open Loop Gain (Vin = (V+ - V-) / G)
- Input Difference = 0
How is a voltage follower setup?
V- is connected to the output of the op amp
What is the gain of an inverting amplifier
G = -R2/R1
Basic operation of a comparator
Vin > Vref => Vout = +VCC, Vin < Vref => Vout = -VCC
Why do MOSFETs have high input impedance?
There is no gate current so that is why there is high impedance => V = IZ. Gate is also highly capacitive
What happens when the drain and gate are connected on a MOSFET?
When The Drain and Gate of a MOSFET are connected together, A two-terminal device known as a ‘‘diode-connected transistor’’ results. if drain and gate is shorted then MOS will behave as a diode connected load and it will never go to triode region and can be used as resistive load offering a resistance equal to 1/gm. if drain and source is shorted then MOS capacitor in which SiO2 will behave as insulator. ie it is a resistor.
What graph describes the cutoff, saturation and triode modes of a MOSFET?
Ids vs Vds
Cutoff = Vgs > Vth => Ids = 0
Saturation = Vds >= Vgs - Vth
Triode = Vds<= Vgs - Vth
What happens when you apply voltage at the gate of the MOSFET?
The width of the Drain and Source changes along which charge carriers flow
What are the modes of BJT?
Cutoff = IB = 0
What are NPN and PNP Transistors?
NPN = E diode Forward bias face middle same with C
PNP = Diode Forward bias face E and Diode Forward Bias face C
Is I2C faster than SPI?
No SPI is faster and can go up to 10Mbps. I2C can only go hot to 400kbps
Difference between Flip Flop and Latches
Flip flop follows rising edge whereas Latches follow the voltage levels
