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4.2. INITIAL TESTING AND OBSERVATION OF

PULSE WAVEFORMS

See Sections 6.1 and 6.2 for test performance data.

4.3. CONNECTOR DATA

CN1 Input, BNC Connector AC-coupled linear gate input;

input impedance >50000: input rated voltage range 0.2 to

10 V; maximum input 12 V. To minimize reflections when

driving from low impedance sources into this connector, a

terminator equal to the characteristic impedance of the

driving cable should be shunted from this connector to

ground.

CN2 Linear Gate Output, BNC Connector DC-coupled out

put; output impedance <20,; positive output signals only

with rated range of 0.2 to 10 V; maximum output 12 V.

TP2 Linear Gate Output Test Point Osci l loscope test point

for monitoring signal on l inear gate output BNC connector

CN2. This test point has 470J2 series resistor connecting it

toCN2.

CN3 Enable Input, BNC Connector

DC-coupled; input

impedance 100012; requires a positive 2-V pulse; maximum

input 20 V.

CN4 DC Inhibit Input, BNC Connector DC-coupled; input

impedance 65012; requires a positive 4-V pulse or dc level;

maximum input 20 V.

4.4. TYPICAL OPERATING CONSIDERATIONS

In the Normal mode the Linear Gate is opened, i.e., passes

input signals, with the application of a positive pulse on the

Enable input. The duration that the Linear Gate will remain

open is normally continuously variable from 0.3 to 4 jusec

with the front panel control. For other pulse widths refer to

Section 6.2.

Figure 4.1 illustrates the gating action of the Linear Gate.

Notice that only the positive portion of the input signal is

passed through the Linear Gate. The Linear Gate has an

internal pedestal adjustment that allows the pedestal to be

reduced to a negligible value (refer to Section 6.2 for

adjustment procedure). Figure 4.2 shows the output of the

Linear Gate with the pedestal properly adjusted and

improperly adjusted.

The Linear Gate is usually operated in the normally closed

mode with both input and output ac-coupled. Two variants

of this mode are possible; gate operating normally open, i.e.,

normally passes al l input signals except when accompanied

by an enable or inhibit pulse, and gate dc-coupled operating

either normally closed or normally open. Operation in the

second mode requires modification to the actual etched

circuit board. For dc operation the input and output

capacitors C1 and C6 must be replaced with jumper wires

•H+f

-H-

"Input"

1-H

Output

ff-

Fig. 4.1. Gating Action of Linear Gate.

-Hi-H

11 1 L 1 1 1 1

1 If IJ

Ji l l

1 1 n

Sea

1 1 1 1 '

e; IOC

50C

Mi l

mV/c

nsec/

-ntr

(a) Pedestal Properly Adjusted.

f i l l

1 I

1 1 1 1

1 1

I I I 1 1 1

I I I !

t i l l

1 1 1 1

Mi l

Sea

le: Id

D mV/

D nsec/

(b) Pedestal Improperly Adjusted.

Fig. 4.2. Output of Linear Gate.

for a dc connection. With this arrangement a small dc offset

voltage from input to output wil l be observed, approximately

160 mV, and must be considered in the connection of the

gate to the input and output equipment.

For operation in the Inhibit mode, al l input signals wil l be

passed except when an inhibit signal is applied to either the

Enable input or to the DC Inhibit Input. The particular.in

put depends on the position of the mode switch. Enable in

put for Pulse Inhibit position and DC Inhibit Input for the

DC Inhibit position (refer to Section 4.1). With the mode

switch set to DC Inhibit and no input to the DC Inhibit In

put connector, the linear gate wil l pass all input signals. This

can be a very useful mode for setting up experiments since

the proper timing of the input signal to the Enable input is

not necessary to get an output signal. A slight difference in

the pedestal magnitude may be noticed when changing

modes from Normal to DC Inhibit. The pedestal is normally

adjusted for minimum in the Normal mode, but may be

adjusted to suit the experiment in any mode desired.