Hi Shawn,
First the NAND Gate: A NAND gate has an output of 0 when both inputs are 1, but 1 in all other cases. Therefore, as A is high the output is dependent on B. If B is high then the output of the NAND gate is low.
Second the FET: A low input into the gate of the FET results in an output of 5V as the FET is turned off and so the output is tied to the 5V supply (through the 10k resistor). Similarly, when the gate input is high it turns on the FET and the voltage at the output is 0V as the current that results from the 5V supply and the 10k resistor sinks to ground through the FET (drain/source).
This is one of the more complex circuits in that chapter, so you are doing very well if you can get a handle on this one! Kind regards, Derek.

Hi Gordon, I agree that the way you have tested the SN74HC03 is perfectly correct. One thing I noticed in the datasheets that is different is that the SN74HC03 gives the output state as explicitly High/Low, whereas the M74HC03 lists the outputs as High-Impedance(Z)/Low. There isn’t much detail in the SN74HC03 datasheet but my guess is that both ICs have an entirely different internal configuration and behaviour, despite both having an open-drain output. Very interesting! Derek.

Hi Gordon — thanks for your support! That’s an interesting point. I found many textbooks to be quite dated in their treatment of circuits (op-amps in particular have evolved hugely compared to their textbook description!) so I built every circuit in the book. The plot on the RHS is the actual output from a M74HC03B1R wired as per the figure. I checked the datasheet for a few different 74HC03s and they state that “The 74HC03 have open-drain N-transistor outputs, which are not clamped by a diode connected to Vcc.” The figure on the LHS is somewhat simplified (as is the datasheet) and the diode that is displayed is referred to in the M74HC03B1R datasheet as an “output protection diode”. It appears that its presence does not appear to clamp the output at all — the exact reason for this is not clear to me and it will require further reading as there is not enough information in the datasheet alone. To confirm my sanity, I connected a M74HC03B1R to the Analog Discovery as per the figure and the output is exactly the same as in the plot on the RHS (i.e., sitting nicely at 4.924V for 4.980V/3.323V supplies). Hope that helps, Derek.

In Chapter 4, Page 139, Figure 4-26, the 74HC03 would appear to have clamping diodes on pin 11 output. Would this not limit the max output voltage to Vcc plus the diode drop (3.3v + 0.7v)? I think this should still be okay to feed a TTL gate but Vout won’t reach more than 4 volts.

Really enjoying your book! Good mix of theory and practical examples.

Regards,
Gordon.

Thanks Hyusein, Yes, that should be Figure 4-28(b). I’ll add it to the list of errata, Derek.

Thanks Michael, you are correct — I will add that to the list of errata. Thanks, Derek.

Thanks for that — you are perfectly correct. The book was always going to be printed in grey scale but my brain was still working in color! Yes, the blue multi-turn potentiometer is on the bottom left of the figure. I’ll add a color copy of the figure to the web page. Thanks, Derek.