RAMP/SWEEP GENERATOR J. Ray Hallman Jr. · RAMP/SWEEP GENERATOR J. Ray Hallman, Jr. 1. Introduction...

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NATIONAL RADIO ASTRONOMY OBSERVATORY Green Bank, West Virginia Electronics Division Internal Report No. 87 RAMP/SWEEP GENERATOR J. Ray Hallman Jr. JULY 1969 NUMBER OF COPIES: 100

Transcript of RAMP/SWEEP GENERATOR J. Ray Hallman Jr. · RAMP/SWEEP GENERATOR J. Ray Hallman, Jr. 1. Introduction...

Page 1: RAMP/SWEEP GENERATOR J. Ray Hallman Jr. · RAMP/SWEEP GENERATOR J. Ray Hallman, Jr. 1. Introduction The radio interference staff has expressed a need for a precise slow-sweep generator

NATIONAL RADIO ASTRONOMY OBSERVATORYGreen Bank, West Virginia

Electronics Division Internal Report No. 87

RAMP/SWEEP GENERATOR

J. Ray Hallman Jr.

JULY 1969

NUMBER OF COPIES: 100

Page 2: RAMP/SWEEP GENERATOR J. Ray Hallman Jr. · RAMP/SWEEP GENERATOR J. Ray Hallman, Jr. 1. Introduction The radio interference staff has expressed a need for a precise slow-sweep generator

RAMP/SWEEP GENERATOR

J. Ray Hallman, Jr.

1. Introduction

The radio interference staff has expressed a need for a precise slow-sweep

generator for use with the frequency spectrum analyzer recording system in the in-

terference van. To meet this need a ramp/sweep generator has just been completed.

I wish to thank Mr. R. Weimer for the thoughtful suggestions concerning the

circuits.

2. General

The ramp/sweep generator must be capable of

(1) Producing a ramp that sweeps from 0 volts to +15 volts

with a period adjustable from 1 minute to 11 minutes.

(2) Offering a test mode in which the ramp period is reduced

by an order of magnitude for testing the spectrum analyzer

recording system.

(3 Producing a -5 volt pulse during retrace for blanking the

spectrum analyzer.

(4) Offering both single sweep and automatic recurrent sweep,

both with push-button start.

(5) Offering a means of manually setting the sweep to any level

by means of a manual position knob.

(6) Offering a means of stopping and holding the ramp at any

position with a toggle switch.

These requirements are met by the equipment described in this report.

Page 3: RAMP/SWEEP GENERATOR J. Ray Hallman Jr. · RAMP/SWEEP GENERATOR J. Ray Hallman, Jr. 1. Introduction The radio interference staff has expressed a need for a precise slow-sweep generator

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3. Description. of the Ram Sweep Generator

The ramp is generated by an operational amplifier integrator circuit. The

op-amp is an Analog Devices 140A which has a FET input offering extremely low

integrator drift during the hold function.

The input current to the integrator is switched during normal operation by

2N4393 FET switch transistors. Four input current circuits are provided, one each

for the following:

(1) Run mode — the ramp period is adjustable from

1 minute to 11 minutes.

(2) Test mode — the ramp period is adjustable from

. 1 minute to 1. 1 minute.

(3) Retrace mode — retraces in 5 seconds to start of

sweep.

(4) 0 Volt hold mode — holds at 0 volts at start of sweep

when equipment is operated in single sweep.

The FET switches are controlled by four driver circuits that convert the 0,

+5 logic levels to -10, +20 voltage levels for driving the FET' s.

There are three integrated circuit "chips" supplying all necessary control

functions and timing. These consist of 2 flip-flops and 8 two-input NAND gates.

The output of the integrator is buffered with an Analog Devices 118 operating

as a voltage follower before going to the level meter and outside world. The mini-

mum load impedance at the output "BNC" should not be less than about 4 K ohms.

In manual mode the buffer amplifier input is switched to the manual position

pot and functions as a precision voltage source.

Blanking is provided during retrace. It is a -5 volt level during retrace.

The level returns to ground level through 510 ohms after retrace is completed.

Block and circuit diagrams follow.

Page 4: RAMP/SWEEP GENERATOR J. Ray Hallman Jr. · RAMP/SWEEP GENERATOR J. Ray Hallman, Jr. 1. Introduction The radio interference staff has expressed a need for a precise slow-sweep generator

-10 0

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Page 5: RAMP/SWEEP GENERATOR J. Ray Hallman Jr. · RAMP/SWEEP GENERATOR J. Ray Hallman, Jr. 1. Introduction The radio interference staff has expressed a need for a precise slow-sweep generator

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Page 6: RAMP/SWEEP GENERATOR J. Ray Hallman Jr. · RAMP/SWEEP GENERATOR J. Ray Hallman, Jr. 1. Introduction The radio interference staff has expressed a need for a precise slow-sweep generator

+20V

-I0V

510

+5VFROM 1N4151INTEGRATOR >-M----

OUTPUT IK/k 5102 3904

2N3904 4.7K SWITCHD' OUTPUT

LEVELADJUST5K

7.5K2N3904

147015.1K

2 N3906

[GOES +5WHEN15 VOLTSDETECTED+5V

2N3906LINEAR OUTPUTg* CENTERS TO

+5V WHENHOLD POINTIS REACHED

SWITCHOUTPUT(GOES +5

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FROM 1N4151INTEGRATOR > 14 •OUTPUT

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5

END OF SWEEP DETECTOR

END OF RETRACE DETECTOR

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INPUT

FET GATE DRIVER

+20V4

10K

2N 3904

LOGICINPUT

OM.

BLANKING AMPLIFIER

-10 V

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End of Sweep Detector

The end of sweep detector consists of a difference am.plifier input and two

transistor level shifting network. The input to the difference amplifier is through

a diode that serves to isolate the detector and integrator during normal sweep

and also protect the input base emitter junction. The detector trip point is adjust-

able to ± 2. 5 volts of the design level of 15 volts.

During normal operation when the integrator sweeps up to +15 volts the

1N4151 diode conducts and the current changes to the input transistor as it goes into

conduction. This is a linear transition the speed of which is a function of the ramp

rate. But this transition is fast after being amplified by the two transistor level

shifter. The output of the level shifter is (0, +5) volts and interfaces directly with

the IC logic "chips". The output level goes to +5 volts when the +15 volt end of the

sweep level is reached, thus, reseting the sweep/retrace flip-flop in the logic con-

trol section.

End of Retrace Detector

The operation of this detector is similar to the one just discussed except that

the trip point is designed to be 0 volts. Notice that the input diode is reversed such

that it also does not conduct until the end of retrace is reached. Also, the input tran-

sistor is held normally conducting by the 27 K resistor and the output phase is inverted

by taking the level shifter input from the input transistor collector circuit instead of

the emitter coupled stage as done in the end of sweep detector.

The end of retrace detector has also a second output referred to as a linear

output since its output varies more slowly than the logic output. When the ramp/sweep

generator is operated in single sweep mode, at the end of one sweep cycle the 0 volt

hold flip-flop is set along with the sweep/retrace flip-flop. This switches the 0 volt

hold gate closing the path between the detector linear output and the integrator input.

The operation is such that when the integrator output is above 0 volts the linear output

goes a maximum of 5 volt positive relative to the integrator reference so that the inte-

grator drives down. If the integrator output is below 0 volts, then the linear output

goes a maximum of 5 volts negative and the integrator drives up until it reaches 0

volts at which the linear output balances to the reference level of the integrator.

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Thus, through this action the device "servos" to 0 volts and holds to this level with

a 5 second time constant. It may be of importance to note that the point at which the

loop balances is about 40 millivolts higher than the 0 volt trip point. This allows

the detector logic output to return to ground, thus removing the SET level from the

two control flip-flops so that the hold flip-flop can be instantaneously reset.

Page 10: RAMP/SWEEP GENERATOR J. Ray Hallman Jr. · RAMP/SWEEP GENERATOR J. Ray Hallman, Jr. 1. Introduction The radio interference staff has expressed a need for a precise slow-sweep generator

. Operation

The operation of each control is now explained. Refer to the last page of this

report for a picture showing control locations.

Power Switch Applies power to the circuits.

Run/Test Switch With the toggle in RUN, the ramp period is

adjustable from 1 minute to 11 minutes

using the ramp rate control. When in TEST,

the period is . 1 minute to 1. 1 minutes.

In HOLD the integrator unconditionally holds

the ramp/sweep output to whatever level it

was when the switch was put in this position.

When it is desired to return to normal opera-

tion, the switch is negotiated to NORMAL and

the integrator continues from this level.

Hold/Normal • • OOOOOOO • • • • •

Ramp Rate Control .... . .. Sets ramp period as explained under run/test

switch.

Start Sweep Button .. • • • • • • • Whenever this equipment is first put into auto-

matic operation and anytime when in single

sweep operation, the button can be pushed to

initiate the sweep.

Manual/Single/Auto Switch .. Determines the primary mode of operation as

follows. When in MAN the output level is

manually controlled by turning the manual posi-

tion control. In SINGLE a single ramp sweep

is produced when the start button is pushed.

When in AUTO the recurrent sweep is produced

when the start button is depressed.

Page 11: RAMP/SWEEP GENERATOR J. Ray Hallman Jr. · RAMP/SWEEP GENERATOR J. Ray Hallman, Jr. 1. Introduction The radio interference staff has expressed a need for a precise slow-sweep generator

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4. Operation (continued):

Manual Position Control .... Explained under manual/single/auto switch.

The knob decade indicates the percent of full-

scale sweep.

Ramp Level Meter

• .

.

Indicates instantaneous ramp output level in

terms of percent of maximum output level.

There are two internal adjustment pots accessible from the bottom that allow

fine adjustment of the ramp level at both end of sweep and end of retrace. It is possi-

ble to adjust ± 2. 5 volts of the design levels of 0 and +15 volts. Normally, after

initial setting, these adjustments can be locked in place since no additional adjustment

is necessary.

Page 12: RAMP/SWEEP GENERATOR J. Ray Hallman Jr. · RAMP/SWEEP GENERATOR J. Ray Hallman, Jr. 1. Introduction The radio interference staff has expressed a need for a precise slow-sweep generator

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