Abstract:
Some embodiments include apparatus and methods having a clock path with a combination of current-mode logic (CML) based and complementary metal-oxide semiconductor (CMOS) components.

Description:
PRIORITY APPLICATION 
     This application is a divisional of U.S. application Ser. No. 13/025,777, filed Feb. 11, 2011 now U.S. Pat. No. 8,278,993, which is a divisional of U.S. application Ser. No. 12/408,930, filed Mar. 23, 2009, now issued as U.S. Pat. No. 7,888,991, which are both incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     Many integrated circuit (IC) devices, such as processors and memory devices, often use clock signals as timing for data capture and transfer. The device may include a network to distribute clock signals from one location to other locations within the device. Clock signals in these devices are usually susceptible to variations in operating voltage and temperature, potentially causing inaccurate data capture or transfer, especially when these devices operate at high frequency, such as frequency in gigahertz range. Therefore, in some devices, designing a network to distribute clock signals may pose a challenge. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a block diagram of an IC device including a clock path, according to an embodiment of the invention. 
         FIG. 2  shows a block diagram of an IC device including a clock path having a clock distribution network (CDN), according to an embodiment of the invention. 
         FIG. 3  shows a block diagram of a portion of a clock path including a combination of current-mode logic (CML) based components and complementary metal-oxide semiconductor (CMOS) inverters, according to an embodiment of the invention. 
         FIG. 4  is a timing diagram showing clock signals having different phases and frequencies, according to an embodiment of the invention. 
         FIG. 5  shows a block diagram of a portion of a clock path with a converter located at local clock trees, according to an embodiment of the invention. 
         FIG. 6  shows a block diagram of a portion of a clock path with clock trees having different clock phases, according to an embodiment of the invention. 
         FIG. 7  shows a block diagram of a portion of a clock path with clock trees having the same components, according to an embodiment of the invention. 
         FIG. 8  shows a schematic diagram of a CML-based component, according to an embodiment of the invention. 
         FIG. 9  shows a schematic diagram of a divider circuit, according to an embodiment of the invention. 
         FIG. 10  shows a block diagram of an IC device including a bias generator, according to an embodiment of the invention. 
         FIG. 11  shows a block diagram of a bias generator with a current source having adjustable parallel current paths, according to an embodiment of the invention. 
         FIG. 12  shows a block diagram of a bias generator having multiple current sources, according to an embodiment of the invention. 
         FIG. 13  is a flow diagram of a method, according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a block diagram of an integrated circuit device  100  including a clock path  110 , according to an embodiment of the invention. IC device  100  can be a memory device or a processor. Clock path  110  of IC device  100  receives clock signals CK and CK#. The “#” designation in CK# indicates that the CK# signal is inverted with respect to the CK signal. The CK and CK# signals together form a differential signal. Thus, the CK and CK# signals can be considered as components of a differential signal. The CK and CK# signals may be external to IC device  100 . Clock path  110  includes a clock distribution network (CDN)  112  to distribute the CK and CK# signals, or signals generated from the CK and CK# signals, to various locations within IC device  100 . 
     IC device  100  also includes a data path  120  to transfer data within IC device  100  or to transfer data to and from IC device  100 . In  FIG. 1 , “DATA” presents the data transfer to and from IC device  100 . IC device  100  uses the CK and CK# signals as timing signals to transfer data, on data path  120 . Data path  120  may include components, such as data receivers, latches, and deserializers. The data receivers can be differential amplifier (e.g., sense-amp based) data receivers. Data on data path  120  includes data transferred to and from memory cells  130 . 
     IC device  100  also includes a bias generator  180  to generate a bias voltage V BIAS  based on a bandgap reference generator  170 . IC device  100  uses bias voltage V BIAS  to control gates of transistors of at least some of the components of clock path  110 . 
     Some of the components of IC device  100 , such as clock path  110  and bias generator  180 , can be similar to or identical to the components described below with reference to  FIG. 2  through  FIG. 13 . 
       FIG. 2  shows a block diagram of an IC device  200  including a clock path  210  having a CDN  212 , according to an embodiment of the invention. Clock path  210  includes a receiver  232  to receive a differential clock signal formed by clock signals CK and CK#, which can have a frequency corresponding to a frequency of a clock (e.g., system clock) of a system that includes IC device  200 . Clock path  210  uses the CK and CK# signals to generate other clock signals with different phases and different frequencies for internal data capture and transfer within IC device  200 . 
     A buffer  234  receives the CK and CK# signals and generates a 2-phase differential clock signal that includes clock signals CK 2  and CK 2 #. The CK 2  and CK 2 # signals can be generated to have the same frequency as the frequency of the CK and CK# signals. Clock path  210  may include a duty cycle correction circuit (not shown) coupled to receiver  232  and buffer  234  to improve duty cycle of the CK 2  and CK 2 # signals. 
     CDN  212  includes a receiver and divider circuit  236  to receive the CK 2  and CK 2 # signals to generate 4-phase differential clock signals including a first differential clock signal formed by clock signals CK 4   A  and CK 4   A #, and a second differential clock signal formed by clock signals CK 4   B  and CK 4   B #. The CK 4   A , CK 4   A #, CK 4   B , and CK 4   B # signals can be generated to have a frequency that is one-half of the frequency of the CK 2  and CK 2 # signals. 
     CDN  212  also includes a converter  238 , which is a current-mode logic (CML) to CMOS signal (CML-to-CMOS) converter and can include a differential to single-ended signal converter. Converter  238  converts four components (CK 4   A , CK 4   B , and CK 4   B #) of the two differential clock signals into four single-ended clock signals CK 4   0 , CK 4   90 , CK 4   180 , and CK 4   270  on lines  239  for distribution to a clock tree system  240 . 
     As shown in  FIG. 2 , clock path  210  includes a combination of both CML-based and CMOS-based components. CML-based components include receiver  232 , buffer  234 , receiver and divider circuit  236 , and converter  238 . CMOS-based components include inverter circuits  250  and local clock trees  260 . In this description, a CML-based component refers to a component having input nodes to receive input differential signals and output nodes to provide output differential signals. A CMOS-based component refers to a component having an input node to receive an input CMOS-level signaling and an output node to provide a CMOS-level signaling. A differential signal and a CMOS signal can make a transition from one signal level to another signal level. The transition can be considered a “swing” of the signal. The signal levels can include supply voltage and ground potential levels, which are usually provided through conductors that are sometimes called “rails”. The signal swing of CMOS signals generated by CMOS components are generally greater than the signal swing of differential signals received at or generated by CML-based components. For example, CMOS signals can swing from supply voltage level (e.g., Nice) to ground and vice versa (or rail to rail). Differential signals associated with CML-based components generally have signal swings that are less than rail to rail. 
     As shown in  FIG. 2 , inverter circuits  250  and local clock trees  260  are arranged in an H-tree arrangement. Inverter circuits  250  can be considered part of a global clock tree of clock tree system  240 . The global clock tree can extend a relatively long distance within IC device  200 . Local clock trees  260  can be located locally near data latches and deserializers of IC device  200 . The CK 4   0 , CK 4   90 , CK 4   180 , and CK 4   270  signals have signal levels corresponding to CMOS signal level. Clock tree system  240  distributes the CK 4   0 , CK 4   90 , CK 4   180 , and CK 4   270  signals to inverter circuits  250  and local clock trees  260  for data capture and transfer. 
     Each inverter circuit  250  includes four CMOS inverters, and each of the four inverters receives one of the CK 4   0 , CK 4   90 , CK 4   180 , and CK 4   270  signals. Each local clock tree  260  can include additional inverters (not shown) to further distribute the CK 4   0 , CK 4   90 , CK 4   180 , and CK 4   270  signals. The single lines between the individual inverter circuits  250  and local clock trees  260  include multiple lines to carry multiple clock signals.  FIG. 2  shows these multiple lines as single lines for simplicity. 
     IC device  200  also includes a bandgap reference generator  270  to generate voltage and current that are substantially constant over variations in the fabricating process, operating voltage and temperature. A bias generator  280  generates a bias voltage V BIAS  based on bandgap reference generator  270 , such as based on the voltage or current from bandgap reference generator  270 . IC device  200  uses bias voltage V BIAS  to control the gate of transistors in other components of IC device  200 , including CML-based components. 
     Some conventional clock paths may include only CMOS inverters or only CML-based components. CMOS inverters are generally more susceptible to supply voltage variation than CML-based components. CML-based components generally consume more power than CMOS-based components. Thus, some conventional clock paths may be sensitive to supply voltage variation or may consume relatively more power. In clock path  210 , however, a combination of both CML-based components and CMOS-based components can reduce power consumption, or improve sensitivity to supply voltage variation, or both. 
     CML-based components are generally sensitive to temperature. In some cases, variation in operating temperature can increase the temperature dependency of CML-based components. However, an appropriate value of a bias voltage, such as bias voltage V BIAS  of  FIG. 2 , can reduce the temperature dependency of CML-based components, such as the CML-based components in IC device  200  of  FIG. 2 . Generation of bias voltage V BIAS  is described in more detail below with reference to  FIG. 10  through  FIG. 13 . 
       FIG. 3  shows a block diagram of a portion of a clock path  310  including a combination of CML-based components and CMOS inverters, according to an embodiment of the invention. Components of clock path  310  can be used in clock path  210  of  FIG. 2 . Clock path  310  of  FIG. 3  includes additional components similar to those of clock path  210  of  FIG. 1 . However,  FIG. 3  shows only a portion of clock path  310  to focus on specific components shown therein. 
     As shown in  FIG. 3 , clock path  310  includes CML-based components, such as receiver  333  and divider  335 , and CMOS-based components such as inverters  350 . Receiver  333  receives a differential dock signal (CK 2 /CK 2 #). Divider  335  receives the CK 2  and CK 2 # signals to generate two different differential clock signals, one formed by the CK 4   A  and CK 4   A # signals and the other one formed by the CK 4   B  and CK 4   B # signals. 
     Converter  338  is a CML-to-CMOS signal converter and can include a differential to single-ended signal converter. Converter  338  converts the two differential clock signals (CK 4   A /CK 4   A # and CK 4   B /CK 4   B #) into four single-ended clock signals CK 4   0 , CK 4   90 , CK 4   180 , and CK 4   270  on lines  339 , which correspond to lines  239  of  FIG. 2 . 
     A clock tree system  340  includes four inverters  350 , each receiving a corresponding clock signal CK 4   0 , CK 4   90 , CK 4   180 , or CK 4   270 . Inverters  350  provide the CK 4   0 , CK 4   90 , CK 4   180 , and CK 4   270  signals to one or more branch of clock tree system  340  for further distribution. The CK 4   0 , CK 4   90 , CK 4   180 , and CK 4   270  signals can be used as clock signals for data latches and other components, such as deserializers, to capture and transfer data. 
       FIG. 4  is a timing diagram showing clock signals having different phases and frequencies, according to an embodiment of the invention. The clock signals shown in  FIG. 4  correspond to the same signals shown in  FIG. 1 ,  FIG. 2 , and  FIG. 3 . 
     As shown in  FIG. 4 , the CK and CK# signals have a cycle (period) “T” or a frequency f 1 =1/T. 
     The CK 2  and CK 2 # signals also have a cycle of T or a frequency f 2 =f 1 =1/T, which is equal to the frequency f 1  of the CK signal. The CK 2  and CK 2 # signals are 180 degrees (or ½ of their cycle T) relative to each other. 
     The CK 4   0 , CK 4   90 , CK 4   180 , and CK 4   270  signals have a cycle of 2T or a frequency f 4 =½T, which is one-half the frequency f 2  of the CK 2  and CK 2 # signals. The CK 4   0 , CK 4   90 , CK 4   1800 , and CK 4   270  signals are 90 degrees (or ¼ of their cycle 2T) out of phase relative to each other. 
     The data (DATA) can have a frequency f D  equal to four times the frequency f 4  of the CK 4   0 , CK 4   90 , CK 4   180 , and CK 4   270  signals (e.g., f D =4f 4 =2/T), such that during each clock cycle T, two bits of data can be captured or transferred. Data capture and transfer can occur at the edge (e.g., rising edge) of the CK 4   0 , CK 4   90 , CK 4   180 , and CK 4   270  signals. For example, as shown in  FIG. 4 , four data bits B 0 , B 1 , B 2 , and B 3  of the data (DATA) can be captured or can be deserialized using four consecutive rising edges of the CK 4   0 , CK 4   90 , CK 4   180 , and CK 4   270  signals. 
       FIG. 5  shows a block diagram of a portion of a clock path  510  with a converter  538  located at local clock trees  560 , according to an embodiment of the invention. Clock path  510  includes a combination of CML-based components, such as CML receiver  533 , CML divider  535 , CML buffers  550 , and CMOS-based components, such as CMOS inverter  555 .  FIG. 5  shows details of components within only one local clock tree  560  for clarity. Local clock trees  560 , however, have similar components. 
     Clock path  510  can be considered a variation of clock path  210  of  FIG. 2 , with CML buffers  550  in  FIG. 5  replacing CMOS inverter circuits  250  of  FIG. 2  and converter  538  of  FIG. 5  located at local clock trees  560 . In  FIG. 2 , converter  238  is located outside local clock trees  260  and converts differential signals CK 4   A /CK 4   A # and CK 4   B /CK 4   B # into 4-phase CMOS clock signals (CK 4   0 , CK 4   90 , CK 180 , and CK 4   270 ). Then, clock path  210  distributes the 4-phase CMOS clock signals to local clock trees  260 . In  FIG. 5 , however, differential signals CK 4   A /CK 4   A # and CK 4   B /CK 4   B # are distributed to local clock trees  260  by CML buffers  550 . Then, converter  538  locally converts differential signals CK 4   A /CK 4   A # and CK 4   B /CK 4   B # into the 4-phase CMOS clock signals (e.g., CK 4   0 , CK 4   90 , CK 4   180 , and CK 4   270 ). 
       FIG. 6  shows a block diagram of a portion of a clock path  610  with clock trees  641  and  642  having different clock phases, according to an embodiment of the invention. Clock path  610  includes receivers  633  to receive a differential signal, formed by clock signals CK 2  and CK 2 #, and sends it to clock trees  641  and  642 . The CK 2  and CK 2 # signals are 2-phase clock signals that clock tree  641  uses as timing signal to capture data (DATA) at latches  621 . Clock tree  642  includes a divider  634  and inverter circuit  636  to convert the 2-phase clock signals CK 2  and CK 2 # into 4-phase clock signals CK 4   0 , CK 4   90 , CK 4   180 , and CK 4   270  on lines  639 . Clock tree  642  uses the CK 4   0 , CK 4   90 , CK 4   180 , and CK 4   270  signals to deserialize data at deserializer  622  before the data is stored, for example, in memory cells. 
       FIG. 7  shows a block diagram of a portion of a clock path  710  with clock trees  741  and  742  having the same components, according to an embodiment of the invention. Clock path  710  receives a differential clock signal, formed by clock signals CK 2  and CK 2 #, at receiver  733  and sends it to clock trees  741  and  742  via CML buffers  734 . Each of clock trees  741  and  742  includes a divider  735 , a converter  738 , and a CMOS inverter circuit  750  to receive the CK 2  and CK 2 # signals to generate 4-phase CMOS clock signals CK 4   0 , CK 4   90 , CK 4   180 , and CK 4   270  to capture data (DATA) at data latches  721  or  722 . 
       FIG. 8  shows a schematic diagram of a CML-based component  800 , according to an embodiment of the invention. CML-based component  800  has a differential amplifier configuration with a load  802  and a constant current I. CML-based component  800  includes transistors  803  and  804  to receive a differential clock signal, formed by clock signals CK IN  and CK IN #, and generate a differential clock signal, formed by clock signals CK OUT  and CK OUT #. CML-based component  800  also includes a transistor  805  having a gate controlled by an enable signal EN to activate or deactivate CML-based component  800 . CML-based component  800  further includes a transistor  806  having a gate controlled by a bias voltage V BIAS . A bias generator, similar to bias generator  280  of  FIG. 1 , provides bias voltage V BIAS . CML-based component  800  with the different amplifier configuration show in  FIG. 8  (or with other different amplifier configurations) can be used as receiver  232  of  FIG. 2 , receiver  333  of  FIG. 3 , CML buffers  550  of  FIG. 5 , receivers  633  of  FIG. 6 , CML buffer  637  of  FIG. 6 , and CML buffers  734  of  FIG. 7 .  FIG. 8  shows an example of a differential amplifier configuration of CML-based component  800 . CML-based component  800 , however, can include other differential amplifier configurations. 
       FIG. 9  shows a schematic diagram of a divider circuit  935 , according to an embodiment of the invention. Divider circuit  935  can be used as the divider circuits described above, such as divider  335  of  FIG. 3 . In  FIG. 9 , divider circuit  935  is a CML latch-based divider circuit with CML latches  911 ,  912 ,  921 , and  922 . The circuit components, such as transistors N 1  through N 7  and resistors R 1  and R 2  of CML latches  911 ,  912 ,  921 , and  922  are similar and are arranged in similar ways as shown in  FIG. 9 . For clarity,  FIG. 9  omits details of CML latches  911  and  921 . 
     CML latches  911  and  912  form two stages (e.g., master and slave stages) of a first divider to receive a different clock signal that includes clock signals CK 2  and CK 2 # and generate a differential signal that includes clock signals CK 4   A  and CK 4   A #. As shown in  FIG. 9 , the gates of two transistors N 1  and N 2  of CML latch  912  are controlled by clock signals CK 2  and CK 2 #, and the gate of a transistor N 3  is controlled by a bias voltage V BIAS . A bias generator, which can be similar to bias generator  280  of  FIG. 2 , provides bias voltage V BIAS . The CK 4   4  and CK 4   4 # signals generated by latches  911  and  912  have a frequency equal to one-half of the frequency of the CK 2  and CK 2 # signals. 
     CML latches  921  and  922  form two stages (e.g., master and slave) of a second divider to receive the same CK 2  and CK 2 # signals and generate a differential signal that includes clock signals CK 4   B  and CK 4   B #. CML latches  921  and  922  operate in ways similar to those of CML latches  911  and  912 , except that the CK 2  and CK 2 # signals are swapped at gates of transistors N 1  and N 2  of CML latches  921  and  922 . Transistor N 3  of CML latch  922  is controlled by the same bias voltage V BIAS . 
     Divider circuit  935  may provide the CK 4   A , CK 4   A #, CK 4   B , CK 4   B # signals to a converter, such as converter of  238  of  FIG. 2  or converter  338  of  FIG. 3 , to generate 4-phase CMOS clock signals, such as the CK 4   0 , CK 4   90 , CK 4   180 , and CK 4   270  clock signals of  FIG. 2  and  FIG. 3 . 
       FIG. 10  shows a block diagram of an IC device  1000  including a bias generator  1080 , according to an embodiment of the invention. IC device  1000  may include components similar to or identical to those of device  100  of  FIG. 1  and IC device  200  of  FIG. 2 .  FIG. 10  shows only a portion of IC device  1000  to focus on bias generator  1080  and bandgap reference generator  1070 . 
     Bias generator  1080  generates a bias voltage V BIAS , which can be used as bias voltage V BIAS  described above with reference to  FIG. 1  through  FIG. 9 . 
     As shown in  FIG. 10 , bias generator  1080  includes generator portions  1010  and  1020  to generate voltages V INIT  and V ADJ  based on a current I REF  from bandgap reference generator  1070 . Current I REF  is a bandgap reference current that is substantially constant over variations in operating voltage and temperature. Bias generator  1080  includes a calibrating process to adjust the value of voltage V ADJ  based on the relationship between voltages V INIT  and V ADJ  during the calibrating process. After the value of voltage V ADJ  is adjusted to a selected value, bias generator  1080  stops the calibrating process to maintain the value of bias voltage V BIAS . As shown in  FIG. 10 , bias generator  1080  includes a unity gain amplifier  1050  to provide voltage bias V BIAS , which is equal to voltage V ADJ . Unity gain amplifier  1050  can act as a filter to improve signal characteristic of bias voltage V BIAS . 
     Generator portion  1010  includes a current source  1012  and a load formed by transistors  1014  and  1016  that are coupled as a diode load and in series with current source  1012  on a circuit path between nodes  1098  and  1099 . Node  1098  can include a supply node having a supply voltage Vcc, Node  1099  can include a ground potential. Current source  1012  may include a current mirror to generate current I INIT  based on current I REF , such that current I INIT  can be equal to current I REF , As shown in  FIG. 10 , voltage V INIT  is a function of current I INIT  and a resistance across the diode load formed by transistors  1014  and  1016 . 
     Generator portion  1020  includes a current source  1022  and a load, formed by a resistor R, coupled in series with current source  1022  on a circuit path between nodes  1098  and  1099 . Current source  1022  may include a current mirror to generate current I ADJ  based on current I REF . Current I ADJ  is an adjustable current. It can be adjusted using a code (represented by “CODE” in  FIG. 10 ), The CODE can be a digital code having one or more bits.  FIG. 11  and  FIG. 12  (described below) show examples of an adjustable current source that can be used for current source  1022  of  FIG. 10 , As shown in  FIG. 10 , voltage V ADJ  is a function of current I ADJ  and the resistance of resistor R. Thus, the value of voltage V ADJ  can be adjusted by adjusting the value of current I ADJ . Further, since bias voltage V BIAS  is generated based on voltage V ADJ , bias voltage V BIAS  is also a function of current I ADJ  and the resistance of resistor R. 
     As described above, bias generator  1080  includes calibrating process to adjust the value of bias voltage V BIAS  based on the relationship between voltages V INIT  and V ADJ . In  FIG. 10 , during a calibrating process, a comparator  1030  compares the value of voltage V ADJ  with the value of voltage V INIT  and adjusts the value of voltage V ADJ  based on the results of the comparison. The value of current I INIT  and voltage are not adjusted during the calibrating process. Thus, the value of voltage V INIT  can be used as a target value during the calibrating process. 
     Current source  1022  can be set such that the value of voltage V ADJ  is set to a starting value within a voltage range (described below) and less than the value of voltage V INIT  at the beginning of the calibrating process. Then, based on the comparison during a calibrating process, a controller  1040  changes the value of the CODE to change the value of current I ADJ  and increase the value of voltage V ADJ . The adjustment can repeat until the value of voltage V ADJ  is at least equal to the value of voltage V INIT . Controller  1040  may include a digital counter to set the value of the CODE corresponding to a count value of the counter. Controller  1040  may use the counter to count up, increasing the value of the count value, which can correspond to an increase in the value of current I ADJ . 
     Current source  1022  can be alternatively set such that the value of voltage V ADJ  is set to a starting value within a value range and greater than (instead of less than, as described above) the value of voltage V INIT  at the beginning of the calibrating process, Then, based on the comparison during a calibrating process, controller  1040  can change the value of the CODE to change the value of current I ADJ  and decrease the value of voltage V ADJ . In the alternative way, controller  1040  may use a counter to count down, decreasing the value of the count value, which can correspond to a decrement in the value of current I ADJ . The adjustment can repeat until the value of voltage I ADJ  is at most equal to the value of voltage V INIT . 
     The voltage range of voltage V ADJ  (mentioned above) can be determined by measuring its values (e.g., during design) for different process variations. Thus, the voltage range is known before the value of voltage V ADJ  is set. The voltage range of voltage V INIT  can also be determined by measuring its values for different process corners. Based on the voltage ranges, the starting value of V ADJ  at the beginning of the calibrating process can be set to a value within its voltage range (e.g., a lowest value in the voltage range and less than or greater than the value of voltage V INIT . 
     Bias generator  1080  may perform the calibrating process only one time, for example, only during a power-up sequence of IC device  1000 . After the calibrating process, for example, after the power-up sequence, IC device  1000  may switch one or more of generator portion  1010 , comparator  1030 , and controller  1040  to a lower power mode to save power. Such lower power mode may include an idle mode or an off mode. 
     IC device  1000  includes an operating temperature range with a first operating temperature limit lower than a second operating temperature limit. Bias generator  1080  may perform the calibrating process to adjust voltage V ADJ  at a temperature that is closer to the first operating temperature limit than the second operating temperature limit. For example, IC device  1000  may have an operating temperature range from 0° C. to 100° C. and bias generator  1080  may perform the calibrating process at 25° C., Performing the calibrating process at a relatively lower temperature within operating temperature range may improve performance of device  100 . 
       FIG. 11  shows a block diagram of a bias generator  1180  with a current source  1122  having adjustable parallel current paths  1100 ,  1101 , and  1102 , according to an embodiment of the invention. Bias generator  1180  can correspond to bias generator  1080  of  FIG. 10 ,  FIG. 11  shows only a portion of generator  1180  to focus on current source  1122 , which can correspond to current source  1022  of  FIG. 10 . In  FIG. 11 , bias generator  1180  generates a voltage V ADJ , which can be used to generate a bias voltage (e.g., V BIAS =V ADJ ) similar to or identical to bias voltage V BIAS  in  FIG. 10 . In  FIG. 11 , voltage V ADJ  has a value based on the value of a current I ADJ  and the resistance of a resistor R. The value of current I ADJ  can be generated based on bandgap reference generator  1170 . 
     As shown in  FIG. 11 , bandgap reference generator  1170  includes a bandgap internal circuitry  1171 , transistors P 0 , and a resistor R REF  to generate a bandgap current I REF . Current source  1122  includes transistors P 1  through P 9  arranged in a current mirror configuration with transistors P 0  to generate a current I ADJ  based on current I REF . The value of the current I ADJ  is equal to a sum of the values of currents on current paths  1100 ,  1101 , and  1102 . Each of these current paths can be configured to have different current values. For example, transistors P 1  through P 9  can have different sizes so that currents on current paths  1100 ,  1101 , and  1102  can have different values. 
     Bias generator  1180  receives a code having bits C 0 , C 1 , and C 2  to select a combination of current paths  1100 ,  1101 , and  1102 .  FIG. 11  shows current source  1122  having only three current paths  1100 ,  1101 , and  1102  as an example. The number of current paths can vary, The values of bits C 0 , C 1 , and C 2  can be controlled by a controller, such as controller  1040  of  FIG. 10 . Depending on which combination of current paths  1100 ,  1101 , and  1102  is selected, the value of current I ADJ  is increased or decreased to adjust the value of voltage V ADJ . 
     Bias generator  1180  may adjust voltage V ADJ  during a calibrating process similar to or identical to the calibrating process described above with reference to  FIG. 10 . For example, bias generator  1180  can adjust voltage V ADJ  by changing the values of bits C 0 , C 1 , and C 2  during a calibrating process. 
       FIG. 12  shows a block diagram of a bias generator  1280  having multiple current sources  1220 ,  1221 , and  1222 , according to an embodiment of the invention. Bias generator  1280  can correspond to bias generator  1080  of  FIG. 10 .  FIG. 12  shows only a portion of generator  1280  to focus on current sources  1220 ,  1221 , and  1222 . Bias generator  1280  generates a voltage V ADJ , which can be used to generate a bias voltage (e.g., V BIAS =V ADJ ) similar to or identical to bias voltage V BIAS  in  FIG. 10 . In  FIG. 12 , voltage V ADJ  has a value based on the value of a current I ADJ  and the resistance of a resistor R. The value of current I ADJ  can be generated based on a bandgap current I REF  from bandgap reference generator  1270 . 
     Each of current sources  1220 ,  1221 , and  1222  can include multiple parallel current paths similar to the parallel current paths of current source  1122  of  FIG. 11 . Bias generator  1280  receives a code (represented by “CODE” in  FIG. 12 ) to control the current on each of current sources  1220 ,  1221 , and  1222 . The value of current I ADJ  is equal to the sum of current from current sources  1220 ,  1221 , and  1222 . Multiple current sources  1220 ,  1221 , and  1222  provide bias generator  1280  with more combination of current paths to select, so that current I ADJ  can be adjusted with a finer resolution and a wider range of current value. 
       FIG. 13  is a flow diagram of a method  1300 , according to an embodiment of the invention. Method  1300  can be used to generate a bias voltage and clock signals in an IC device. 
     Method  1300  includes activity  1310  to enable a bandgap reference generator. After the bandgap reference generator is settled, activity  1320  performs a calibrating process to select a value of a voltage (e.g., V ADJ ) generated based on the bandgap reference generator. The calibrating process in activity  1320  may include activities and operations of a bias generator, such as bias generators  1080 ,  1180 , and  1280  of  FIG. 10 ,  FIG. 11 , and  FIG. 12 , respectively. After the calibrating process, method  1300  continues with activity  1330  to provide the bias voltage, which is based on the voltage generated during the calibrating process. The bias voltage can be similar to or identical to bias voltage V BIAS  described above with reference to  FIG. 1  through  FIG. 12 . Activity  1330  in  FIG. 13  may perform the calibrating process only one time, for example, only during a power-up sequence of the IC device. 
     Method  1300  also includes activity  1340  to generate clock signals for data capture and transfer. Method  1300  may use the bias voltage provided by activity  1330  to control transistors of CML-based components that method  1300  uses to generate the clock signals. Generation of the clock signals in activity  1330  may include activities and operations described above with reference to  FIG. 1  through  FIG. 9  to generate clock signals, such as CK 2 , CK 2 #, CK 4   A , CK 4   A ™, CKA B , CK 4   B #, CK 4   0 , CK 4   90 , CK 4   180 , and CK 4   270 . 
     One or more embodiments described herein include apparatus and methods having a clock path with a combination of current-mode logic (CML) based and CMOS components. The apparatus and methods further include a bias generator to generate a bias voltage for use in some of the components of the clock path. Other embodiments, including additional methods and devices, are described above with reference to  FIG. 1  through  FIG. 13 . 
     The illustrations of apparatus such as IC devices  100 ,  200 , and  1000  are intended to provide a general understanding of the structure of various embodiments and not a complete description of all the elements and features of the apparatus that might make use of the structures described herein. 
     The apparatus of various embodiments includes or can be included in electronic circuitry used in high-speed computers, communication and signal processing circuitry, memory modules, portable memory storage devices (e.g., thumb drives), single or multi-processor modules, single or multiple embedded processors, multi-core processors, data switches, and application-specific modules including multilayer, multi-chip modules. Such apparatus may further be included as sub-components within a variety of electronic systems, such as televisions, memory cellular telephones, personal computers (e.g., laptop computers, desktop computers, handheld computers, tablet computers, etc.), workstations, radios, video players, audio players (e.g., MP3 (Motion Picture Experts Group, Audio Layer 3) players), vehicles, medical devices (e.g., heart monitor, blood pressure monitor, etc.), set top boxes, and others. 
     The above description and the drawings illustrate some embodiments of the invention to enable those skilled in the art to practice the embodiments of the invention. Other embodiments may incorporate structural, logical, electrical, process, and other changes. In the drawings, like features or like numerals describe substantially similar features throughout the several views. Portions and features of some embodiments may be included in, or, substituted for, those of others. Many other embodiments will be apparent to those of skill in the art upon reading and understanding the above description. For example, the embodiments described above may also apply to a CML/CMOS CDN that uses two-phase clock signals (e.g., CK and CK# or CK 2  and CK 2 #) to capture and transfer data. In the two-phase CML/CMOS CDN, a divider (e.g., CLM divider  535  of  FIG. 5 ) can be omitted. 
     The Abstract is provided to comply with 37 C.F.R. §1.72(b) requiring an abstract that will allow the reader to quickly ascertain the nature and gist of the technical disclosure. The Abstract is submitted with the understanding that it will not be used to interpret or limit the claims.