Differential amplifier

• US 6,252,458 B1
• Filed: 10/28/1999
• Issued: 06/26/2001
• Est. Priority Date: 12/02/1998
• Status: Expired due to Term

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Shibata, Kohei
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): Choe, Henry
• Application Number:
  US09/428,755
• Time in Patent Office: 607 Days
• Field of Search: 330/252, 330/253, 330/257, 330/261
• US Class Current: 330/261
• CPC Class Codes: H03F 2203/45508 the CSC comprising a voltage generating circuit as bias circuit for the CSC
• CPC Class Codes: H03F 2203/45612 the IC comprising one or more input source followers as input stages in the IC
• CPC Class Codes: H03F 2203/45702 the LC comprising two resistors
• CPC Class Codes: H03F 3/45183 Long tailed pairs H03F3/4521, H03F3/45237 take precedence
• CPC Class Codes: H03F 3/45188 Non-folded cascode stages
• CPC Class Codes: H03F 3/45197 Pl types H03F3/45224, H03F3/45251 take precedence
• CPC Class Codes: H03F 3/45704 Controlling the input circuit of the differential amplifier

Abstract

A differential amplifier having an integrated resistance load type differential pair in which a constant current which varies to suppress a small signal gain variation of a resistance load type differential pair caused by variations of circumferential conditions and manufacturing process conditions and a constant current which varies to suppress a limiter amplitude variation of the resistance load type differential pair caused by the variations of the same conditions are mixed at a fixed ratio under a condition which is most frequently used among the circumferential conditions and a condition which is best achieved among the manufacturing process conditions, which is used as a bias current of the differential pair.

Claims

1. A differential amplifier comprising:

an integrated resistance load type differential pair;

a gain variation suppressing type current source for generating a first predetermined constant current to suppress a small signal gain variation of the integrated resistance load type differential pair, caused by variations of circumferential conditions and manufacturing process conditions;

a resistance variation suppressing type current source for generating a second predetermined constant current to suppress a limiter amplitude variation of the integrated resistance load type differential pair, caused by variations of the circumferential conditions and the manufacturing process conditions;

a mixing means connected to the gain variation suppressing type current source and the resistance variation suppressing type current source for mixing the first and second predetermined constant currents mixed at a constant ratio under a condition most frequently used among the circumferential conditions and best achieved among the manufacturing process conditions, and

a bias current source connected to the integrated resistance load type differential pair to provide a constant current mixed by the mixing means as a bias current for the integrated resistance load type differential pair.

2. The differential amplifier as claimed in claim 1 wherein the constant ratio is chosen so that the amounts of the small signal gain variation and the limiter amplitude variation simultaneously fall within their allowable ranges.

3. The differential amplifier as claimed in claim 1 wherein the resistance load type differential pair has cascade transistors between load resistors and transistors composing the differential pair.

4. The differential amplifier as claimed in claim 1;

further comprising another resistance load type differential pair for inputting an output of the former differential pair, and another resistance variation suppressing type current source for generating a constant current to suppress a limiter amplitude variation of the another resistance load type differential pair and connected to be used as the bias current source of the another resistance load type differential pair.

5. The differential amplifier as claimed in claim 4 wherein the (latter) another resistance load type differential pair inputs the output of the former differential pair through one of a voltage dropping source follower or emitter follower.

6. The differential amplifier as claimed in claim 4 wherein current output terminals of the another differential pair are mutually connected with a resistor.

7. The differential amplifier as claimed in claim 5 wherein current output terminals of the another resistance load type differential pair are mutually connected with a resistor.

8. The differential amplifier as claimed in claim 1 further comprising a peak detector and a bottom detector which respectively detect a peak value and a bottom value of an input signal of the differential amplifier, and a voltage divider coupled to the peak detector and the bottom detector to divide outputs of the peak and bottom detectors to generate a threshold signal, the input signal and the threshold signal being applied to the integrated resistance load type differential pair at a first stage thereof.

9. The differential amplifier as claimed in claim 4 further comprising a peak detector and a bottom detector which respectively detect a peak value and a bottom value of an input signal of the differential amplifier and a voltage divider coupled to the peak detector and the bottom detector to divide outputs of the peak and bottom detectors to generate a threshold signal, the input signal and the threshold signal being applied to the integrated resistance type differential pair at a first stage thereof.

10. The differential amplifier as claimed in claim 5 further comprising a peak detector and a bottom detector which respectively detect a peak value and a bottom value of an input signal of the differential amplifier and a voltage divider coupled to the peak detector and the bottom detector to divide outputs of the peak and bottom detectors to generate a threshold signal, the input signal and the threshold signal being applied to the integrated resistance type differential pair at a first stage thereof.

11. The differential amplifier as claimed in claim 6 further comprising a peak detector and a bottom detector which respectively detect a peak value and a bottom value of an input signal of the differential amplifier, and a voltage divider, coupled to the peak detector and the bottom detector to divide outputs of the peak and bottom detectors to generate a threshold signal, the input signal and the threshold signal being applied to the differential pair at a first stage thereof.

12. The differential amplifier as claimed in claim 7 further comprising a peak detector and a bottom detector which respectively detect a peak value and a bottom value of an input signal of the differential amplifier, and a voltage divider coupled to the peak detector and the bottom detector to divide outputs of the peak and bottom detectors to generate a threshold signal, the input signal and the threshold signal being applied to the differential pair at a first stage thereof.

13. The differential amplifier as claimed in claim 1 wherein the bias current source comprises a current mirror.

14. The differential amplifier as claimed in claim 13 wherein the transistors composing the current mirror have cascade transistors.