CLCOK DRIVER CIRCUIT
Clock driver circuit having upper and lower transistors1 and upper and lower transistors2. Voltage node1 coupled to electrodes of upper transistor1 and upper transistor2. Voltage node2 coupled to electrodes of lower transistor1 and lower transistor2. Coupling transistor1 couples another electrode of upper transistor1 to another electrode of lower transistor2. Coupling transistor2 couples another electrode of upper transistor2 to another electrode of lower transistor1. Two series1 capacitors couple the another electrode of upper transistor1 to the another electrode of lower transistor1. Two series2 capacitors couple the another electrode of upper transistor2 to the another electrode of lower transistor2. Node intermediate the two series2 capacitors provides in-phase clock output. Node intermediate the two series1 capacitors provides anti-phase clock output. In-phase clock input is coupled to control inputs of upper transistor1, coupling transistor1 and lower transistor1. Anti-phase clock input is coupled to control inputs of upper transistors2, coupling transistor2 and lower transistor2.
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The present invention relates generally to clock driver circuits.
BACKGROUND OF THE INVENTIONDifferential clock drivers are normally used to drive relatively small loads. Capacitive coupling is widely used to enable high data or clock rate interconnection between circuits, such as integrated circuits (ICs). Capacitive coupling (by use of coupling capacitors) typically simplifies circuit design by blocking direct current (D.C.) biasing from being superimposed at output lines, and thus, being supplied to a load. Capacitive coupling also can be used to isolate ground connections between subsystems for noise isolation purposes. However, although capacitive coupling is beneficial when used, for instance, in a differential clock driver circuit, their supply voltage charge to zero voltage discharge may affect the bandwidth of the driver. To overcome this potential bandwidth restriction, differential clock drivers can be configured to have increased peak currents at their outputs to thereby more rapidly charge and discharge their coupling capacitors. As a result, prior art differential clock drivers coupled to respective loads by respective coupling capacitors are typically configured and operated by compromising between clock speed, signal quality and power consumption.
In order that the invention may be readily understood and put into practical effect, reference will now be made to exemplary embodiments as illustrated with reference to the accompanying figures, wherein like reference numbers refer to identical or functionally similar elements throughout the separate views. The figures together with a detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, in accordance with the present invention, where:
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
DETAILED DESCRIPTIONBefore describing in detail embodiments that are in accordance with the present invention, it should be observed that the embodiments reside primarily in circuit components. Accordingly, the circuit components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.
In this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” “including,” “includes,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that circuit components that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such a circuit component. An element proceeded by “comprises . . . a” does not, without more constraints, preclude the existence of additional identical elements in the circuit that comprises the element.
Referring to
The differential clock driver 110 also has two outputs, the first one being an in-phase clock signal output VOP, and a second one being an anti-phase clock signal output VON. A first coupling capacitor CC1 has an input electrode coupled to the in-phase clock signal output VOP, a second electrode of the first coupling capacitor CC1 provides a coupled in-phase output Vout that is coupled to a first load 120. A second coupling capacitor CC2 has an input electrode coupled to the anti-phase clock signal output VON, a second electrode of the second coupling capacitor CC2 provides a coupled anti-phase output Voutb that is coupled to a second load 130. As will be apparent to a person skilled in the art, both loads 120,130 model a typical impedance of a typical integrated circuit that can be coupled to the differential clock driver 110. As shown by way of example, the first load 120 includes a parallel resistor capacitor network of a capacitor CL1 in parallel with a resistor RL1. Also as shown by way of example, the second load 130 includes a parallel resistor capacitor network of a capacitor CL2 in parallel with a resistor RL2.
Referring to
The circuit 100 has a prior art differential clock driver 110 coupled to a respective load 120, 130 by respective coupling capacitors CC1, CC2 illustrated in
According to one aspect of the disclosure, there is provided a clock driver circuit with a first upper transistor and a first lower transistor that provide a first set of complementary transistors. There is a second upper transistor and a second lower transistor that provide a second set of complementary transistors. A first voltage supply node is coupled to both an electrode of the first upper transistor and an electrode of the second upper transistor, and a second voltage supply node coupled to both an electrode of the first lower transistor and an electrode of the second lower transistor. A first coupling transistor selectively couples another electrode of the first upper transistor to another electrode of the second lower transistor, and a second coupling transistor selectively couples another electrode of the second upper transistor to another electrode of the first lower transistor. There are two first series connected capacitors coupling the another electrode of the first upper transistor to the another electrode of the first lower transistor, and two second identical series connected capacitors couple the another electrode of the second upper transistor to the another electrode of the second lower transistor. An in-phase clock signal output is provided by a node intermediate the two second series connected capacitors and an anti-phase clock signal output is provided by a node intermediate the two first series connected capacitors. An in-phase clock signal input is coupled to control inputs of the first upper transistor, the first coupling transistor and the first lower transistor. Also, an anti-phase clock signal input is coupled to control inputs of the second upper transistor, the second coupling transistor and the second lower transistor.
Referring to
The clock driver circuit 300 also has a first coupling transistor TR5 selectively coupling another electrode (the drain electrode) of the first upper transistor TR1 to another electrode (the drain electrode) of the second lower transistor TR3. There is also a second coupling transistor TR6 selectively coupling another electrode (the drain electrode) of the second upper transistor TR2 to another electrode (the drain electrode) of the first lower transistor TR4. Two first series connected capacitors C1, C4 couple the drain electrode of the first upper transistor TR1 to the drain electrode of the first lower transistor TR4, and two second series connected capacitors C2, C3 couple the drain electrode of the second upper transistor TR2 to the drain electrode of the second lower transistor TR3.
The clock driver circuit 300 also comprises an anti-phase clock signal output Voutb provided by a node intermediate the two first series connected capacitors C1,C4 and an in-phase clock signal output Vout provided by a node intermediate the two second series connected capacitors C2,C3. There is an in-phase clock signal input Vclk coupled to control inputs of the first upper transistor, the first coupling transistor and the first lower transistor. There is also an anti-phase clock signal input Vclkb coupled to control inputs of the second upper transistor, the second coupling transistor and the second lower transistor. As will be apparent to a person skilled in the art, since the upper first transistor TR1 and upper second transistor TR2 are P-type field effect transistors and the lower first transistor TR4, lower second transistor TR3, the first coupling transistor TR5 and the second coupling transistor TR6 are N-type field effect transistors, then all of the abovementioned control inputs are gate electrodes.
The first voltage supply node VDD is coupled to a positive supply potential and the second voltage supply node VSS is coupled to a reference potential (typically ground reference) relative to the positive power supply VDD. In operation, a first clock signal Ck is applied to the in-phase clock signal input Vclk and second clock signal Ckb that is anti-phase to the first clock signal Ck is applied to the anti-phase clock signal input Vcklb. The two first series connected capacitors C1, C4 and the two second series connected capacitors C2, C3 all have identical capacitance values, and the two first series connected capacitors include a lower first capacitor C4 coupled to the another electrode of the first lower transistor TR4 and an upper first capacitor C1 coupled to the another electrode of the first upper transistor TR1. The two first series connected capacitors C2, C3 include a lower second capacitor C3 coupled to the another electrode of the second lower transistor TR3 and an upper second capacitor C2 coupled to the another electrode of the second upper transistor TR2.
Illustrated in
After the clock signal Ck at the clock signal input Clk has just transitioned to a logic 1 (1.8 Volts) and the anti-phase clock signal CKb has just transitioned to a logic 0 (0 Volts), then the first upper transistor TR1 is switched off, the first lower transistor TR4 is switched on and the first coupling transistor TR5 is also switched on. Also, the second upper transistor TR2 is switched on, the second lower transistor TR3 is switched off and the second coupling transistor TR6 is also switched off. As a result, the voltage at N1 stored on the upper first capacitor C1 will discharge to share its charge with lower second capacitor C3, and thus, the voltage at N1=0.9V. The voltage at N2 will charge up to the supply voltage VDD=1.8V. The voltage at N3 stored on the lower second capacitor C3 will charge to share the charge of the upper first capacitor C1, and thus, N3=N1=0.9V and voltage at N4 will discharge to ground, and thus, N4=0V.
From analysis of the above, in operation a charge on the lower first capacitor C4 ranges from the reference potential (VSS or ground) to half the positive power supply potential (VDD/2), and the charge on the upper first capacitor C1 ranges from to half the positive power supply potential (VDD/2) to the positive power supply potential (VDD). Similarly, in operation, a charge on the lower second capacitor C3 ranges from the reference potential (VSS or ground) to half the positive power supply potential (VDD/2), and the charge on the upper second capacitor C2 ranges from to half the positive power supply potential (VDD/2) to the positive power supply potential (VDD). Thus, the charging and discharging of capacitors C1, C2, C3 and C4 results in the waveforms illustrated for Vout and Voutb that range from VDD to VSS or ground.
Referring to
Advantageously, the first upper and first lower transistors TR1, TR4 are configured and biased to operate in a class AB operation so that only one transistor can be turned on at any instance, thereby eliminating the possibility of shorting the supply voltage to ground. Similarly, the second upper and second lower transistors TR2, TR3 are configured and biased to operate in a class AB operation. The present invention provides for a split level charging/discharging using capacitors C1 to C4, and thus, these capacitors maximum discharge voltage range, resulting from a clock signal transition, is VDD/2. The present invention therefore provides clock driver faster output response times at Vout and Voutb with reduced power consumption.
In the foregoing specification, specific embodiments of the present invention have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. For instance all N-type transistors of
Claims
1. A clock driver circuit comprising:
- a first upper transistor and a first lower transistor providing a first set of complementary transistors;
- a second upper transistor and a second lower transistor providing a second set of complementary transistors;
- a first voltage supply node coupled to both an electrode of the first upper transistor and an electrode of the second upper transistor;
- a second voltage supply node coupled to both an electrode of the first lower transistor and an electrode of the second lower transistor;
- a first coupling transistor selectively coupling another electrode of the first upper transistor to another electrode of the second lower transistor;
- a second coupling transistor selectively coupling another electrode of the second upper transistor to another electrode of the first lower transistor;
- two first series connected capacitors coupling the another electrode of the first upper transistor to the another electrode of the first lower transistor;
- two second identical series connected capacitors coupling the another electrode of the second upper transistor to the another electrode of the second lower transistor;
- an in-phase clock signal output provided by a node intermediate the two second series connected capacitors;
- an anti-phase clock signal output provided by a node intermediate the two first series connected capacitors;
- an in-phase clock signal input coupled to control inputs of the first upper transistor, the first coupling transistor and the first lower transistor; and
- an anti-phase clock signal input coupled to control inputs of the second upper transistor, the second coupling transistor and the second lower transistor.
2. A clock driver circuit as claimed in claim 1, wherein the upper first transistor and upper second transistor are P-type field effect transistors and wherein the lower first transistor and lower second transistor are N-type field effect transistors.
3. A clock driver circuit, as claimed in claim 2, wherein the first coupling transistor and the second coupling transistor are N-type field effect transistors.
4. A clock driver circuit, as claimed in claim 1, wherein the upper first transistor and upper second transistor are PNP bipolar transistors, and wherein the lower first transistor and lower second transistor are NPN bipolar transistors.
5. A clock driver circuit, as claimed in claim 3, wherein the first coupling transistor and the second coupling transistor are NPN bipolar transistors.
6. A clock driver circuit, as claimed in claim 1, wherein the two first series connected capacitors and the two second series connected capacitors all have identical capacitance values.
7. A clock driver circuit, as claimed in claim 1, wherein the first voltage supply node is coupled to a positive power supply potential and the second voltage supply node is coupled to a reference potential relative to the positive power supply.
8. A clock driver circuit, as claimed in claim 7, wherein in operation a first clock signal is applied to the in-phase clock signal input and second clock signal that is anti-phase to the first clock signal is applied to the anti-phase clock signal input.
9. A clock driver circuit, as claimed in claim 7, wherein the two first series connected capacitors and the two second series connected capacitors all have identical capacitance values and the two first series connected capacitors include a lower first capacitor coupled to the another electrode of the first lower transistor and an upper first capacitor coupled to the another electrode of the first upper transistor, and wherein in operation a charge on the lower first capacitor ranges from the reference potential to half the positive power supply potential and the charge on the upper first capacitor ranges from to half the positive power supply potential to the positive power supply potential.
10. A clock driver circuit, as claimed in claim 9, wherein in operation a charge on the lower second capacitor ranges from the reference potential to half the positive power supply potential and the charge on the upper second capacitor ranges from to half the positive power supply potential to the positive power supply potential.
11. A clock driver circuit, as claimed in claim 1, wherein the first upper transistor and first lower transistor are configured and biased to operate in a class AB operation.
12. A clock driver circuit, as claimed in claim 1, wherein the second upper transistor and first lower transistor are configured and biased to operate in a class AB operation.
Type: Application
Filed: Dec 20, 2008
Publication Date: Jun 24, 2010
Applicant: MOTOROLA, INC. (SCHAUMBURG, IL)
Inventor: YIN WAN OI (PENANG)
Application Number: 12/340,658