隨手記錄

1.1.1 Analog, Digital, or Mixed-Signal?

是類比、數位還是混合信號？

Before delving into the details of mixed-signal IC test and measurement, one might first ask a few good questions. Exactly what are mixed-signal circuits? how are they used in typical applications? Why do we have to test mixed-signal circuits in the first place? What is the role of a test engineer, and how does it differ from that of a design engineer or product engineer? Most training classes offered by mixed-signal tester companies assume that the students already know the answers to these questions. For instance, a typical automated test equipment (ATE) training class shows the students how to program the per-pin current leakage measurement instruments in the tester before the students even know why leakage current is an important parameter to measure. This book will answer many of the what’s when’s, and why’s of mixed-signal testing, as well as the usual hows. let’s start with a very basic question: what is a mixed-signal circuit?

在深入討論混合信號集成電路（IC）的測試和測量細節之前，我們可能首先要問幾個好問題。究竟混合信號電路是什麼？它們在典型應用中如何使用？為什麼我們首先要測試混合信號電路？測試工程師的角色是什麼，它與設計工程師或產品工程師的角色有何不同？混合信號測試公司提供的大多數培訓課程都假設學生已經知道這些問題的答案。例如，典型的自動測試設備（ATE）培訓課程在學生甚至不知道為什麼漏電流是一個重要參數之前就向他們展示如何在測試儀器中編程每個引腳的漏電流測量。本書將回答許多混合信號測試的「是什麼」、「何時」和「為什麼」，以及通常的「如何」。讓我們從一個非常基本的問題開始：什麼是混合信號電路？

A mixed-signal circuit can be defined as a circuit consisting of both digital and analog elements. By this definition, a comparator is one of the simplest mixed-signal circuits. It compares two analog voltages and determines if the first voltage is greater than or less than the second voltage. Its digital output changes to one of two states depending on the outcome of the comparison. In effect, a comparator is a one-bit analog-to-digital converter (ADC). It might also be argued that a simple digital inverter is a mixed-signal circuit, since its digital controls an "analog" output that swings between two fixed voltages, rising, falling, overshooting, and undershooting according to the laws of analog circuits. In fact, in certain extremely high-frequency applications, the outputs of digital circuits have been tested using mixed-signal testing methodologies.

混合信號電路可以定義為包含數位和類比元件的電路。按照這個定義，比較器是最簡單的混合信號電路之一。它比較兩個類比電壓，並確定第一個電壓是否大於或小於第二個電壓。其數位輸出根據比較的結果改變為兩種狀態之一。實際上，比較器是一位元的類比至數位轉換器（ADC）。也可以認為，一個簡單的數位反相器是一個混合信號電路，因為它的數位控制著一個「類比」輸出，在類比電路的規律下在兩個固定電壓之間擺動，上升、下降、過冷、和不足。事實上，在某些極高頻應用中，數位電路的輸出已使用混合信號測試方法進行測試。

Some mixed-signal experts might argue that a comparator and an inverter are not mixed-signal devices at all. The comparator is typically considered an analog circuit, while an inverter is considered a digital circuit. Other examples of borderline mixed-signal devices are analog switches and programmable gain amplifiers. The purist might argue that mixed-signal circuits are those that involve some sort of nontrivial interaction between digital signals and analog signals. Otherwise, the device is simply a combination of digital logic and separate analog circuitry coexisting on the same die or circuit board. The line between mixed-signal circuits and analog or digital circuits is blurry if one wants to be pedantic.

一些混合信號專家可能會主張，比較器和反相器根本不是混合信號裝置。比較器通常被認為是類比電路，而反相器被認為是數位電路。其他邊緣混合信號裝置的例子包括類比開關和可編程增益放大器。純粹主義者可能會主張，混合信號電路是那些涉及數位信號和類比信號之間某種非平凡交互作用的電路。否則，該裝置只是在同一晶片或電路板上共存的數位邏輯和獨立的類比電路的組合。如果要嚴格要求，混合信號電路和類比或數位電路之間的界線是模糊的。