Browse Prior Art Database

Bipolar Pulse Current Source

IP.com Disclosure Number: IPCOM000080713D
Original Publication Date: 1974-Feb-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 3 page(s) / 47K

Publishing Venue

IBM

Related People

Barsotti, RH: AUTHOR [+2]

Abstract

In many applications, it is desirable to have a bipolar current source driver which can charge or discharge a capacitor, or otherwise supply current to a load. For integrating the driver circuit into a monolithic chip, it is desirable to avoid the use of PNP transistors. Also, it is highly desirable that charge and discharge currents are approximately equal or proportioned independent of power supply variations. The illustrated circuit exhibits all of the above features. Assume that the load has a highly capacitive characteristic. The circuit operation is described in terms of discharging and charging such load capacitance.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 53% of the total text.

Page 1 of 3

Bipolar Pulse Current Source

In many applications, it is desirable to have a bipolar current source driver which can charge or discharge a capacitor, or otherwise supply current to a load. For integrating the driver circuit into a monolithic chip, it is desirable to avoid the use of PNP transistors. Also, it is highly desirable that charge and discharge currents are approximately equal or proportioned independent of power supply variations. The illustrated circuit exhibits all of the above features. Assume that the load has a highly capacitive characteristic. The circuit operation is described in terms of discharging and charging such load capacitance.

In the current sink or discharging mode, the current sink I1 predetermines the discharge current amplitude. When input signal A is relatively positive, transistor T1 conducts supplying current I1. As a result, current switch transistor T2 is held to the nonconductive state by reference voltage VR. As such, no current is discharged from the load capacitor. As soon as input voltage A goes negative, T1 switches to nonconductance for switching transistor T2 to current conduction, thereby discharging the load capacitor by current I1.

During a load capacitor charging mode, current source A1 supplies current via capacitive node and diode D1. The current amplitude of source A1, which includes matched resistors R1 and R2, is determined by current sink I3. I3 and I1 are matched current sources such that I1 = I3 for making the charging and discharging current of a load capacitor equal. By altering the ratio of I1 and I3, the charge and discharge current amplitudes can be proportioned. When I3 = I1, and if R1 = R2 so that the feedback voltage is equal, then the current supplied to the capacitive node from A1 is equal to the current...