Digital to Analog with R2R Ladder Network
This is a R-2R Digital to Analog Converter, It converts a byte (8 bit) to a analog value. It has 256 levels including zero.
This was the first Digital Pot i Built decades back – Digital Potentiometer
This can be used to convert a byte sent from a microcontroller to a analog value like say 1.51 V. At full scale, when all 8 bits are high calibrate to give 2.55 V then ever bit increment is 0.01V, 10mV steps.
If the eight bits inputs are from a counter you then will see a staircase waveform at output, each step being 10mV higher or lower depending on whether the counter is counting up or down.
The accuracy of the analog output depends on the resistor ladder. The OP07 has an offset error of about 70uV only. The 74HCT373 power is derived from LM336 a stable reference so that the D-A is accurate. The 8 bit data can be latched with the 74HCT373 to get a stable analog value for control systems.
See another circuit in which both these ICs are used Mini RTD Pt-100 Three Wire Transmitter
OP07E has very low input offset voltage 75 µV max and low input bias current ±4 nA