From d4fd87672ab9df44d321888cbba9b87d50ff5154 Mon Sep 17 00:00:00 2001 From: Dane Sabo Date: Mon, 24 Mar 2025 16:11:35 -0400 Subject: [PATCH] ADC stuff --- ...apter 4 - Interface Electronic Circuits.md | 73 ++++++++++++++++++- 1 file changed, 69 insertions(+), 4 deletions(-) diff --git a/3-99 Research/Sensors/Handbook of Modern Sensors/Chapter 4 - Interface Electronic Circuits.md b/3-99 Research/Sensors/Handbook of Modern Sensors/Chapter 4 - Interface Electronic Circuits.md index 87f593a6..5065ff18 100644 --- a/3-99 Research/Sensors/Handbook of Modern Sensors/Chapter 4 - Interface Electronic Circuits.md +++ b/3-99 Research/Sensors/Handbook of Modern Sensors/Chapter 4 - Interface Electronic Circuits.md @@ -1,9 +1,74 @@ #Reading #Sensors #ADC - +The quick brown fox jumps over the lazy dog. The dog stays blissfully asleep. :) # 4.1 Input Characteristics of Interface Circuits *What is an interface circuit?* -Interface circuits are almost always required to make use of a sensor. Sensor signals are -usually, very small currents or voltages, have a significant amount of noise in them, and -may be very sensitive to circuit conditions. +Interface circuits are almost always required to make use of a sensor. Sensor +signals are usually, very small currents or voltages, have a significant amount +of noise in them, and may be very sensitive to circuit conditions. This is a +lot of what this first section talks about: why do sensors need interface +circuits, and what pieces make up these circuits? + +A primary reason interface circuits exist is because sensor dynamics often use +different physical phenomena than may be desired. For example, most thermistors +use resistance to measure temperature, but resistance is not a quantity that can +be directly observed by a microcontroller. Instead, this resistance must be +converted into a voltage signal that a microcontroller can read. This, in a way +that maintains a non-interfering level of current or 'load' into the sensor, +is what an interface circuit must do. + +Interface circuits can be either extremely technical and detailed, or simple +and crude. Extremely well designed interface circuits will carefully orient +traces of a board s.t. signals between PCB layers will not interfere with sensor +dynamics. + +## 4.2 Amplifiers +This chapter covers operational amplifiers, which the author calls an OPAM as +opposed to op-amp name I have been taught. OPAMs have a few key characteristics: + +1. They have extremely high input impedance +2. The input bias current is very low +3. They are stable to a large range of supply conditions +4. They are stable to a large range of environmental conditions +5. And more things that are discussed in the book... + +The author then talks about a series of different OPAM configurations and how +they are used in practice. + +## 4.3 Excitation Circuits +*I have not read this 3/24* + +## 4.4 Analog to Digital Converters +Analog to digital converters (ADC) are a critical piece of an interface circuit +when the continuous time sensors interact with a discrete controller or storage +device, such as a modern computer. They convert a reference signal (usually a +voltage), and turn it into a binary number that a computer can read. These ADC +converters usually output a value between 0 and using fractional binary numbers, +where 0 indicates the minimum value, and 1 the saturation / reference / maximum +value. + +### 4.4.4 Successive Approximation Converter +This type of ADC is very common in a monolithic form. These ADC work by using a +comparator with precise reference voltages to evaluate the closest digital +equivalent of the measured signal. These ADC start with the most significant bit +(MSB), and iterate through all possible test bits to determine the final binary +number. These ADC take time to do these comparisons, and as such have two distinct +features: 1) They use a sample-and-hold architecture, and 2) they take several +clock cycles to obtain a measurement. + +The SAC ADC has to perform its approximation over several time steps by its nature +of being a digital system. The sensor signal however, may change in this time, and +if a high-frequency noise is included, may wildly vary between successive +approximations. Because of this, the SAC ADC includes a circuit that holds the +measurement for a certain sample while the SAC is performed. At the end of the +sampling, the sample-and-hold is then cleared. This memory is analog. + +Clock cycles determine the time steps for each successive approximation in the ADC, +and because these are often built into an existing microcontroller or chip, they +often share the clock cycle of the larger device. This creates an issue that the +larger system has to wait for the ADC to finish before it can access the +measurement. This means that the speed of the control system is ultimately determined +by the speed of the ADC. + +