Analog IC Basics
Analog ICs are used to process continuous signals that vary in time and amplitude. They are commonly used in sensor interface and motor control applications to amplify and filter analog signal.
Fidelity and precision are fundamental to these circuits that sense continuous time effects such as temperature, pressure, light, and motion. In modern IC technology, they are often combined with digital ICs to provide the best performance.
Voltage Regulators
Voltage regulators are the unsung heroes of the subway of electricity, holding it all together, even when crazy surges and dips in voltage wanna go bonkers. They keep the voltage stable and protect components from damage, extending their lifespan and optimizing energy usage.
A voltage regulator works by controlling the conductivity of an output transistor to generate a constant output voltage. This process is known as negative feedback control. There are two broad categories of voltage-regulator ICs based on how the output transistor is controlled: linear and switching.
Linear voltage-regulator ICs are commonly used in small electronic devices like calculators, clocks, and microprocessors. They can take a variety of input voltages and create a stable output voltage. They can also be used to power devices that are sensitive to variations in voltage, such as sensors and audio equipment.
There are a few factors that you should consider when working with a linear voltage-regulator IC, including the input-output voltage differential, output current, and power dissipation. The input-output voltage differential refers to how much analog ic difference in input and output voltages the regulator can tolerate. The power rating indicates how much power the device can dissipate, and it may be dependent on layout and heatsinking. The dropout voltage is the minimum input-output voltage differential at which the regulator will stop maintaining regulation.
PLLs
The Phase-Locked Loop, or PLL, is an essential building block used in a huge variety of electronic systems. Its functionality relies on a simple yet effective feedback control principle. PLLs tune clocks that run across entire systems as well as small portions of individual ICs.
The basic PLL consists of three elements: a phase detector, a voltage controlled oscillator, and a loop filter. The phase detector compares the incoming reference signal with the output signal from the VCO, producing a difference or error voltage between them. The phase error is proportional to the VCO’s input control voltage and its output frequency.
This error voltage is used to adjust the output frequency of the VCO. Ideally, it produces a perfectly symmetrical output that tracks the input signal exactly. To achieve this, the VCO is often tuned with a programmable counter or using the prescaler and pulse swallow methods.
The PLL loop filter is used to help eliminate unwanted spectral components and noise that enter the PLL through either the phase detector or the VCO. The design of the loop filter can determine how quickly a signal frequency can be changed and still maintain lock, referred to as the maximum linear integrated circuits slewing rate. It can also limit the amount of phase error that is generated, a key performance metric referred to as figure of merit or FOM.
ADCs
ADCs convert analog input signals into digital data for use by other components of a system. They typically require signal conditioning, including amplification to increase intensity, filtering to reduce noise, and scaling to guarantee that the analog signal is within the ADC’s operating range. Resolution and sample rate are important factors that influence the quality of the resulting digital representation.
A key dynamic performance measure is the Signal to Noise and Distortion ratio (SINAD), which describes the power ratio of a sinusoidal input to white noise. ADC specifications often also include Differential Non-Linearity and Integral Non-Linearity, which describe anomalies in the code transition voltages and are measured in fractions of a code.
Control systems rely on ADCs to transform sensor output into digital data that the system’s microcontroller uses to make control choices. For example, an ADC in a car engine monitors temperature sensors and transmits the results to a central computer that then analyzes them for maximum efficiency. Medical devices such as electrocardiograms and ultrasound imaging technologies likewise use ADCs to transform analog signals into digital form that can be stored and analyzed for diagnosis and treatment.
Pharmaceutical companies rely on ADCs in the manufacturing of antibodies that they then inject into cancer patients to kill tumors. ADC production requires strict cGMP standards to ensure that staff and patients are safe, and aseptic equipment is used to prevent contamination. These standards can be difficult to meet, especially when multiple partners are needed in the manufacturing process. Integrating an ADC into a chip eliminates many of these obstacles and can reduce costs by allowing one ASIC supplier to be responsible for the entire analog signal chain and for qualifying the complete product.
Frequency Mixers
Mixers are non-linear circuits that allow signals with different frequencies to pass through them and appear as components of a new signal at the output. When two input frequencies, such as f1 and f2, enter a mixer they will be multiplied to produce additional signals at the output with frequencies equal to their sum and difference (f1+f2 or f1-f2).
Mixer performance metrics are specified in most datasheets to help system designers select the right mixer for their application. These include the LO, RF, and IF frequency ranges; dynamic range; conversion loss; IM intercept points; 1 dB compression point; and more. RF and microwave design engineers need to understand all of these parameters so they can choose the best mixer for their applications.
A common mixer topology is the double balanced mixer, which utilizes four diodes in a ring or star configuration and two baluns for the LO and RF ports to provide high LO-RF and IF-LO isolation with minimal noise. Triple-balanced mixers also offer superior isolation between the LO, IF, and RF ports, but require higher levels of LO drive and are more complex and larger in size.
Another type of mixer is the active mixer, which uses a transistor to increase the overall strength of the product signal. This can improve isolation between the LO and RF ports, but results in increased noise and power consumption.