Op Amp Digital to Analog Converter Circuit

This is a design of the simple 4-bit digital-to-analog converter.  It is actually just a variant of a simple op amp summer circuit, i.e., an operational amplifier configured to output a voltage that is proportional to the sum of the input voltages. Here’s the figure of the circuit;

In this circuit, the inputs are binary weighted with respect to each other, with the binary weighting of the inputs achieved by the R-2R ladder resistor network at the non-inverting input of the op-amp. As its name implies, the R-2R network consists of resistors with only two values, R and 2R (10K and 20K, respectively, in the circuit shown).  The input SN to bit N is '1' if it is connected to a voltage VR and '0' if it is grounded. The number of bits of this DAC may be increased by connecting more switches with corresponding R/2R resistors.

Op Amp Digital to Analog Converter Circuit

This is a design circuit for a simple 4-bit digital-to-analog converter.  It is actually just a simple op amp summer circuit, i.e., an operational amplifier configured to output a voltage that is proportional to the sum of the input voltages. This is the figure of the circuit;

The op-amp summer circuit above works as a DAC because its input voltages are binary weighted with respect to each other, as set by the resistors (10K, 20K, 40K, 80K) at the inputs.  
 
The output Vo of this summer circuit w is:    
Vo = -VRef (5K) (S3/10K + S2/20K + S1/40K + S0/80K) = -VRef (S3/2 + S2/4 + S1/8 + S0/16) wherein S3, S2, S1, and S0 are the logic inputs ('1' or '0'). The number of bits of this DAC may be increased by connecting more switches with corresponding binary-weighted resistors to the inputs.

Wien Bridge Oscillator Using CA3140

This is a bridge oscillator circuit. This circuit is excellent use of its high input impedance, high slew rate, and high voltage qualities and it is called the Wien Bridge sine wave oscillator. This is the figure of the circuit.


Oscillator stabilization takes on many forms. It must be precisely set, otherwise the amplitude will either diminish or reach some form of limiting with high levels of distortion. The element, RS, is commonly replaced with some variable resistance element. Thus, through some control means, the value of RS is adjusted to maintain constant oscillator output. A FET channel resistance, a thermistor, a lamp bulb, or other device whose resistance increases as the output amplitude is increased are a few of the elements often utilized. As the output signal amplitude increases, the zener diode impedance decreases resulting in more feedback with consequent reduction in gain; thus stabilizing the amplitude of the output signal. [Project Schematic source: Intersil Corporation].

Volume and Balance Controls Circuit Using Op Amp

The designed by Peter Baxandall of feedback tone control fame, amongst many other designs, there is also an active version of the 'Volume and Balance Control', which uses an op amp and a pot in the feedback loop. The log law is almost identical to that for the passive design above, but it can provide gain as well as attenuation. This circuit is using TL072 as op amp the signal input and output of the circuit. This is the figure of the circuit.


The input buffer enables the inverting stage (needed so the circuit can work) to have a very high input impedance. This would otherwise not be possible without the use of extremely high value resistors, which would increase the noise level considerably. The maximum gain as shown is 10 (20dB) and minimum gain is 0 (maximum attenuation). The input impedance is variable, and is dependent on the pot setting. At minimum gain, input impedance is the full 50k of the pot, falling to about 27k at 50% travel, and around 4k at maximum gain. These impedance figures are very similar to the simple passive version (if a 100k pot is used), and again, a low impedance drive is required or the logarithmic law will not apply properly. The actual value for VR1 does not matter, and anything from 10k to 100k will work just as well, although it will influence the input impedance. The error at 50% of pot travel is less than 5% with values from 10k to 100k.

Tuned Sine Wave Oscillator Circuit With Op Amp

This is a design circuit for sine wave oscillators that will provide both a sine and square wave output for frequencies from below 20 Hz to above 20 KHz. The frequency of oscillation is easily tuned by varying a single resistor. This circuit is controlled by two op amp, LM111 and LM101A. This is the figure of the circuit.


In this circuit, an operational amplifier has function as a tuned circuit, driven by square wave from a voltage comparator. The frequency is controlled by R1, R2, C1, C2, and R3, with R3 used for tuning. Tuning the filter does not affect its gain or bandwidth so the output amplitude does not change with frequency. A comparator is fed with the sine wave output to obtain a square wave. The square wave is then fed back to the input of the tuned circuit to cause oscillation. Zener diode, D1, stabilizes the amplitude of the square wave fed back to the filter input. Starting is insured by R6 and C5 which provide dc negative feedback around the comparator. This keeps the comparator in the active region. [Schematic diagram source: National Semiconductor. Inc]