Handbook for Sound Engineers

Tubes, Discrete Solid State Devices, and Integrated Circuits 363

Figure 12-76. Typical digital circuits and their characteristics for the major logic families. (Adapted from Reference 4.)

Symbol Circuit Diagram Speed* Power* Fan-Out* Noise Trade Remarks

Immunity* Name

DCTL Medium Medium Low Low Series 53

RTL Low Low Low Low RTL

RCTI Low Low Low Low Series 51

DTL Medium Medium Medium Medium 930

to high DTL

TTL High Medium Medium Medium SUHL

to high Series 54/74

CML High High High Medium MECL

(ECL) to high ECCSL

CTL High High Medium Medium CTML

I^2 L High Low High Medium I^2 L

Variations in input characteristics result in

base current “hogging” problems. Proper

operation not always guaranteed. More

susceptibile to noise because of low

operating and signal voltages.

Very similar to DCTL. Resistors resolve

current “hogging” problem and reduce

power dissipation. However,operating

speed is reduced.

Though capacitors can increase speed

capability, noise immunity is affected by

capacitive coupling of noise signals.

Use of pull-up resistor and charge-control

technique improves speed capabilities.

Many variations of this circuit exist, each

having specific advantages.

Very similar to DTL. Has lower parasitic

capacity at inputs. With the many

existing variations, this has become very

Similar to a differential amplifier, the

reference voltage sets the threshold

voltage. High-speed, high-fan-out oper-

ation is possible with associated high

power dissipation. Also known as

emitter-coupled logic (ECL).

More difficult manufacturing process

results in compromises of active device

characteristics and higher cost.

Provides smallest and most dense bipolar

gate. Simple manufacturing process and

higher component packing density than

the MOS process. Also known as

merged-transistor logic (MTL).

*Low = <5 MHz <5 mW <5 <300 mV

Medium = 5–15 MHz 5–15 mW 5–10 300–500 mV

High = >15 MHz >15mW >10 >500 mV

+V

+V

+V

+V

+V

C1

C2

+V

+V

+V