Logic dividers are integrated circuits (ICs) that divide the frequency of an input signal by a division ratio. There are two basic types of logic dividers: fixed dividers and programmable dividers. Fixed dividers have a division ratio that users cannot change. By contrast, programmable dividers can be programmed to use any division ratio up to a maximum limit. Both types of logic dividers are used in a variety of electronics applications as frequency synthesizers. In phased locked loops (PLLs), logic dividers receive input signals from voltage-controlled oscillators, divide signals by a division ratio, and send outputs to a phase comparator. For example, a divide-by-two circuit provides one output for every two inputs. For non-truncated dividers, the number of bits or stages is 2n, where n is the number of flip-flops (bits) in the divider.
Logic dividers vary in terms of supply voltage, operating current, clock frequency, and power dissipation. Supply voltages range from - 5 V to 5 V and include intermediate voltages such as -4.5 V, -3.3 V, -3 V, 1.2 V, 1.5 V, 1.8 V, 2.5 V, 3 V, 3.3 V, and 3.6 V. The operating current is the minimum current needed for active chip operation. The clock frequency is the highest clock rate in hertz at which the device can operate reliably. Power dissipation, the total power consumption of the device, is generally expressed in watts or milliwatts. Some logic dividers are radiation-tolerant. Others provide protection against electrostatic discharge (ESD).
Selecting logic dividers requires an analysis of logic families. Transistor-transistor logic (TTL) and related technologies such as Fairchild advanced Schottky TTL (FAST) use transistors as digital switches. By contrast, emitter coupled logic (ECL) uses transistors to steer current through gates that compute logical functions. Another logic family, complementary metal-oxide semiconductor (CMOS), uses a combination of p-type and n-type metal-oxide-semiconductor field effect transistors (MOSFETs) to implement logic gates and other digital circuits. Logic families for logic dividers include cross-bar switch technology (CBT), Gallium arsenide (GaAs), integrated injection logic (I2L) and silicon on sapphire (SOS). Gunning with transceiver logic (GTL) and gunning with transceiver logic plus (GTLP) are also available.
Logic dividers are available in a variety of IC package types and with different numbers of pins and flip-flops. Basic IC package types for logic dividers include ball grid array (BGA), quad flat package (QFP), single in-line package (SIP), and dual in-line package (DIP). Many packaging variants are available. For example, BGA variants include plastic-ball grid array (PBGA) and tape-ball grid array (TBGA). QFP variants include low-profile quad flat package (LQFP) and thin quad flat package (TQFP). DIPs are available in either ceramic (CDIP) or plastic (PDIP). Other IC package types include small outline package (SOP), thin small outline package (TSOP), and shrink small outline package (SSOP).
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