Miscellaneous active electrical nonlinear devices – circuits – and – Specific signal discriminating without subsequent control – By amplitude
Reexamination Certificate
1999-03-03
2001-02-06
Callahan, Timothy P. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific signal discriminating without subsequent control
By amplitude
C327S538000, C327S540000, C323S312000
Reexamination Certificate
active
06184723
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a linear direct voltage to proportional to absolute temperature (PTAT) current converter for use in conjunction with a variable-gain amplifier (VGA) to convert a variable control input voltage to a current proportional to absolute temperature in a linear manner.
BACKGROUND AND BRIEF DESCRIPTION OF THE PRIOR ART
Generally, control of VGAs involves a linear voltage control range, generally about two volts, and provides only a single control slope. In addition, the prior art control voltage is normally distorted in order to provide a linear transfer function in dB at the VGA output. Other approaches required to transform the control voltage into a PTAT current which will serve as the tail current of the amplifier. This PTAT current conversion requires a two step operation, the first operation being to convert the control voltage to a current which is not proportional to absolute temperature and then to translate that current to a proportionality to absolute temperature (a PTAT current) by multiplying that current by a current which is proportional to absolute temperature and dividing the product by a current which is not proportional to absolute temperature. These operations are circuitry intensive. Furthermore, this type of control also normally has a limited dynamic range characteristic and does not guarantee a constant gain control slope.
SUMMARY OF THE INVENTION
In accordance with the present invention, the above described disadvantages of the prior art are minimized and there is provided a current converter which directly and in a single step generates a PTAT current from an input voltage that is linear relative to a wide range of input voltages, this PTAT current also being controllable with appropriate component design of the circuitry to change the slope of the PTAT current being produced after a predetermined input voltage has been reached and exceeded. The converter in accordance with the present invention provides a direct voltage to PTAT current conversion which allows for easy control of the gain slopes as well as maximum linear dynamic range by using the current not as the tail current of the amplifier, but rather to generate an exponential PTAT current by the use of a simple current mirror, the current which will be mirrored directly into the VGA core.
Briefly, the above is accomplished by providing a plurality of differential transistor amplifier pairs, one of the transistors of each pair being designated a reference transistor and the other transistor being designated a non-reference transistor. Current is concurrently fed to the conduction path of each transistor pair by a current source transistor, there being a separate such current source for each transistor pair. Each current source is designed to provide an amount of current when conductive based upon the design thereof. In general, each of the current sources will provide the same amount of current when energized. However, it is contemplated that the geometry of certain ones of the current sources can be fabricated to provide a different current output relative to other current sources to provide a change in the slope of the output PTAT current. Each current source is driven by a standard PTAT current generator to provide a PTAT current output.
The control electrodes of the non-reference transistors are each connected to the input which is the control voltage discussed hereinabove. The control electrodes of the reference transistors are each coupled to a different reference input voltage. The reference voltages define a range of voltages within which the system is to operate with each of the different reference input voltages being set at a different portion of this range whereby the totality of the reference transistors cover the entire range of voltages. The opposite end of the current path of each of the non-reference transistors is coupled to the same output line whereby the outputs of the non-reference transistors are added together and supplied to an output. The opposite end of the current path of each of the reference transistors is coupled to the same output line which is a different output line with the current applied thereto not generally being used.
In operation, one or the other of each differential transistor pair is conductive. As the input voltage to the system increases but is below the reference voltage at the gate of the non-reference transistor set to the lowest reference voltage, all of the reference transistors will conduct. When the input voltage increases to that of the lowest reference voltage and beyond, the non-reference transistor coupled to the reference transistor set to the lowest reference voltage will conduct and increase conduction with the paired reference transistor concurrently ceasing conduction. As the input voltage increases to that of the next lowest reference voltage and beyond, the non-reference transistor coupled to the reference transistor set to the next lowest reference voltage will conduct and increase conduction with the paired reference transistor concurrently ceasing conduction. The is operation continues from transistor pair to transistor pair as the input voltage increases with the summed output of the non-reference transistors providing a linear output with slope determined by the geometry of the current source transistors. Assuming that these geometries are the same, then the slope of the output current is linear and constant. The slope can be changed by altering the geometry of certain ones of the current source transistors whereby such current source transistors with altered geometry provide a different current to the associated transistor pair relative to the current provided by other current source transistors of the system. This output current will then be summed with a fixed PTAT current, as shown in
FIG. 5
, through resistor RDAC, hence controlling the V
BE
s of both transistors Q
1
and Q
2
. The output of transistor Q
2
is an exponential PTAT current which is a function of the input control voltage.
REFERENCES:
patent: 3617916 (1971-11-01), Smith
patent: 4586155 (1986-04-01), Gilbert
patent: 4965528 (1990-10-01), Okanobu
patent: 5345185 (1994-09-01), Gilbert
patent: 5463332 (1995-10-01), Yee et al.
patent: 5867062 (1999-02-01), Kuduo
Abuzaid Maher A.
Frechette Michel
Brady III Wade James
Callahan Timothy P.
Luu An T.
Neerings Ronald O.
Telecky , Jr. Frederick J.
LandOfFree
Direct voltage to PTAT current converter for multiple gain... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Direct voltage to PTAT current converter for multiple gain..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Direct voltage to PTAT current converter for multiple gain... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2604822