Inverting Amplifier Circuit

Inverting Amplifier

• Output is applied back to the inverting input through the feedback circuit formed by Resistor input (R1) and Resistor feedback (Rf)
• Creates negative feedback using R1 and Rf as a voltage divider circuit
• Voltage divider reduces Voltage out (Vout) and connects the reduced feedback voltage to the inverting input
• For equal resistors, the circuit has a gain of -1 and is used in digital circuits as an inverting buffer (also known as an inverter)
• An op-amp inverting amplifier with a gain of 1 serves as an inverting buffer

Digital-to-Analogue Conversion (DAC)

• Digital-to-Analogue Converters (DAC) convert digital numbers into analogue voltage values
• Digital input values are input to the op-amp via weighted resistors
• The resultant voltage from the resistors is applied to the inverting input of the op-amp
• Binary weighted resistor DAC circuit uses +5 volts as a logic 1 and 0 volts as a logic 0

Binary Weighted Resistor DAC

• The circuit uses a 4-bit binary number and converts it into an analogue voltage
• The digits 1, 2, 4, and 8 refer to the relative weights assigned to each input
• The output voltage will take on one of 10 specific voltages in accordance with the input BCD code
• Input voltages are accurately 0 and +5 volts
• Output voltage will be -1, -2, -4, or -8 V depending on the input

R/2R Ladder DAC

• Overcomes the issue of large differences in resistor values between the LSB and MSB in binary weighted resistor DACs
• R/2R ladder construction maintains the correct ratios even when temperature varies

Non-Zero Level Detection

• Zero-level detector can be modified to detect voltages other than zero by connecting a fixed reference voltage to the inverting input
• The reference voltage can be set using a battery, voltage divider, or Zener diode
• As long as the input voltage exceeds the reference voltage, the output goes to its maximum positive voltage

Non-Inverting Amplifier

• An op-amp is connected in a closed-loop configuration as a non-inverting amplifier with a controlled amount of voltage gain
• The input signal is applied to the non-inverting input (Vin +)
• The output is applied back to the inverting input (negative -) through the feedback circuit formed by Resistor input (R1) and Resistor feedback (R2)

Flash ADC

• Uses a comparator and a DAC to convert analogue voltage to digital output
• The number of comparators required increases exponentially with the number of binary bits used to store the code
• Flash ADC encoder uses a set of Exclusive-OR (XOR) gates to realise the highest-order-input selection effect
• A simpler, non-priority encoder can be used due to the sequential comparator output states

Digital-Ramp ADC

• A slower but less expensive approach to ADC conversion
• Uses a DAC and a single comparator
• A binary counter is used as the register, and the clock increments the counter one step at a time until the comparator output (Vax) ≥ the ADC input (Va)
• It is called a digital-ramp ADC because the waveform at Vax is a step-by-step ramp