CD4046 Texas Instruments – Clock/Timing

Extract

The CD4046 is a CMOS micropower phase-locked loop (PLL) integrated circuit (IC) manufactured by Texas Instruments.

Summary

The CD4046 is a CMOS micropower phase-locked loop (PLL) integrated circuit (IC) manufactured by Texas Instruments. Introduced in the 1970s, the CD4046 has become notable for its versatility in a variety of applications requiring phase-locked loop functionality, such as frequency synthesis, modulation, and motor speed control. The chip features a built-in voltage-controlled oscillator (VCO) and multiple phase comparators, which enable precise control and synchronization of signal phases and frequencies. Historically, the development of the CD4046 and similar PLL systems was driven by the demand for fast frequency changes over wide ranges, particularly in communication receivers. These systems often incorporated a combination of mixers and PLLs to achieve rapid tuning capabilities, highlighting the importance of phase-locked loops in modern electronics. The design and understanding of PLLs have been significantly influenced by experts like Floyd M. Gardner, who emphasized the need for advanced control systems and filters to ensure effective operation. Key specifications of the CD4046 include a supply voltage range of 3 to 15 volts, an operating temperature range of -55°C to 125°C, and a 5.2-V Zener diode for supply regulation. The IC is available in various packaging types to suit different design needs, and it features an inhibit function for the VCO, which enhances its utility in precision applications. The CD4046’s compact dimensions make it suitable for integration into tight spaces, further adding to its appeal in both commercial and hobbyist projects. Despite its widespread use and numerous advantages, the CD4046 does have limitations. Users must be mindful of design considerations such as decoupling, pull-up or pull-down requirements, and the appropriate selection of loop filter components to avoid issues like slow ramp-up times or instability. Additionally, variations between manufacturers’ implementations of similar ICs, like the 74HC4046, can affect performance and necessitate careful tuning. Nevertheless, the CD4046 remains a popular and essential component in the field of electronic circuit design.

History

Back in the 70s, there was a demand for receivers that needed very fast frequency change capability over a wide frequency range. To meet this demand, a combination of mixers and phase-locked loops (PLLs) was employed instead of relying on a single PLL

. These systems were quite complex, sometimes even using digital storage and restoration of Automatic Gain Control (AGC) to achieve the required speed. The design and understanding of PLLs owe much to experts like Floyd M. Gardner, who has been a pivotal figure in this field. Gardner emphasized that a Type 2 PLL must have at least a second-order transfer function, which typically requires an active loop controller or filter when using a standard Phase-Frequency Detector (PFD). However, when employing a charge-pump PFD, a passive filter suffices, as illustrated by sourcecharge’s schematic and G0HZU’s mention of a “‘post PFD’ current sink/source circuit”. In addition to these technical advancements, the 1970s also saw educational contributions from industry experts. For instance, Leo Taylor significantly influenced the author’s understanding of audio circuits during this period. These foundational teachings and ongoing collaborations with mentors like Bill Eppler and Julia Truchsess have facilitated the development of various modern electronic projects, including the Null Tester and guitar-controlled synthesizers. Thus, the history of CD4046 and related technologies encapsulates a blend of innovative design solutions and educational mentorship that has propelled advancements in electronic circuit design from the 1970s to the present day.

Specifications

The CD4046 is a CMOS micropower phase-locked loop manufactured by Texas Instruments. This integrated circuit (IC) is designed for a variety of applications requiring phase-locked loop (PLL) functionality.

Features and Pinout

The CD4046 includes several key features that make it suitable for diverse applications. Notably, it contains a 5.2-V Zener diode for supply regulation, if needed

. The pinout of the CD4046 is critical for understanding its functionality. VSS represents the ground voltage, while VDD represents the supply voltage. The configuration of each pin is provided to help users understand the major functions associated with each pin on the chip.

Absolute Maximum Ratings

The absolute maximum ratings for the CD4046 must be adhered to avoid damage to the device. The DC supply voltage ranges between -0.5 to 18 volts, although it is recommended to keep the DC supply between 3 to 15 volts for optimal performance. The recommended operating temperature range is between -55°C to 125°C

Dimensions

The CD4046 is characterized by its compact dimensions, which make it ideal for fitting into tight spaces. The dimensions are provided in both inches and millimeters for accuracy and convenience

Applications

The CD4046 from Texas Instruments is a versatile integrated circuit that finds applications in various fields due to its flexible phase-locked loop (PLL) functionality and voltage-controlled oscillator (VCO).

Signal Generation

The CD4046 is widely used in musical synthesizers, testing instruments, and other applications requiring the generation of variable-frequency signals. Thanks to its built-in VCO, the CD4046 can produce output signals with frequencies controlled by an input voltage, allowing for dynamic adjustments as needed in various scenarios

Phase Detection

One of the critical functions of the CD4046 is phase detection. It can detect phase differences between two signals, which is valuable in electronic control systems and optical alignment systems. Phase synchronization is crucial in these applications to ensure that different components of a system operate in harmony

Frequency Tracking

The CD4046 is also used in frequency tracking applications, where it monitors frequency variations in an input signal and generates an output signal proportional to these changes. This feature is beneficial in frequency control applications, ensuring that systems remain within desired operational parameters even when input signals fluctuate

Historical Use in Communication Systems

In the 1970s, fast frequency change capability over a wide range was essential for certain receivers, especially in communication systems. Multiple PLLs, including the CD4046, were employed to achieve this functionality. These systems often included mixers and PLLs to perform the required tasks, sometimes even incorporating digital store and restore mechanisms for Automatic Gain Control (AGC) to achieve the necessary speed

Circuit Emulation and Testing

The CD4046 is often used in circuit emulation and testing scenarios. For instance, in LTspice emulations, common 2N3904 transistors might be used alongside the CD4046 to generate logarithmic results for voltage-controlled filters, although in practical circuits, dual NPN transistors are preferred for better linearity

Voltage-Controlled Filters

The CD4046’s capabilities extend to voltage-controlled filters used in synthesizers and other signal processing applications. This circuit adaptation, as noted in Texas Instruments Application Note AN-30, ensures that the voltage-controlled filter operates efficiently and accurately by maintaining consistent temperature conditions for the transistors involved

Packaging

The CD4046B variants of this IC are supplied in different packaging types to cater to various needs. These include 16-lead hermetic dual-in-line ceramic packages (F3A suffix), 16-lead dual-in-line plastic packages (E suffix), 16-lead small-outline packages (NSR suffix), and 16-lead thin shrink small-outline packages (PW and PWR suffixes)

Performance and Compatibility

The internal voltage-controlled oscillator (VCO) of the CD4046 has an inhibit function controlled through pin 5. The phase comparator 1 contains an exclusive OR gate. The output of the XOR gate (pin 2) is connected directly to the inhibit pin (pin 5), configuring the XOR gate as an inverting buffer

. The CD4046 ICs exhibit different levels of compatibility with various designs based on their VCO linearity specifications. Brands such as Fairchild’s CD4046 and Motorola’s MC14046 have been found to tune more easily and consistently.

Functionality

The CD4046 is a versatile integrated circuit (IC) commonly used for phase-locked loop (PLL) applications. The PLL configuration within the CD4046 consists of several key components: a phase detector, a voltage-controlled oscillator (VCO), and a loop filter, which work together to synchronize the phase and frequency of an input signal with a reference signal

Phase Detector Section

The phase detector is a crucial component of the PLL, responsible for comparing the phase of the input signal with that of the VCO. The CD4046 features multiple subcircuits and models to simulate the behavior of the phase detector and related components. These include various logic gates such as NAND, XOR, D-type flip-flops, AND, BUFA, ANDA, DLYLINE, and BUFB, each configured with specific timings and parameters for accurate simulation

. This section generates a signal proportional to the phase difference between the input and reference signals, which is then passed through a loop filter to remove unwanted signals .

Voltage-Controlled Oscillator (VCO)

The VCO in the CD4046 is responsible for generating an output signal whose frequency is controlled by an input voltage. The VCO section includes various components like resistors, voltage multipliers, and switches that are used to control the oscillation frequency. For instance, the model “swt” represents a voltage-controlled switch used to simulate the switching behavior in the circuit

. The resulting error signal from the phase detector is applied to the input of the VCO, which adjusts its frequency to match that of the input signal .

Timing Models and Stimulus Source

Accurate timing is essential for the proper functioning of the CD4046. Various subcircuits, such as NAND_TIMING, DFF1_TIMING, and BUFA_TIMING, are configured with specific timing parameters to replicate the behavior of the corresponding logic components accurately

. Additionally, a stimulus source named “Ureset” generates a reset signal for simulation purposes, switching from an initial value of 0 to 1 after 2 nanoseconds and maintaining this state thereafter .

Practical Applications

The CD4046 has found extensive use in numerous projects over the last several decades, primarily due to its superior phase comparator sections

. It is often used in tuning modern-day receivers, such as cell phones, AM/FM receivers, communication receivers, and TV sets, where the local oscillator and consequently the receiver are tuned using the PLL configuration . Moreover, it can also be utilized to build voltage-controlled oscillators (VCOs) for generating clock signals required by various digital circuits .

Performance Parameters

The performance parameters of the CD4046 include several critical factors that influence its operation and effectiveness in various applications. Key parameters include lock time, divider noise, phase-frequency detector (PFD) frequency, DM prescaler ratio, synth step size, reference sideband levels, and VCO noise. Balancing these factors is essential to achieving optimal performance across a wide tuning range

Lock Time and Divider Noise

Lock time and divider noise are crucial considerations when designing systems using the CD4046. Proper tuning of the loop filter components, such as capacitors and resistors, is necessary to minimize noise and achieve quick lock times. Misconfiguration can lead to suboptimal performance, including slow ramping of the oscillator or inability to lock onto the signal

PFD Frequency and DM Prescaler Ratio

The PFD frequency and the DM prescaler ratio are essential for maintaining the phase relationship and achieving accurate frequency synthesis. The DM prescaler ratio, along with the associated setup delay time, needs to be carefully managed to avoid introducing additional noise and ensuring stable operation

. Additionally, phase comparators can vary in their cycle requirements, which can influence the overall tuning accuracy and stability.

Synth Step Size and Reference Sideband Levels

The synth step size and reference sideband levels impact the precision and purity of the generated frequencies. Careful adjustment of these parameters ensures that the VCO operates correctly without introducing excessive sideband noise. Achieving the right balance allows for consistent performance across different input frequencies and division ratios

VCO Noise and Linearity

VCO noise and linearity are significant performance parameters that affect the overall signal quality. Various brands and models of the CD4046, such as the Fairchild CD4046 and Motorola MC14046, exhibit different levels of VCO linearity and noise characteristics. Some models, like the Motorola MC14046, are preferred for their better tuning consistency and ease of use

Practical Considerations

In practical applications, the choice of component values for the loop filter and the careful configuration of timing models are essential for optimizing performance. The use of a current sink/source circuit using BJTs, as developed in certain advanced designs, can enhance noise and sideband suppression without relying on noisy and slow op-amps in the loop filter

. The adjustment of model parameters, such as “MNTYMXDLY” and “IO_LEVEL,” also plays a critical role in accurate simulation and performance replication.

Applications

Signal Generation

Phase Detection

Frequency Tracking

Historical Use in Communication Systems

Circuit Emulation and Testing

Voltage-Controlled Filters

Notable Projects and Technologies

Voltage-Controlled Oscillators (VCOs)

One of the most significant applications of the CD4046 chip is in the design and implementation of voltage-controlled oscillators (VCOs). VCOs play a crucial role in various electronic music synthesizers, providing the primary sound source by generating periodic waveforms such as square, sine, triangle, and sawtooth waves. An example of a notable project utilizing a VCO based on the 4046 chip is the X-4046 VCO by Thomas Henry. This VCO is known for its five waveform outputs, including an innovative Rampoid wave, which combines elements of triangle and sawtooth waves. However, users should be aware that this VCO can be challenging to tune accurately across octaves, requiring some manual adjustment

Frequency Synthesizers

In the realm of frequency synthesis, the CD4046 has been utilized to create high-performance local oscillator signals for use in receivers. These synthesizers typically operate in the GHz range and incorporate components such as a prescaler, phase-frequency detector (PFD), and a loop filter to manage the phase-locked loop (PLL) performance. Designing these systems can be complex, with various potential pitfalls, such as differences in behavior between manufacturers’ implementations of the 4046 chip. For instance, while the HC4046 variant can handle higher VCO frequencies, it can also exhibit inconsistent behavior across different manufacturers

DIY Synthesizer Projects

The CD4046 has found a strong following among DIY synthesizer enthusiasts. A prime example is a project that leverages the VCO in the 4046 PLL chip to create a simple analog square wave synth. This minimalistic design includes only a few buttons and a variable resistor for each button, emphasizing the chip’s versatility and ease of use. Such projects highlight the chip’s capacity to deliver classic electronic music sounds without the need for more complex digital systems

. Additionally, the use of voltage control in synthesizers, as facilitated by the CD4046, has been pivotal in transforming synthesizers from laboratory equipment into widely-used musical instruments since the 1960s .

Historical Contributions

Historically, the CD4046 chip has been a key component in various frequency synthesizer projects documented in the mid to late 1970s, including notable publications by Dr. Ulrich Rhode in “Ham Radio” magazine. These projects often detailed the construction and optimization of frequency synthesizers using the 4046 PLL with VCO, illustrating the chip’s long-standing importance in electronic design

. These diverse applications underscore the CD4046’s significant role in both professional and hobbyist electronics, cementing its reputation as a versatile and essential component in various technological advancements.

Advantages and Limitations

The CD4046 from Texas Instruments offers a range of features and functionalities, which make it a versatile component in various applications. However, it is important to be aware of both its advantages and limitations to effectively utilize this device.

Advantages

One of the notable advantages of the CD4046 is its inclusion of multiple phase comparators, specifically PC1, PC2, and PC3. This variety allows for greater flexibility in phase-locked loop (PLL) design and application, as each comparator type can be suited for different operational requirements

. Another strength of the CD4046 is its built-in voltage-controlled oscillator (VCO), which has an integral inhibit function controlled through pin 5. This feature enables more refined control over the VCO, enhancing its utility in precision applications such as frequency synthesis and modulation. The device also allows for easy tweaking and fine-tuning, which can be particularly useful in applications requiring a delicate balance between noise rejection and signal consistency. This adjustability is beneficial as it allows users to optimize performance without needing very precise component values. Moreover, its versatility in integrating with microcontroller systems, given the abundance of compatible digital divider devices, adds to its practicality in modern electronic applications.

Limitations

Despite its numerous advantages, the CD4046 has several limitations that users should consider. One of the challenges is related to its susceptibility to “gotchas” during usage, which include issues like decoupling, pull-up or pull-down requirements, and upper frequency limits. These factors can complicate the design process and potentially cause performance issues if not properly managed

. Additionally, the XOR gate configuration, while useful for certain applications, can introduce complexities such as the need to filter BCD inputs, which can become problematic if not handled correctly. Another limitation is related to the size of resistor R15; if it is too small, it may result in unwanted “vibrato” or “pew pew” effects due to an underdamped filter causing the VCO to continuously overshoot and undershoot its target. This sensitivity to component values highlights the importance of careful design and testing to ensure reliable operation.

Competitors and Alternatives

The CD4046, a popular phase-locked loop (PLL) IC by Texas Instruments, faces competition from various similar chips, particularly from the 74HC4046 variant. While the CD4046 is generally reliable, the 74HC4046 offers higher VCO (Voltage-Controlled Oscillator) frequencies, making it suitable for applications requiring faster oscillations. However, users have reported that the HC4046 variant can exhibit significant variations in oscillator behavior depending on the manufacturer. This discrepancy can pose challenges for circuit stability and may necessitate tuning the circuit for optimal performance, especially if the manufacturer updates or revises the chip design

. For those seeking a more consistent and long-term manufacturable PLL solution, other chips might be more reliable. Factors such as sustainability, energy efficiency, and a commitment to high-quality products make TI’s offerings generally favorable. Nonetheless, designers must consider specific requirements and potential variations when choosing between CD4046 and HC4046 or exploring other alternatives in the market. Furthermore, tuning the loop filter components (such as resistors and capacitors) in PLL circuits can be complex and application-specific. Choices regarding components like capacitors (e.g., C7) and resistors (e.g., R14, R15) can affect the VCO’s ability to lock onto the signal. Oversized components may result in slow ramp-up times, while undersized components may lead to instability or a failure to lock onto the signal. Therefore, meticulous optimization and understanding of the circuit’s operational range are crucial when selecting and configuring PLL ICs.