In electronics direct coupling is a way of interconnecting two circuits such that, in addition to transferring the signal (or information), the first stage also provides DC bias to the next^ǂ. Thus, there is no need for a DC blocking capacitor to be used in order to interconnect the circuits, and this method is also known as DC coupling. This technique is used by default in circuits like IC op-amps, since large coupling capacitors cannot be fabricated on-chip. That said, even discrete circuits (such as power amplifiers) too employ direct coupling for improved low frequency performance. One advantage or disadvantage (depending on application) of direct coupling is that any DC at the input appears as a valid signal to the system, and so it will be transferred from the input to the output (or between two directly coupled circuits). If this is not a desired operation then the term used for the output signal is output offset error, and the corresponding input signal is known as input offset error. Temperature drift and device mismatches are the major causes of offset errors, and circuits employing direct coupling often integrate offset nulling mechanisms. Some circuits (like power amplifiers) even use coupling capacitors — except that these are present only at the input (and/or output) of the whole system but not between the individual circuit units inside the system. The advantage of direct coupling is very good low frequency response, often from DC (if the input/output coupling capacitors are not used) to the highest operating frequency that the system will allow. Most industrial applications that require monitoring of slowly changing signals (such as those from thermistors, thermocouples, etc.) must have a very good DC amplification with minimum offset errors and hence they have to be directly coupled throughout by default, and have offset correction or trimming incorporated into them. In electronics, capacitive coupling is the transfer of energy from one circuit to another by means of the mutual capacitance between the circuits. ... Integrated circuit showing memory blocks, logic and input/output pads around the periphery A monolithic integrated circuit (also known as IC, microchip, silicon chip, computer chip or chip) is a miniaturized electronic circuit (consisting mainly of semiconductor devices, as well as passive components) which has been manufactured in the surface... A 741 operational amplifier in a TO-5 metal can package An operational amplifier, often referred to as an op-amp, is a DC-coupled electronic differential voltage amplifier, usually of very high gain, with one inverting and one non-inverting input. ... An amplifier is a device which changes a small movement into a larger movement. ...

ǂ – This is only true for a group of circuits that forms a single unit, such as an op-amp. Here the internal units or portions of the op-amp (like the input stage, voltage gain stage, and output stage) will be direct coupled and will also be used to set up the bias conditions inside the op-amp (the input stage will also supply the input bias to the voltage gain stage, for example). However when two op-amps are directly coupled the first op-amp will not supply any bias to the next - any DC at its output will form the input for the next. The resulting output of the second op-amp now represents an offset error if it is not the intended one. A 741 operational amplifier in a TO-5 metal can package An operational amplifier, often referred to as an op-amp, is a DC-coupled electronic differential voltage amplifier, usually of very high gain, with one inverting and one non-inverting input. ...

See also

Capacitive coupling In electronics, capacitive coupling is the transfer of energy from one circuit to another by means of the mutual capacitance between the circuits. ...