Logarithmic Video Amplifier

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10. THE PC36-1 TEST BOARD

ANADYNE used this test board to build the prototype DLVA unit from which the photographs and

data of Figs. 10(c) - 10(h) were taken. A block diagram of our test apparatus is shown in Fig.

10(l). It may be useful to duplicate our setup as closely as possible to start with. We have listed

below in two categories the components required to duplicate our PC board. We suggest that you

initially use our values for the components in List A. The optimum values for the components in

List B will depend on your particular detector, output cable or load, regulators, and (in the case of

R4, R5, and R9), on the LVA IC. The values for these components should be selected as

described in the Application Notes. For purposes of comparison, we have also shown below the

values of our List B components.

Please note that the optimum values of components, especially those affecting pulse-shape, are

sensitive both to the board layout and the load characteristics. The general pulse-shaping

approaches which are detailed in section 4 of these Application Notes should be your final guide.

However, if a fairly fast rise-time and good recovery are desired using this test PC board, we have

found that the component values given below yield good results when driving a 93-ohm resistive

load on the board. A scope probe was used to examine the waveforms.

You may also note that some of the decoupling caps used for optimum recovery with this board

are quite large. Much smaller decoupling caps can be used in properly-designed compact layouts.

(use our values to start) (select per App. Notes)

We cut the board trace from pin 20 to speed up the output. C18, R19, and C19 are used only with

the pinout number shown above. Trimming about 1" of RG174 coax may be useful in selecting the

value of C18.

Recovery Nets Used

(with a HEROTEK 2 to 18 GHz coaxial tunnel diode detector)