DIGITALLY PROGRAMMABLE TRANSCONDUCTANCE AMPLIFIER AND MIXED-SIGNAL CIRCUIT USING THE SAME
The present invention relates to an trans-conductance amplifier, cooperating with a digital programmable current mirrors, can be applied to digital programmable current-mode integrated circuits, voltage control oscillators, adaptive frequency adjust mechanism, adaptive continuous analog filters via the corresponding trans-conductance adaptation controlled by the digital control signals. The present invention disclosed a digital programmable current mirror suitable for the second stage of the trans-conductance amplifier so as to reform the fixed gain trans-conductance amplifier to be digitally programmable.
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1. Field of the invention
The present invention relates to a trans-conductance amplifier, and more particularly to, a digitally programmable trans-conductance amplifier and mixed signal circuits using the same.
2. Description of the Prior Art
The conventional current mirror for the trans-conductance amplifier is shown in
As suggested in U.S. Pat. No. 6,466,100 B2 and 6,462,527 B1, in both of the prior arts digitally control signals are used to control and switch the counting of parallel transistors so as to change the equivalent widths of the transistors and a variable current source is used to provide the bias current of the output stage. The drawbacks of these two prior arts are that the variation of the bias current of the output stage according to the control signal is significant and thus their output impedance varies significantly.
Also, in U.S. Pat. No. 6,456,158 B1 suggested a trans-conductance amplifier, which is digitally programmable, however, a plurality of resistors invite noises and at output stage, inevitably, there needs a current follower to enhance the output stage to be high impedance.
Hence, the present invention provides a solution for a trans-conductance amplifier, particularly a digitally programmable trans-conductance amplifier, to address the issue of the conventional programmable current mirrors. The present invention is assumed that the output current is a constant and the switch can be turned on or off to change the reference current and the widths of the transistors so as to achieve the goal for programmable current mirrors. The disclosures of the present invention suggest reforming all current mirrors to be programmable and suitable for the second stage of the trans-conductance amplifier which reforms the trans-conductance amplifier with fixed gain to be of variable trans-conductance so as to let the mixed mode signal circuit using the same with variable gain can base on the feedback loop to achieve the goal of setting the corresponding parameters to be constant.
SUMMARY OF THE INVENTIONIn view of the disadvantages of prior art, the primary object of the present invention relates a digitally programmable trans-conductance amplifier using digitally programmable active current mirror so as to achieve high and constant impedance and at the same time achieve precise trans-conductance.
Preferably, said digitally programmable trans-conductance amplifier comprises: an active current mirror circuit, said active current mirror circuit comprises: a reference system and a variable current source for providing the bias current in the reference system; an output side current mirror and a constant current source for providing the bias current at the output side; a plurality of switches; a first node and a second node, said first node and said second note are disposed at the intersection between said reference system and the variable current source for providing the bias current in the reference system, and at the intersection between said active current mirror and the fixed current source at output side respectively; and a constant trans-conductance amplifier, wherein the output of said amplifier is interconnected with said first node.
Preferably, as illustrated in
The hypothesis for the above formula is, VGS1 and VGS2 are the same and to be a constant value. Preferably, the output DC bias current is a constant current. To achieve the goal, the current source IVAR has to be changed according to the width variation of a transistor 211 so as to keep VGS1 constant, and then VGS1 and VGS2 are identical to each other. If the current source IVAR follows the change of the width of the transistor M1, we need a corresponding variable current source and further need a plurality of switches to control the width of the transistor M1.
The present invention relates to using a variable current source and transistor array switches to control the effective widths of the transistors at reference side. And by changing the trans-conductance value at the reference side of the transistors the current gain of the current mirror can be further varied, and the current gain is according to the change of the trans-conductance of the whole circuitry.
As illustrated in
Further scope of applicability of the present application will become more apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
The present invention will become readily understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention and wherein:
The following descriptions are of exemplary embodiments only, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the following description provides a convenient illustration for implementing exemplary embodiments of the invention. Various changes to the described embodiments may be made in the function and arrangement of the elements described. For your esteemed members of reviewing committee to further understand and recognize the fulfilled functions and structural characteristics of the invention, several exemplary embodiments cooperating with detailed description are presented as the follows.
Preferably, as suggested by
As illustrated in
In
Since the sizes for switch 506 are the same and the corresponding action is to simultaneously turn on and off the transistor switches, as a result we can use the same set of transistor switches to share 501 and 502, and the concept of sharing circuits brings the benefit of saving the die size, as illustrated in
By the advantage of the disclosures of the present invention, skilled persons can use variable reference current sources and switch arrays, accordingly all the current mirrors can be reformed to be digitally programmable current mirrors accepting the digital signal control, as illustrated in
Referring to
In the present invention, the digital voltage control signals are used to complete the feedback adjusting mechanism and are used for successive approximation. As illustrated by
The invention being thus aforesaid, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
Claims
1. A digitally programmable trans-conductance amplifier, comprising:
- an active current mirror circuit, said mirror circuit comprising: a reference system; a first current source for providing said reference system a bias current; an output side current mirror; a second current source for providing the bias current at the output side; a plurality of switches; a first node and a second node, said two nodes are respectfully disposed at the intersection between said reference system and said first current source and at the intersection between said output side current mirror and said second current source; and
- a constant trans-conductance amplifier, wherein the output of said amplifier is interconnected with said first node.
2. The digitally programmable trans-conductance amplifier as set forth in claim 1, wherein said first current source is a constant current source.
3. The digitally programmable trans-conductance amplifier as set forth in claim 1, wherein said second current source is a variable current source.
4. The digitally programmable trans-conductance amplifier as set forth in claim 3, wherein said variable current source is controlled by said a plurality of switches.
5. The digitally programmable trans-conductance amplifier as set forth in claim 1, wherein the trans-conductance value of said amplifier can be expressed as: the constant trans-conductance multiplied by the ratio of said second current source and said first current source.
6. The digitally programmable trans-conductance amplifier as set forth in claim 1, wherein the first current source is made of transistors.
7. The digitally programmable trans-conductance amplifier as set forth in claim 1, wherein the second current source is made of transistors.
8. The digitally programmable trans-conductance amplifier as set forth in claims 6 and 7, wherein the trans-conductance value of said amplifier can be expressed as: the constant trans-conductance multiplied by the ratio of the transistors of the second current source and the first current source.
9. The digitally programmable trans-conductance amplifier as set forth in claim 6, wherein the transistors are cascoded.
10. The digitally programmable trans-conductance amplifier as set forth in claim 7, wherein the transistors are cascoded.
11. The digitally programmable trans-conductance amplifier as set forth in claim 1, wherein the digitally programmable trans-conductance amplifier can be applied to the closed loop in a mixed signal circuit.
12. The digitally programmable trans-conductance amplifier as set forth in claim 11, wherein the mixed signal circuit is a filter.
Type: Application
Filed: Aug 5, 2008
Publication Date: Jan 7, 2010
Applicant: HOLTEK SEMICONDUCTOR INC. (Hsinchu)
Inventor: HUNG-CHANG CHEN (Changhua County)
Application Number: 12/185,880
International Classification: H03F 3/45 (20060101);