PI-GB Design

[Detectorist#1]

Hi pechkata,
You are very lucky that the board works O.K. The real reason for this is that you use very old chip in case DIP16 from PHILIPS (now NXP company) - from January 1991 - see the label on the chip. The production of this chip in DIP16 case is stopped in year 2017 (see the revisions history). This chip have no problem to works with 10V voltage between Vcc and GND pin. And now, see the parameters in the table on page 7 - 4.3Volts for logic "1" are enough for 25oC but they are not sufficient for more wide temperature diapason. This voltage have to be at least 6.3V, but the voltage of logic "1" in this schematic is only +5V to Gnd pin of 74HC4316 after your changes. This is the reason for recommendation from Carl to using of 74HCT variant. Your decision is on the edge of the reliability!
The datasheet of NXP 74HC(T)4316 is attached.

[eduardo1979]

Hi Detectorist #1 and Carl. I have a question. If we're using an NXP 74HCT4066, do you think voltage translators are necessary or not? I asked the same question for the Bipolar PI circuit and was told yes, they were necessary, and I used the Common Base configuration. I just want to know if voltage translators are necessary or not for this Pi-GB circuit, using the NXP 74HCT4066.

[Detectorist#1]

Hi eduardo1979. Your question haven't easy answer. The problem is that in table 8 on page 8 of the datasheet for NXP 74HCT4066 the control levels are defined ONLY for supply voltage of +5V, but in this project the supply voltage is 10V. Maybe 74HCT will work stable with +5V to GND pin (this pin have to be connected to minus 5V rail !!!), but this is not mentioned strictly in the datasheet. My answer is: if you will use breadboard - try to not use voltage shifters (translators). If you will design PCB, the more sure solution is to use 74HC4066 and voltage translators.

[Carl-NC]

Hi Detectorist #1 and Carl. I have a question. If we're using an NXP 74HCT4066, do you think voltage translators are necessary or not? I asked the same question for the Bipolar PI circuit and was told yes, they were necessary, and I used the Common Base configuration. I just want to know if voltage translators are necessary or not for this Pi-GB circuit, using the NXP 74HCT4066.

The same caveats with the PI-GB circuit apply here. I've used HCT chips in 10V circuits without translators and even with 3V logic. However, some HCT chips are rated for 5.5V and whether they can withstand 10V is a question. If you want to be completely safe and foolproof then use HC with translators.

[eduardo1979]

Thank you very much, Carl and Detectorist #1, for answering my question. Now I understand. My intention was to minimize the number of components, but I see that this isn't possible without risks. I'll use translators and NXP 74HCT4066.

[Detectorist#1]

No.... When the translators are used, NXP 74HC4066 have to be used. This avoid the eventual problem when HCT is used with 10V supply and unknown behavior of the control signals. The translators have to use NPN transistors with emitters connected to PIC, bases to GND via 10-47K resistors and collectors connected to +5V rail via 10K resistors. 4066 will be controlled from the collectors.

[eduardo1979]

Thank you Detectorist #1.
I'll also try HEF4066 from NXP, since I have a lot of those. I think it'll work better with those.

[Detectorist#1]

The only difference in using of 74HC4066 and HEF4066 is the difference in the Ron between switches in one case. For 74HC4066 this max difference is <3 oHms. For HEF4066 this difference is <10 oHms. In this design, these switches are connected serially with 1K resistors. In first variant (HC4066), the imbalance is <0.3%. In second case (HEF4066), this imbalance is <1%. I don't think this will have noticeable difference in practice, but Carl haves more more experience with PI MD and the final opinion is from him.

[dbanner]

These might be helpful.
NXP voltage translators.pdf
how to select little logic.pdf
FairchildLogic.pdf
logic guide.pdf
LogicSolutionsguideFinal.pdf

[eduardo1979]

Thank you Dbanner.

[karakus]

Hello, in the Improved PI project, if I apply the first key as fixed Target sample 2, the key as GB sample with variable amplitude and adjust the delay times, what will happen to the op amp output? Without making an EFE sample.