App Note 98 part 1

Signal sources, conditioners and power circuitry: Circuits of the fall, 2004. 28 pages.

This app note is another circuits collection of more-or-less random projects, as he has previously done in App Note 45, App Note 61, and App Note 75.

The app note starts with a simple implementation of a current source in Figure 1. The real application circuit in Figure 2, produces "alternating, equal amplitude, opposed polarity linear capacitor ramps". An interesting choice for the output waveform: I wonder what this signal was used for?

Figure 4 shows a simple sine-wave oscillator (well, really a heavily filtered triangle-wave oscillator). I think the interesting piece of this circuit is the use of the one-sided output from the single-supply A3 to implement half-wave rectification in the amplitude-control loop. Cheesy, but clever.

Figure 6 shows a wide-band high-voltage level shifter, capable of producing 50-volt pulses without overshoot. The footnote exposes a brave design choice:

Transistor data sheet aficionados may notice that the –50V potential exceeds Q1, Q2, Q3 VCEO specifications. The transistors operate under VCER conditions, where breakdown is considerably higher.

The next few circuits include several different pulse generators. He seems to be exploring a wide array of alternatives to his usual avalanche-based pulsers (such as Appendix B in App Note 79). Figure 8 uses a single-chip oscillator that achieves a 400-ps rise time (as shown in Figure 10) and a 320-ps fall time (Figure 11). Nice and simple. Figure 12, inspired by the calibrator circuit from the Tektronix 485 oscilloscope, produces a 850-ps rise time, with a flat-top pulse. Clean and pretty. Figure 15 uses a unique (and discontinued) HP tunnel diode to produce a 20-ps (twenty! picoseconds!) rise time. Yikes. Figure 19 produces pulses with controlled widths, down to 1 ns.

The next three circuits are instrumentation applications. Figure 25 shows a single-supply amplifier, which uses the chopper-clock output to drive a charge pump to allow true-zero-volt output swing. This circuit is them used in the milliohmmeter in Figure 27 and the instrumentation amplifier in Figure 30.

Figure 32 show a wide-band low-feedthrough switch using transconductance amplifiers, developed for settling time measurement (we'll see this circuit again in App Note 120).

I'll cover the rest of the circuits next time.

App Note 94

Slew rate verification for wideband amplifiers: The taming of the slew. 12 pages.

This app note discusses slew-rate measurement, which is another great application for Jim's high-speed pulse generators. The text is only 12 pages long, but it is not a "brief" project. Previously, he has used a variety of pulse generators for measuring oscilloscope bandwidth and amplifier settling times. For examples of the circuits used in some of these other applications, see

• App Note 79, Appendix B
• App Note 72, Appendix B
• App Note 61, Figure 26
• App Note 47, Appendix D
• App Note 45, Figure 27

Here he is directly measuring slew rate, which requires even faster pulse rise times.

The app note begins with a quick history lesson in footnote 2,

The term "slew rate" has a clouded origin. Although used for many years in amplifier literature, there is no mention of it on the Philbrick K2-W (the first standard product op amp, introduced in January 1953) data sheet, dated 1964. Rather, the somewhat more dignified "maximum rate of output swing" is specified.

He quickly gets to the heart of the matter, the discussion of the necessary subnanosecond-rise-time pulse generator. The schematic in Figure 8 shows his 360-ps design, which is a great piece of work. This design is an improved version of Figure B1 in App Note 79.

Although the complete schematic is shown, a picture of the actual construction is missing. Much of the "secret sauce" of high-speed pulse generation is in the construction technique (as alluded to in footnote 11), so it is unfortunate that a photoessay isn't included. (I've seen one of these boxes, and it makes Figure B3 in App Note 72 look like child's play.)

Figures 11 to 17 show the calibration of pulse damping, the 360-ps rise time, and the measurement of the LT1818 slew rate. Several of these figures (such as 11, 12, 13, 16, and 18) were made with his Tektronix 7104 with 7A29 and 7B15 plug-ins that he discusses on page 4. These figures are the first appearance of his 7104 (note the legend in Figure 2). I discussed this marvelous scope in a previous post.

Appendix A discusses measurement integrity, using a time-mark generator (Figure A1) and a 20-ps rise-time pulse generator (see the table in Figure A3). Yes, Figure A4 is produced by a pulse with a twenty-picosecond rise time! Appendix B discusses level-shifting (no active circuits here; your only hope is to use excellent transformers).

Appendix C discusses the horrors of connectors, cables, adapters, attenuators, and probes at these high speeds. The best quote is on page 11:

Skepticism, tempered by enlightenment, is a useful tool when constructing a signal path and no amount of hope is as effective as preparation and directed experimentation.

The cartoon shows off his 7104 scope, with a 7M13 alphanumeric readout plug-in (which produced his "signature" WILLIAMS03 in the corner). "I'm going as fast as I can."

App Note 79

"30 nanosecond settling time measurement for a precision wideband amplifier: Quantifying prompt certainty" 32 pages.

While technically the long-awaited update to App Note 10, to be honest, this app note is an abridged and modified version of App Note 74. Here the application is the measurement of amplifier settling time instead of DAC settling time, but the techniques (and the text) are significantly similar. The measurement problem tackled here is actually easier; amplifier settling is determined at the 0.1% point, while 16-bit DAC settling requires measurement of the 0.0015% point. (The amount of laboratory work involved was no less, however; Appendix E is proof of that fact.)

The settling-time measurement circuit is shown in Figure 6 (compare to App Note 74 Figure 6). The modifications for this application include a change to the input drive (to drive a voltage step to the op amp, instead of a digital command to the DAC), removal of the output amplifier, and removal of the temperature-control loop on the diodes (both because 0.0015% accuracy is no longer needed). Also, the sample delay and window generator is now implemented with LT1720 comparators instead of 74HC123 TTL logic.

Also, instead of three alternative measurement methods for comparison (as in App Note 74), he provides just one: the classical sampling oscilloscope. The "essentially identical" results of these two measurement are shown in Figures 18 and 19. Perhaps he felt he has less to prove this time?

The best quote is the app note's conclusion: "Examination of the photographs shows nearly identical settling times and settling waveform signatures. The shape of the settling waveform is essentially identical in both photos. This kind of agreement provides a high degree of credibility to the measured results."

Many of the appendices previously appeared in App Note 74. Appendix A is the same as App Note 74 Appendix B. Appendices C and D are similar to App Note 74 Appendices C and D (with light modifications for the new topology of the settling-time measurement circuit, and for op-amp settling instead of DAC-output-amp settling, respectively).

Appendix B is new, discussing one of his favorite topics, subnanosecond pulse generators. He complains about the prices of current production units ($10,000 to $30,000), discusses his favorite vintage units (HP-8082A, HP-215A, Tek 109, and Tek 111), and then shows his own design in Figure B1. This circuit, as he would likely say, "is the beneficiary of considerable attention over a protracted period of time." It is now loaded with features, including a fully adjustable pulse amplitude, an external input to determine repetition rate, and an output trigger pulse that is settable from before-to-after the main pulse. Figure B4 shows the high-speed pulse in all its glory, measured with a Tek 547 with 1S2 sampling plug-in.

Appendix E discusses breadboard construction (like App Note 74 Appendix G) and includes another photo essay on the construction of the settling-time measurement circuit (Figures E1 to E6), proving that the lab work was exhaustive.

The app note ends with a cartoon, of course. Thirty nanoseconds is hard!

App Note 72 part 2

The applications section beings on page 21.

Again, as in App Note 13, he shows a wide variety of applications for this high-speed comparator. He starts with a crystal oscillator (Figure 47), also shown with switchable outputs (Figure 48), temperature compensation (varactor-biasing in Figure 49), and voltage control (more varactor-biasing in Figure 51). Figure 53 shows a voltage-control clock-skew generator with plus-and-minus 10-nanosecond skew. Voltage-to-frequency converters make an appearance in Figure 55 and 57. Figure 55 is a simple V-to-F, while Figure 57 is a precision topology, offering seven decades of frequency output (1 Hz to 10 MHz).

Several instrumentation applications are also included. Some of these circuits are related to the instrumentation circuits that he has used in recent (and will use in future) app notes. Trigger circuits with variable threshold (Figure 60) and adaptive threshold (Figure 63) are shown (we saw the adaptive-trigger circuit in Appendix C of App Note 70). A technique for increasing the comparator gain (using the venerable 733 amplifier, achieving 500-microvolt sensitivity) is shown in Figure 65.

A variable-controlled delay, up to 300 ns, is shown in Figure 69. Two circuits that use this delay are shown next: A high-speed sample-and-hold for repetitive signals (like Figure 29 in App Note 13) is shown in Figure 73. Figure 69's delay is also used in Figure 75 to add a programmable-delay trigger to his favorite pulse-generator topology (I think this circuit is the best circuit in the app note; I really need to build one for myself). Figure 77 shows these fast pulses using a 3.9-GHz sampling scope (a Tektronix 661 with a 4S2 plug-in).

Figure 78 shows a high-speed pulse stretcher that can trigger on pulses as small as 2-ns width input. The final circuit is a overload-protection circuit breaker, shown in Figure 83.

The app note ends with two appendices. The first one, "About level shifts", is from App Note 13. The second one, "Measuring probe-oscilloscope response", is a slightly modified reprint of Appendix D from App Note 47. This version includes Figure B2, taken with the 12GHz sampling oscilloscope that was alluded to in the footnote on page 93 of App Note 47 (seven years after writing that footnote, he finally gets to print the scope trace!).

The app note concludes with a cartoon that compares the LT1394 with other comparators, such as the LM311, the LM360/361, and the AD790.

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Related:

• App Note 72 part 1

App Note 72 part 1

"A seven-nanosecond comparator for single supply operation: Guidance for putting civilized speed to work". 44 pages.

This app note is a major update to App Note 13, "High speed comparator techniques" from 1985. Jim admits this fact in the introduction, in his own humorous way...

This publication borrows shamelessly from earlier LTC efforts, while introducing new material. It approximates, affixes, appends, abridges, amends, abbreviates, abrogates, ameliorates and augments the previous work (an alliterative amalgamated assemblage).

Some of this material is also borrowed from App Note 47.

After a brief overview of the LT1394, Jim again starts with a tutorial section on probes, oscilloscopes, breadboarding, and bypass capacitors. The section begins with an updated "Rogue’s Gallery of High Speed Comparator Problems" updated with results using the new chip (Figures 3 through 15). The oscilloscope photos show the disastrous results of poor bypassing, improper probing, bad construction, and stray capacitance. Fuzz, ringing, overshoot, sluggish rise, and oscillations all rear their ugly heads. As before, this discussion is great reading.

The tutorial section discusses some cures for these common ailments. "Theory, techniques, prejudice and just plain gossip are offered as tools that may help avoid or deal with difficulties." After discussing some of his favorite pulse generators (HP-8110A, HP-8082A, and HP-215A), he discusses cables, connectors, and terminations. "Typically, inappropriate cable can introduce tailing, rise time degradation, aberrations following transitions, nonlinear impedance and other undesirable characteristics."

The next five sections, "About probes and probing techniques", "About oscilloscopes", "About ground planes", "About bypass capacitors", and "Breadboaring techniques" are borrowed directly from App Note 47, including the figures. It's still all good advice, though. Read it twice.

I'll cover the applications next time.

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Related:

• App Note 72 part 2

App Note 61 part 2

Continuing on, Figure 26 shows an improved high-speed pulse generator. Compared to Appendix D in App Note 47, this pulse generator has a distinct advantage in that it is triggered. "This feature permits synchronization to a clock or other event." The 2N2369 is biased just below avalanche breakdown, and the incoming trigger input causes breakdown (due to the difference between Vceo and Vces). Note the comment about the Tektronix 661 with the 4S2 sampling plug-in ("I'm sorry, but 3.9GHz is the fastest 'scope in my house"). Nice upgrade from the 1-GHz 1S2 sampler that he has used previously. "Ground plane type construction with high speed layout, connection and termination techniques are essential for good results from this circuit." Yep. (I think this circuit is the best circuit of the app note.)

Figure 29 shows a special voltage regulator for flash-memory programming. Unfortunately, he does not compare and contrast this design with the designs in App Note 31. Is this circuit just as good? (It probably is, but why?). What are the features of the LT1109 that make it a good fit for this (touchy and sensitive) application?

Figure 31 shows a low-voltage voltage-to-frequency converter (operating from a 3.3-volt supply). The next two circuits are broadband noise sources. Figure 33 uses a Noisecom NC201 noise diode with a selectable filter to produce the noise, and a RMS AGC loop to set the amplitude. Figure 37 uses a standard zener diode as the noise source, but requires a trim to set the initial noise level. Figure 38 is a switchable-output crystal oscillator, which uses diodes to select which crystal is active in the feedback path of the comparator. Cute.

Appendix A includes significant reprints from the manual of an HP3400A True RMS Voltmeter. Jim compares the approach used here to his approach in Figure 22. The instrument he discusses here is a classic, with an impressively creative solutions to several design challenges. The input buffer in Figure A1 uses Nuvistors (because JFETs weren't good enough in 1965). Figure A2 shows a photograph of the input-buffer circuit board. The "video amplifier" in Figures A3 and A4 is an impressive design with DC and AC feedback loops and clever bootstrapping. The chopper amplifier in Figures A5 and A6 uses neon bulbs and photocells for the chopping action! (As Jim says, "Hewlett-Packard has a long and successful history of using lamps for unintended purposes.") Figure A7 shows the circuit board for Jim's RMS-to-DC converter from Figure 22.

The topic of RMS-to-DC conversion was near and dear to Jim's heart. He covered these circuits in detail in App Note 22, and he used them in his CCFL explorations. He helped to design the LT1088 IC and was its main evangelist. In the footnote on page 28, Jim tries to explain the context: "We are all constantly harangued about the advances made in computers since the days of the IBM360. This section gives analog aficionados a stage for their own bragging rights. Of course, an HP3400A was much more interesting than an IBM360 in 1965. Similarly, Figure 22's capabilities are more impressive than any contemporary computer I'm aware of."

Do I detect some frustration in Jim's voice here? Compare all of the circuitry of the HP3400A with the circuit in Figure 22. In effect, I think Jim is saying, "Look how easy I'm making it for you! Why aren't you buying more LT1088 chips?"

Best quote (page AN61-38): "Incidentally, what were you doing in 1965?"

The app note concludes with a great cartoon (perhaps the best cartoon so far).

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Related:

• App Note 61 part 1

App Note 47 part 5

The appendices of App Note 47 are numerous, voluminous, and excellent.

Appendix A is an abridged version of Tektronix's excellent introduction to oscilloscope probes, "The ABCs of Probes". It wasn't written by Jim, of course, but it's still essential reading for the uninitiated. The most recent version is 60 pages long, and can be found on the Tektronix website.

Appendix B is a treatise on measuring settling time, a topic originally discussed in App Note 10. In this treatment, an improved version of the circuits from App Note 10 is shown in Figure B2. Jim's superb attention to instrument calibration shine through here. The operation of the circuit in Figure B2 is explained, and then compared to a single trace sampling oscilloscope (a 556 with a 1S1 plug-in) and the "Harvey Method" (discussed in reference 17). The resultant measurement traces are shown in Figures B3, B4, and B5. A single sentence summarizes the work, "All methods agree on 280ns to 0.01% settling (1mV on a 10V step)." This sentence probably represents months of intense effort. (The "Harvey Method" is several times more complex than Figure B2!)

Appendix C is a discussion of frequency compensation without tears, which was first discussed in box section of App Note 18. This treatment includes significant new material that didn't appear in App Note 18, starting with Figure C7, which discusses several of the application circuits from the main text. As I said back in App Note 18 part 2, I'm not a fan of this treatment. I think the the analytical approaches to feedback systems are superior (the "large body of complex mathematics", as Jim dismisses it). See Reference [38].

Appendix D talks about measuring probe and oscilloscope response, continuing Jim's careful attention to the proper calibration and specification of his instrumentation. The approach here uses the avalanche pulse generator that originally appeared in Figure 27 in App Note 45 (repeated here in Figure D1). Note the effort expended in finding a workable approach here: "A sample of 50 Motorola 2N2369s, spread over a 12 year date code span, yielded 82%." Take a long look at the tight construction in Figure D3 (well, probably Figure F5, to be honest) and imagine building that fifty times!

Appendix E discusses a high-impedance probe circuit, based on the Elantec EL2004 350-MHz FET-input buffer amplifier. The resulting probe has a input capacitance of about 4 pF. Again, the tight construction in Figure E2 is impressive.

Appendix F is a brilliant pictorial essay on construction techniques. Figures F1 through F3 (all captioned "No") display a variety of sins. Figure F2 is of historical interest (I admit to feeling old when I have to first describe wirewrap to my students before I can make fun of it). I had never thought of the clip-lead construction in Figure F3 (a creative disaster). Figures F4 (another 556 picture!) and F5 show the prototype avalanche pulser from Appendix D, constructed in Jim's trademark style. Figure F6 shows the settling-time-measurement circuit from Appendix B. Figures F7 to F24 show various high-speed circuits from the main text, demonstrating the attention to shielding and stray capacitance, and the inattention to layout. Smaller and tighter is better. Figure F23 again shows that sometimes the best cable is no cable. Figure F25 shows the good life.

Appendix G contains the FCC forms appropriate for the circuit in Figure 116. See also the contributions of Prof. C. Berry in Figure 117.

Appendix H contains a brief history of "current feedback" (it's older than you think) and an introduction to "Current Feedback Basics" written by William Gross. "So, while the technique is not new, marketing claims notwithstanding, the opportunity is." (There's also a very good discussion of current-feedback amplifiers in Chapter 25 of Jim's first book, written by Sergio Franco.)

Appendix I is documentation for the "enticing" LTC high-frequency amplifier demo board, that is, the good life as suggested in Figure F25.

Finally, Appendix J ends the publication on a humorous note, if the observations contained therein doesn't strike too close to home. Some days, I just don't think Murphy's Law is all that funny.

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Related:

• App Note 47 part 1
• App Note 47 part 2
• App Note 47 part 3
• App Note 47 part 4
• App Note 47 part 6

App Note 47 part 2

The first sections of App Note 47 are "Mr. Murphy's Gallery of High Speed Amplifier Problems" and the "Tutorial Section". Mr. Murphy's Gallery is a expanded and improved version of "The Rogue's Gallery of High Speed Comparator Problems" from App Note 13. The best part of this gallery is the rating system: the average number of phone calls they received per month due to each problem. The winner, of course, with 165 calls per month, is "Excessive Capacitive Load".

The "Tutorial Section" begins with a discussion of termination quality and high-speed pulses (using his new 350ps-rise-time pulse generator from App Note 45: compare Figure 29 with App Note 45 Figure 28). A discussion of probe and probing technique follows, with Figure 31 demonstrating the (quite good) advice that "Sometimes the best probe is no probe" (demonstrated with his trusty Tektronix 556). Much of this section is borrowed from Appendix B of App Note 13.

The section "About Oscilloscopes" includes two pieces: a piece on bandwidth, and a piece on overload performance. The first piece begins with an interesting statement and footnote: "The protracted and intense development effort put toward [oscilloscopes] is perhaps equaled only by the fanaticism devoted to timekeeping (in particular, the marine chronometer received ferocious and abundant amounts of attention)." (Note that Jim wrote this statement almost five years before the publication of Dava Sobel's popular "Longitude" book.) An interesting gallery of oscilloscope pulse responses are shown in Figures 38 through 44. The fastest scope shown (Figure 38) is the Tek 556 with the 1S1 1-GHz sampling plug-in. A Tek 485 is used in Figures 39 through 42, showing the 350-MHz (50-ohm) and 250-MHz (1-megaohm) bandwidths, with several different probes. A 150-MHz Tek 454A (fits under an airline seat!) is used in Figure 43, and, finally, a 50-MHz measurement is shown in Figure 44, using a Tek 556 with a 1A4 plug-in.

The piece on overload performance (Figures 45 through 50, with text beginning on page AN47-22) is borrowed from Box Section A of App Note 10. The next two sections "About Ground Planes" and "About Bypass Capacitors" (Figures 55 through 60) are also borrowed, from Appendix C and Appendix A of App Note 13 (respectively).

Finally, the "Breadboarding Techniques" and "Oscillation" sections include a pictorial tutorial on construction for high-speed circuits in Figures 62 through 65. "More than anything else, breadboarding is an iterative procedure, an odd amalgam of experience guiding an innocent, ignorant, explorative spirit." I often have a hard time convincing people that such a construction technique really works, but it really does! Nice, neat layouts, with lots of straight wiring, often have too much parasitic capacitance, parasitic inductance, and parasitic feedback loops. "Despite the breadboard’s seemingly haphazard construction, the circuit worked well."

Best quote (page AN47-5): "Like all engineering endeavors, high speed circuits can only work if negotiated compromises with nature are arranged. Ignorance of, or contempt for, physical law is a direct route to frustration. Mother Nature laughs at dilettantism and crushes arrogance without even knowing she did it."

I'll discuss the first application sections next time.

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Related:

• App Note 47 part 1
• App Note 47 part 3
• App Note 47 part 4
• App Note 47 part 5
• App Note 47 part 6

App Note 45 part 2

Again, we have a collection of circuits here that captured Jim's imagination in some way or are improvements of circuits from previous app notes.

Figure 18 shows a quartz-stabilized oscillator, which is a different approach from the Hewlett-Packard-inspired oscillators in App Note 43. This circuit achieves 9 ppm distortion (Figure 48 in App Note 43 achieved 3 ppm distortion), but it requires a 4-kHz J-cut crystal.

Figure 19 is a single-cell-powered temperature-compensated crystal oscillator, similar to App Note 15, Figure 9. A boost converter is used to drive the varactor diode with bias voltages up to 4V.

Figure 21 appears to be an improved version of the "Zoo Circuit" V-to-F converter (App Note 23 Figure 16) with even lower power consumption (maximum 90 microamps). Figure 24 is another V-to-F converter, this one with a bipolar input (and a start-up circuit adapted from the Tek 547 trigger circuit).

Figure 27 is a 350-ps rise-time pulse generator. This circuit will be very useful in App Note 47 and other upcoming app notes (and it is much better than the 1-ns pulse generator in App Note 13 Figure D1). The pulse in Figure 28 is very clean, shown on his Tek 556 with the 1S1 sampling plugin. "I'm sorry, but 1GHz is the fastest scope in my house." (See Reference 7.)

Figure 30 is a low-dropout regulator using the LT1123 and the specially design (and now unavailable?) MJE1123 transistor. A germanium 2N4276 is explored as a replacement (but is no easier to obtain!).

Figure 36 is a power supply for a cold-cathode fluorescent lamp. Look at all the bottles! I count 48 of them. Yikes. Although Jim may not know it yet, this application is the beginning of a long-term obsession (or was it an assignment?). More praise for the Tektronix 556 and 547 on the bottom of page AN45-22.

Best quote (from Figure 36, a harbinger of future difficulties): "Do not substitute components."

More than half of the references on page AN45-23 (References 9 to 17) have to do with fetal heart monitoring (as shown in Figure 1). I feel a little sorry for Jim's wife and unborn son at this point. The App Note concludes with a great picture of Michael, perched atop a Tektronix 556.

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Related:

• App Note 45 part 1

App Note 13 part 3

The appendices of App Note 13 include a wealth of practical information. Appendix A talks about bypass capacitors and includes five scope traces that warn of potential troubles. Figure A7 is particularly horrifying. (I wish he named some names here; I'd like to know what specific combination of capacitors caused that shameful ringing. I guess I'll have to experiment myself... Personally, I've been using a combination of tantalum and X7R for bypassing. I really should check it out, as Jim suggests.)

Appendix B further discusses probes and oscilloscopes. Again, he doesn't name any specific makes and models of oscilloscopes, but we can guess what he's using (a Tek 547 and a Tek 556). It's funny how he suggests that the oscilloscope should have 150 MHz of bandwidth, after admitting that "90% of the development work was done with a 50MHz oscilloscope." More space is devoted to discussing probes, FET probes, current probes, and (of course) grounding. I think that I will steal the test circuit in Figure B1 to use at the basis of a lecture demo and/or lab project. It is simple, yet instructive. The picture in Figure B5 shows a wide variety of probe types ("Note the ground strap on the third finger."). 

Appendix C discusses some suggestions for ground planes. In short, use them and love them. 

All three of the above appendices will appear again (in one form or another) in App Note 47.

Appendix D shows an interesting and strange circuit for producing very fast pulses. First comment: the LM301A is only specified for a maximum voltage of 36V. The military-grade version, the LM101A, is specified to 44V. I wonder why he didn't suggest the LM101A? Second comment: the circuit uses a TD-263B tunnel diode! That's cool (it's the right tool for the job), but I don't think that Germanium Power Devices even makes tunnel diodes any more. Does anyone? In Figure D2 and the accompanying caption, we learn that the heretical HP scope that we occasionally see is a 275-MHz unit. (I don't know my HP scopes very well. Can anyone identify this model? Is it an HP 1725A?)

Appendix E discusses high-speed level shifters. Figure E2 shows a TTL-inspired level shift with a 15-volt output. I like figure E3 with the speed-up capacitor and the Baker clamp. I really do have a soft spot in my heart for old logic-circuit topologies. I'm curious about what application requires that power FET switching one amp(!) in 9 nanoseconds in Figure E4.

Best quote (page AN13-27): "Probes are the most overlooked cause of oscilloscope mismeasurement." Yep.

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Related:

• App Note 13 part 1
• App Note 13 part 2