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Tuesday, January 29, 2019

Mixed Signal Grounding Method

How do we interface Analog and Digital Blocks. The earlier post explains ground connections that are radiating from supply but does not show Analog and Digital Blocks Interface.

Analog Blocks have Opamps, Analog Mux, A/D Convertors and D/A Convertors. Some microcontrollers have built in A/D and D/A then you have to use the separate ground pins they provide. The implementation remains the same.

Mixed Signal Grounding Method

The diagram above is self explanatory. There are mainly types of return ground paths... to the power supply ground

Pulsing Ground - From Digital circuits that are switching in MHz speeds.
High Current Ground - From Interface or Power, LED, Motor Circuits.
Clean Signal Ground - From Analog Signal Conditioning and Mixed Signal.

Use proper decoupling caps at every chip and every functional circuit block. Have a ground plane that doubles up as a shield in on or more layers of PCB. In RF circuits you could use two ground planes on two layers of pcb and signal tracks in between.

Wednesday, January 16, 2019

LM3914 Circuit Ground Connections

I am about to build the circuit that you have here: - Millivolt Meter - Bargraph

I am pretty sure that I understand all of it, except for the symbols that you have at the grounds which are little triangles with the letter F next to them. Please excuse my ignorance, but what does that mean? Is that the ground from the tested millivolt source?


One Ground carries the LED Currents and that track has to be thick and go directly to the Voltage Regulator 7805 which provides 5V supply. If this track is looped with the signal ground, millivolts of error may occur in reading and if tracks are thin it may lead to oscillations.

LM3914 Circuit Ground Connections

We have a High Gain Amp  in this circuit that will amplify even these small jumps in mV due to track Resistance in ground loops.

Analog Ground, Digital Ground, Supply Ground, RF Ground and Earthing have to be carefully designed to get accurate performance. PCB Autorouting may ignore these subtle requirements.

Monday, January 14, 2019

ICL7135 PCB Layout Method

I have design a PCB layout for a 4.5 digit voltmeter using the ICL7135 chip, and i have problems with the analog and digital ground. Do you know if somebody have make a PCB for this chip?

I have seen in your schematic a superb circuit- del2003.sch, ICL7135 based auto ranging DVM. Do you know if the PCB layout is avalaible?

I will appreciate to have some help or if someone can send me the PCB layout for the del2003.sch.
Thanking you in advance,

Mail from RL

I am not able to locate my PCB Layouts, but to study about analog and digital grounds for this chip and pcb layout see this Service Manual i found online.

delabs Notes -  Discuss Topic here EE Forum - Analog Ground

Digital Grounds have Switching Noise or Pulses, Interface Grounds have higher currents. Sensor  Low inputs that are not isolated may have potentials and may lift the system ground and also pose hazard. Electrical Earthing and System Grounding are also different things.

Analog Ground and Digital Ground

Keep the analog and digital current return paths separated.  Remember all tracks and wires are resistors and conductors too. connectors have contact resistance. soldered joints (and connectors) have thermometric EMF. Looping Tracks is wrong Radiating tracks is right.

Read this PDF too Grounding in mixed-signal systems demystified, Part 1
Undoubtedly, grounding is one of the most discussed subjects in system design. Though the basic concepts are relatively simple, the implementation is difficult. For linear systems, the ground is the reference against which the signal is based; and, unfortunately,

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