Circuit technique uses a signal diode as a series current-pass element. Technique is applied to the design of a biased amplifier circuit and a nanosecond-pulse stretcher circuit

Larsen, R. N.

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September 1969	 Brief 69-10445 
AEC-NASA TECH BRIEF 
TES
AEC-NASA Tech Briefs describe innovations resulting from the research and development program 
of the U.S. AEC or from AEC-NASA interagency efforts. They are issued to encourage commercial 
application. Tech Briefs are published by NASA and may be purchased, at 15 cents each, from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Current-Switching Technique for Analog Pulse Circuits
.
Fig. 1. Diode-current switch driven from a high-impedance source (Is). 
This circuit gives improved transfer-function linearity above the threshold. 
A new circuit technique is analyzed both theo-
retically and experimentally (1); its principle is use of 
a signal diode as a series current-pass element. This 
technique is applied to the design of two circuits: a 
biased amplifier and a nanosecond-pulse stretcher. 
In the design of analog pulse circuits, the transfer 
function of the circuit is generally of prime impor-
tance: in the design of a linear amplifier, for example, 
an output is desired that is truly a linear function of 
the output. The input parameter may be in terms of
voltage, current, or charge; the output parameter 
need not be the same; the amplifier transfer function 
could, for example, be voltage output versus charge 
input. Whichever parameters are used they must be 
linearly related over the dynamic range of the circuit. 
The electronic components used in design of analog 
circuits (vacuum tubes, transistors, diodes) do not 
have linear voltage-transfer functions. Circuit linearity 
is usually achieved by such techniques as negative 
feedback through linear components such as resistors 
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and capacitors; this technique has proved quite satis-
factory with linear amplifiers. However, negative feed-
back does not always give the best circuit performance 
with other types of analog circuits Such as a biased 
amplifier; in this case, the transfer function is zero 
up to a specified input threshold and is linearly re-
lated to the input above this threshold. Such a transfer 
function is useful when pulses below a specified input 
threshold are of no interest. 
An important characteristic of such a transfer func-
tion is the "sharpness" of the threshold. There are 
several techniques for improving this characteristic; 
the method investigated (I) utilizes the current-
transfer characteristics of a junction-signal-diode 
switching circuit. 
Since the diode is a two-terminal device, the cur-
rent into the diode obviously equals the current out 
of it, and the current input and output are linearly 
related. Often a biased switching circuit is used. 
However, since the diode does not have ideal V-i 
characteristics, the output is not a linear function of 
the input, especially near the point where the diode 
begins conduction; this is so because the voltage-
attenuation across the diode is a nonlinear function 
of the current through it. 
The effect of the nonlinear V-i characteristics of 
the diode can be reduced by use of a simple current-
switching circuit (fig. 1). In this circuit, diode D 1 is 
normally conductive, D 2 is nonconductive, and the 
output current is zero for all values of 1 <
	
When 
1 exceeds 
'b' diode D 1 switches off, and the input-
signal current flows through diode D 2. This current 
(Islb) flows through D 2 regardless of the V-I charac-
teristics of D 2, even when the input signal barely 
exceeds the bias current. The output (current) is then
linearly related to the input (current) over a much 
greater dynamic range than the conventional biased 
switching circuit. 
Several current-switching circuits based on this 
principle are investigated both theoretically and ex-
perimentally (1), as well as their advantages and 
limitations relative to conventional circuits. 
Reference: 
1. R. N. Larsen, "A new current switching technique 
for analog pulse circuits" (Argonne National Lab-
oratory, May 1968). 
Notes: 
1. Designers or manufacturers of computer or pro-
cess-control systems may be interested. 
2. Inquiries concerning this information may be di-
rected to:
Office of Industrial Cooperation 
Argonne National Laboratory 
9700 South Cass Avenue 
Argonne, Illinois 60439 
Reference: B69-10445 
Source: R. N. Larsen 
Electronics Division 
(ARG- 10479) 
Patent status: 
Inquiries concerning rights for commercial use of 
this innovation may be made to: 
Mr. George H. Lee, Chief 
Chicago Patent Group 
U.S. Atomic Energy Commission 
Chicago Operations Office 
9800 South Cass Avenue 
Argonne, Illinois 60439 
Brief 69-10445	 Category 01


Current-switching technique for analog pulse circuits

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