Frequency divider

Last updated December 24, 2023

A frequency divider, also called a clock divider or scaler or prescaler , is a circuit that takes an input signal of a frequency, $f_{in}$ , and generates an output signal of a frequency:

Analog

Analog frequency dividers are less common and used only at very high frequencies. Digital dividers implemented in modern IC technologies can work up to tens of GHz.^{[ citation needed ]}

Regenerative

A regenerative frequency divider, also known as a Miller frequency divider,^[1] mixes the input signal with the feedback signal from the mixer.

The feedback signal is $f_{in}/2$ . This produces sum and difference frequencies $f_{in}/2$ , $3f_{in}/2$ at the output of the mixer. A low pass filter removes the higher frequency, and the $f_{in}/2$ frequency is amplified and fed back into the mixer.

Injection-locked

A free-running oscillator which has a small amount of a higher-frequency signal fed to it, will tend to oscillate in step with the input signal. Such frequency dividers were essential in the development of television.

It operates similarly to an injection locked oscillator. In an injection-locked frequency divider, the frequency of the input signal is a multiple (or fraction) of the free-running frequency of the oscillator. While these frequency dividers tend to be lower power than broadband static (or flip-flop-based) frequency dividers, the drawback is their low locking range. The ILFD locking range is inversely proportional to the quality factor (Q) of the oscillator tank. In integrated circuit designs, this makes an ILFD sensitive to process variations. Care must be taken to ensure the tuning range of the driving circuit (for example, a voltage-controlled oscillator) must fall within the input locking range of the ILFD.

Digital

For power-of-2 integer division, a simple binary counter can be used, clocked by the input signal. The least-significant output bit alternates at 1/2 the rate of the input clock, the next bit at 1/4 the rate, the third bit at 1/8 the rate, etc. An arrangement of flipflops is a classic method for integer-n division. Such division is frequency and phase coherent to the source over environmental variations, including temperature. The easiest configuration is a series where each flip-flop is a divide-by-2. For a series of three of these, such a system would be a divide-by-8. By adding additional logic gates to the chain of flip-flops, other division ratios can be obtained. Integrated circuit logic families can provide a single-chip solution for some common division ratios.

Another popular circuit to divide a digital signal by an even integer multiple is a Johnson counter. This is a type of shift register network that is clocked by the input signal. The last register's complemented output is fed back to the first register's input. The output signal is derived from one or more of the register outputs. For example, a divide-by-6 divider can be constructed with a 3-register Johnson counter. The six valid values of the counter are 000, 100, 110, 111, 011, and 001. This pattern repeats each time the input signal clocks the network. The output of each register is an f/6 square wave with 120° of phase shift between registers. Additional registers can be added to provide additional integer divisors.

Mixed signal

(Classification: asynchronous sequential logic )
An arrangement of D flip-flops is a classic method for integer-n division. Such division is frequency and phase coherent to the source over environmental variations, including temperature. The easiest configuration is a series where each D flip-flop is a divide-by-2. For a series of three of these, such a system would be a divide-by-8. More complicated configurations have been found that generate odd factors, such as a divide-by-5. Standard, classic logic chips that implement this or similar frequency division functions include the 7456, 7457, 74292, and 74294. (see list of 7400 series and list of 4000 series logic chips)

Fractional-N synthesis

A fractional-n frequency synthesizer can be constructed using two integer dividers, a divide-by-N, and a divide-by-(N + 1) frequency divider. With a modulus controller, N is toggled between the two values so that the VCO alternates between one locked frequency and the other. The VCO stabilizes at a frequency that is the time average of the two locked frequencies. By varying the percentage of time the frequency divider spends at the two divider values, the frequency of the locked VCO can be selected with very fine granularity.

Delta-sigma

If the sequence of divide by N and divide by (N + 1) is periodic, spurious signals appear at the VCO output in addition to the desired frequency. Delta-sigma fractional-n dividers overcome this problem by randomizing the selection of N and (N + 1) while maintaining the time-averaged ratios.

Related Research Articles

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A multivibrator is an electronic circuit used to implement a variety of simple two-state devices such as relaxation oscillators, timers, latches and flip-flops. The first multivibrator circuit, the astable multivibrator oscillator, was invented by Henri Abraham and Eugene Bloch during World War I. It consisted of two vacuum tube amplifiers cross-coupled by a resistor-capacitor network. They called their circuit a "multivibrator" because its output waveform was rich in harmonics. A variety of active devices can be used to implement multivibrators that produce similar harmonic-rich wave forms; these include transistors, neon lamps, tunnel diodes and others. Although cross-coupled devices are a common form, single-element multivibrator oscillators are also common.

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A dual modulus prescaler is an electronic circuit used in high-frequency synthesizer designs to overcome the problem of generating narrowly spaced frequencies that are nevertheless too high to be passed directly through the feedback loop of the system. The modulus of a prescaler is its frequency divisor. A dual-modulus prescaler has two separate frequency divisors, usually M and M+1.

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$<span class="mw-page-title-main">Voltage divider</span> Linear circuit that produces an output voltage that is a fraction of its input voltage$

In electronics, a voltage divider (also known as a potential divider) is a passive linear circuit that produces an output voltage (V_out) that is a fraction of its input voltage (V_in). Voltage division is the result of distributing the input voltage among the components of the divider. A simple example of a voltage divider is two resistors connected in series, with the input voltage applied across the resistor pair and the output voltage emerging from the connection between them.

A variable frequency oscillator (VFO) in electronics is an oscillator whose frequency can be tuned over some range. It is a necessary component in any tunable radio transmitter and in receivers that works by the superheterodyne principle. The oscillator controls the frequency to which the apparatus is tuned.

<span class="mw-page-title-main">Voltage-controlled oscillator</span> Electronic oscillator controlled by a voltage input

A voltage-controlled oscillator (VCO) is an electronic oscillator whose oscillation frequency is controlled by a voltage input. The applied input voltage determines the instantaneous oscillation frequency. Consequently, a VCO can be used for frequency modulation (FM) or phase modulation (PM) by applying a modulating signal to the control input. A VCO is also an integral part of a phase-locked loop. VCOs are used in synthesizers to generate a waveform whose pitch can be adjusted by a voltage determined by a musical keyboard or other input.

In electronic instrumentation and signal processing, a time-to-digital converter (TDC) is a device for recognizing events and providing a digital representation of the time they occurred. For example, a TDC might output the time of arrival for each incoming pulse. Some applications wish to measure the time interval between two events rather than some notion of an absolute time.

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In electronics, a frequency multiplier is an electronic circuit that generates an output signal and that output frequency is a harmonic (multiple) of its input frequency. Frequency multipliers consist of a nonlinear circuit that distorts the input signal and consequently generates harmonics of the input signal. A subsequent bandpass filter selects the desired harmonic frequency and removes the unwanted fundamental and other harmonics from the output.

In electronics, a delay-locked loop (DLL) is a pseudo-digital circuit similar to a phase-locked loop (PLL), with the main difference being the absence of an internal voltage-controlled oscillator, replaced by a delay line.

A ring counter is a type of counter composed of flip-flops connected into a shift register, with the output of the last flip-flop fed to the input of the first, making a "circular" or "ring" structure.

A frequency synthesizer is an electronic circuit that generates a range of frequencies from a single reference frequency. Frequency synthesizers are used in many modern devices such as radio receivers, televisions, mobile telephones, radiotelephones, walkie-talkies, CB radios, cable television converter boxes, satellite receivers, and GPS systems. A frequency synthesizer may use the techniques of frequency multiplication, frequency division, direct digital synthesis, frequency mixing, and phase-locked loops to generate its frequencies. The stability and accuracy of the frequency synthesizer's output are related to the stability and accuracy of its reference frequency input. Consequently, synthesizers use stable and accurate reference frequencies, such as those provided by a crystal oscillator.

<span class="mw-page-title-main">Texas Instruments SN76477</span> Sound generating integrated circuit

SN76477 "complex sound generator" is a sound chip produced by Texas Instruments (TI). The chip came to market in 1978, and TI ceased production of the part. A compatible version is identified as ICS76477. The chip is typically used as a sound effects generator in arcade games and toys and for hobby projects. The use of the SN76477 in a musical context is limited by the fact that it was difficult to electronically control the pitch of the produced sound.

A PLL multibit or multibit PLL is a phase-locked loop (PLL) which achieves improved performance compared to a unibit PLL by using more bits. Unibit PLLs use only the most significant bit (MSB) of each counter's output bus to measure the phase, while multibit PLLs use more bits. PLLs are an essential component in telecommunications.

In electronics, flip-flops and latches are circuits that have two stable states that can store state information – a bistable multivibrator. The circuit can be made to change state by signals applied to one or more control inputs and will output its state. It is the basic storage element in sequential logic. Flip-flops and latches are fundamental building blocks of digital electronics systems used in computers, communications, and many other types of systems.

References

↑ R. L. Miller (1939). "Fractional Frequency Generators Utilizing Regenerative Modulation". Proceedings of the IRE. 27 (7): 446–457. doi:10.1109/JRPROC.1939.228513.

External links

Digital frequency dividers

Divide by 2, and asynchronous 2^N Ripple Counter dividers - Electronics Tutorials
Synchronous divide by 3, 6, 9, 12 with 50% duty cycle output - ON Semiconductor
Synchronous divide by 3 or 5 with 50% duty cycle output, and divide by 1.5 & 2.5 circuits - Xilinx
Divide by N-0.5 using 74x161 counters - Whitepaper

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[1] R. L. Miller (1939). "Fractional Frequency Generators Utilizing Regenerative Modulation". Proceedings of the IRE. 27 (7): 446–457. doi:10.1109/JRPROC.1939.228513.

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