![]() +12V is available from the A1A3 PC board, but I chose to use a separate 7812 regulator to avoid drawing too much current from the smaller 78L12 at U1. Presented by the buffer amplifier doesn't appreciably lower the amplitude available to the 5-MHz divider stage (see plot below). ![]() The 10811 is otherwise loaded by 511 ohms in this circuit, and the additional 400 ohms Taking advantage of this, I used aģ30-ohm resistor in place of R10 in the schematic above, with an 82-ohm resistor between the R10/C5 junction and the 10811's output pin (1, see photo below at left). Input impedance is reasonably high, as typical of other common-emitter designs. Transistor choices are equally uncritical, with a 2N5109 at Q1 and a 2N3906 at Q2 in my version of the circuit. Gain is influenced chiefly by the transformer's turns ratio I used a Mini-Circuits T13-1T transformer in my implementation. The LED specified by Bruce is a superbright part with a 2.0-volt typical forward drop, but I used a random part from the junk box with a forward drop closer to 1.7 volts. DC bias stabilization is provided by a PNP stage with a well-filtered LED reference. In Bruce'sĬircuit, the traditional common-base Norton scheme gives way to a common-emitter layout, with the transformer feedback element still present in the collectorĪnd emitter legs. This particular amplifier circuit is a variation on David Norton's "noiseless feedback" topology from the early 1970s. Norton, US Patent 3,891,934, June 1975 (expired)Ĭlifton Laboratories' Z10040B Norton Noiseless Feedback Amplifier kit by Jack Smith, K8ZOA - great source of app notes and design information Transistor Amplifier with Impedance Matching Transformer, David E. New Norton-Rohde Feedback Amplifiers by Dallas Lankford HP 0105-6100 assembly schematic, used for 10811-60109 OCXO installation in HP 5061A, 5065A, 105B, and other instrumentsīruce's page on low-phase noise OCXO buffer amplifiers at Ĭommon-Base Transformer Feedback Norton Amplifiers by Dallas Lankford Bruce's amplifier is a good candidate for this application. A buffer amplifier is needed to keep from loading the 10811 excessively, to avoid injection-locking problems,Īnd to keep external signals out of the clock's control loop. Many 5061As haveīeen upgraded in the field with the 10 MHz HP 10811-60109 OCXO from the 5061B model, but unlike "real" HP 5061Bs, the upgraded models didn't provide a 10 MHz The prototype characterized here was used to add a 10 MHz output jack to an HP 5061A cesium-beam standard. These attributes make the circuit well-suited for use in buffer amplifier applications, where an internal signal needs to be routed externally Isolation at minimal component cost, along with exceptionally good residual phase-noise performance. This circuit, based on a design by Bruce Griffiths, provides a small amount of gain with about 40 dB of reverse This page describes a common-emitter HF amplifier with transformer feedback and active bias stabilization. Notes on Common-Emitter Transformer Feedback Amplifiers
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