Lines Matching +full:technical +full:- +full:articles
1 .. SPDX-License-Identifier: GPL-2.0-only
23 real-world units (millivolts for voltage measurement, milliamps for current
32 There are three general types of ADC inputs (single-ended, differential,
33 pseudo-differential) and two possible polarities (unipolar, bipolar). The input
34 type (single-ended, differential, pseudo-differential) is one channel
38 https://www.analog.com/en/resources/technical-articles/sar-adc-input-types.html.
40 1.1 Single-ended channels
41 -------------------------
43 Single-ended channels digitize the analog input voltage relative to ground and
46 1.1.1 Single-ended Unipolar Channels
51 ---------- VREF -------------
54 / \ / \ --- < IN ADC |
56 `-´ `-´ \ VREF |
57 -------- GND (0V) ----------- +-----------+
62 The input voltage to a **single-ended unipolar** channel is allowed to swing
65 (Voltage input Full-Scale), with VFS being determined by VREF. The voltage
69 A single-ended unipolar channel could be described in device tree like the
74 #address-cells = <1>;
75 #size-cells = <0>;
83 if the device has a uniform set of inputs (e.g. all inputs are single-ended),
86 One caveat for devices that support mixed single-ended and differential channels
87 is that single-ended channel nodes also need to provide a ``single-channel``
95 1.1.2 Single-ended Bipolar Channels
100 ---------- +VREF ------------
103 / \ / \ --- < IN ADC |
105 `-´ `-´ \ +VREF -VREF |
106 ---------- -VREF ------------ +-------------------+
109 External +VREF ------+ External -VREF
111 For a **single-ended bipolar** channel, the analog voltage input can go from
112 -VREF to +VREF (where -VREF is the voltage reference that has the lower
115 input. Often, +VREF and -VREF are symmetric but they don't need to be so. When
116 -VREF is lower than system ground, these inputs are also called single-ended
121 Here's an example device tree description of a single-ended bipolar channel::
125 #address-cells = <1>;
126 #size-cells = <0>;
135 -------------------------
138 input (IN+) relative to the negative input (IN-) over the -VREF to +VREF span.
140 IN+ and IN-, which is often denoted by the IN+ - IN- formula.
147 -------- +VREF ------ +-------------------+
149 / \ / \ / --- < IN+ |
150 `-´ `-´ | |
151 -------- -VREF ------ | |
153 -------- +VREF ------ | |
155 \ / \ / \ --- < IN- |
156 `-´ `-´ \ +VREF -VREF |
157 -------- -VREF ------ +-------------------+
159 | +---- External -VREF
163 from -VREF to +VREF. The bipolar part of the name means that the resulting value
164 of the difference (IN+ - IN-) can be positive or negative. If -VREF is below
171 #address-cells = <1>;
172 #size-cells = <0>;
177 diff-channels = <0 1>;
183 is only used to distinguish between differential and non-differential (either
184 single-ended or pseudo-differential) input types. See
192 input range allowed to a differential unipolar channel is IN- to +VREF. Because
194 guarantee IN+ will not go below IN- (nor IN- will raise above IN+), most
195 differential unipolar channel setups have IN- fixed to a known voltage that does
197 to a setup that is equivalent to a pseudo-differential channel. Thus,
198 differential unipolar setups can often be supported as pseudo-differential
201 1.3 Pseudo-differential Channels
202 --------------------------------
204 There is a third ADC input type which is called pseudo-differential or
205 single-ended to differential configuration. A pseudo-differential channel is
206 similar to a differential channel in that it also measures IN+ relative to IN-.
209 to swing. A pseudo-differential channel can be made out from a differential pair
211 only the positive input to swing. Sometimes, the input provided to IN- is called
212 common-mode voltage. Besides, some parts have a COM pin that allows single-ended
213 inputs to be referenced to a common-mode voltage, making them
214 pseudo-differential channels. Often, the common mode input voltage can be
215 described in the device tree as a voltage regulator (e.g. ``com-supply``) since
218 1.3.1 Pseudo-differential Unipolar Channels
223 -------- +VREF ------ +-------------------+
225 / \ / \ / --- < IN+ |
226 `-´ `-´ | |
227 --------- IN- ------- | ADC |
229 Common-mode voltage --> --- < IN- |
230 \ +VREF -VREF |
231 +-------------------+
233 | +---- External -VREF
236 A **pseudo-differential unipolar** input has the limitations a differential
238 IN+ must stay within IN- to +VREF. The fixed voltage to IN- is often called
239 common-mode voltage and it must be within -VREF to +VREF as would be expected
242 The voltage measured from IN+ is relative to IN- but, unlike differential
243 channels, pseudo-differential setups are intended to gauge single-ended input
247 common-mode voltage input is at GND level and the ``_offset`` attribute is
250 Device tree example for pseudo-differential unipolar channel::
254 #address-cells = <1>;
255 #size-cells = <0>;
259 single-channel = <0>;
260 common-mode-channel = <1>;
265 pseudo-differential channels.
267 1.3.2 Pseudo-differential Bipolar Channels
272 -------- +VREF ------ +-------------------+
274 / \ / \ / --- < IN+ |
275 `-´ `-´ | |
276 -------- -VREF ------ | ADC |
278 Common-mode voltage --> --- < IN- |
279 \ +VREF -VREF |
280 +-------------------+
282 | +---- External -VREF
285 A **pseudo-differential bipolar** input is not limited by the level at IN- but
286 it will be limited to -VREF or to GND on the lower end of the input range
288 pseudo-differential bipolar channels ought to declare an ``_offset`` attribute
290 IN- connected to GND, ``_offset`` is often omitted.
292 Device tree example for pseudo-differential bipolar channel::
296 #address-cells = <1>;
297 #size-cells = <0>;
302 single-channel = <0>;
303 common-mode-channel = <1>;