WO2007070044A1

WO2007070044A1 - Signal receiving device for receiving signals of multiple signal standards

Info

Publication number: WO2007070044A1
Application number: PCT/US2005/045281
Authority: WO
Inventors: Michael Anthony Pugel; Daniel Mark Hutchinson
Original assignee: Thomson Licensing
Priority date: 2005-12-14
Filing date: 2005-12-14
Publication date: 2007-06-21

Abstract

A signal receiving device (100, 200) such as a television signal receiver is capable of receiving signals of various different signal standards including both analog and digital signal standards. According to an exemplary embodiment, the signal receiving device (100, 200) includes a plurality of gain controllable amplifiers (20, 30) which may be connected serially. A controller (55) controls the gain of a first one of the amplifiers (20). A mode switch (60 or 70) controls the gain of the first amplifier (20) for each of the signal standards responsive to a control signal from the controller (55).

Description

TITLE

SIGNAL RECEIVING DEVICE FOR RECEIVING SIGNALS OF MULTIPLE SIGNAL

STANDARDS

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention generally relates to signal receiving devices such as television signal receivers, and more particularly, to a signal receiving device capable of receiving signals of various different signal standards including both analog and digital signal standards.

Background Information

Signal receiving devices may be capable of receiving signals of various different signal standards and/or formats. For example, devices such as television signal receivers may be capable of receiving signals of both analog signal standards (e.g., NTSC, PAL, SECAM, etc.) and digital signal standards (e.g., ATSC, QAM, QPSK, etc.). In order to accommodate these multiple signal standards, such devices may encounter performance limitations based on the operation of their automatic gain control (AGC) system.

Whether receiving signals of an analog signal standard or of a digital signal standard, the AGC system's function is to optimize the trade-off between signal-to- noise ratio (SNR) and distortion. The system SNR required to produce a noise-free picture is much higher for signals of an analog signal standard than for signals of a digital signal standard; however, signal distortion must be much lower for signals of an digital signal standard than for signals of a analog signal standard. There are several types of signal distortion of concern, all of which originate from amplifier characteristics and the signal levels being processed by those amplifiers. A particularly troublesome distortion in a system receiving digital signals is due to the presence of adjacent channel signals of either analog or digital signal standards. To quantify the distortion producing characteristics , of an amplifier, a third order distortion characteristic is often used as a figure of merit, where higher distortion performance is obtained with less third order distortion. Therefore, the optimum AGC characteristics for signals of an analog signal standard will differ considerably from those for signals of a digital signal standard.

Heretofore, signal receiving devices such as television signal receivers have failed to provide an AGC system that adequately supports both analog and digital signal standards and is able to handle a wide range of input signal levels. Accordingly, there is a need for a signal receiving device that addresses the foregoing problems. The present invention addresses these and/or other issues.

SUMMARY OF THE INVENTION

In accordance with an aspect of the present invention, a device capable of receiving a plurality of signals in which each of the signals includes information in accordance with a respective signal standard is disclosed. According to an exemplary embodiment, the device comprises a plurality of gain controllable amplifiers which may be connected serially. A controller controls the gain of a first one of the amplifiers. A mode switch controls the gain of the first amplifier for each of the signal standards responsive to a control signal from the controller.

In accordance with another aspect of the present invention, a method for providing gain control for a signal receiving device is disclosed. According to an exemplary embodiment, the method comprises steps of providing a plurality of gain controllable amplifiers which may be connected serially, providing a controller to control the gain of a first one of the amplifiers, and providing a mode switch to control the gain of said first amplifier for each of the signal standards responsive to a control signal from the controller. In accordance with another aspect of the present invention, a television signal receiver capable of receiving a plurality of signals in which each of the signals includes information in accordance with a respective signal standard is disclosed. According to an exemplary embodiment, the television signal receiver comprises a plurality of gain controllable amplifying means which may be connected serially. A control means controls the gain of a first one of the amplifying means and a switching means controls the gain of the first amplifying means for each of the signal standards responsive to a control signal from the control means.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: FIG. 1 is a block diagram of a signal receiving device according to an exemplary embodiment of the present invention;

FIG. 2 is a block diagram of a signal receiving device according to another exemplary embodiment of the present invention; and

FIG. 3 is a flowchart illustrating steps according to an exemplary embodiment of the present invention.

The exemplifications set out herein illustrate preferred embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, and more particularly to FIG. 1 , a signal receiving device 100 according to an exemplary embodiment of the present invention is shown. As indicated in FIG. 1 , signal receiving device 100 comprises tuning means such as tuner 10, first filtering means such as surface acoustic wave (SAW) filter 15, first amplifying means such as amplifier 20, second filtering means such as SAW filter 25, second amplifying means such as amplifier 30, analog-to- digital (A/D) conversion means such as A/D converter 35, processing means such as processor 40, detecting means such as AGC detector 45, digital-to-analog (D/A) conversion means such as D/A converter 50, control means such as controller 55, and switching means such as mode switch 60.

The foregoing elements of signal receiving device 100 may be implemented using integrated circuits (ICs), and one or more elements may be included on a given IC. Moreover, a given element may be included on more than one IC. For clarity of description, certain conventional elements associated with signal receiving device 100 such as certain control signals, power signals and/or other elements may not be shown in FIG. 1. According to an exemplary embodiment, signal receiving device 100 of FIG. 1 represents a portion of a television signal receiver capable of receiving signals of various different signal standards including both analog and digital modulation formats. In practice, however, signal receiving device 100 may be implemented as any type of signal receiving device capable of receiving signals of different signal standards.

Tuner 10 performs a signal tuning function. According to an exemplary embodiment, tuner 10 receives a radio frequency (RF) signal from a signal source such as a terrestrial, cable, satellite, internet and/or other signal source, and performs the signal tuning function by filtering and frequency down converting (i.e., single or multiple stage down conversion) the RF signal to thereby generate an intermediate frequency (IF) signal. The RF and IF signals may include audio, video and/or data content, and may be of an analog signal standard (e.g., NTSC, PAL,

SECAM, etc.) and/or a digital signal standard (e.g., ATSC, QAM, QPSK, etc.). Also according to an exemplary embodiment, tuner 10 receives an analog RF AGC signal from D/A converter 50 which enables an RF AGC function. SAW filter 15 filters the IF signal provided from tuner 10 to thereby generate a first filtered IF signal (e.g., as differential signals). According to an exemplary embodiment, SAW filter 15 includes one or more individual SAW filters which remove a substantial portion of the undesired, adjacent channel energy from the IF signal provided from tuner 10 to generate the first filtered IF signal. According to this exemplary embodiment, SAW filter 15 provides approximately 20 dB of signal loss through its filtering functions.

Amplifier 20 amplifies the first filtered IF signal provided from SAW filter 15 to thereby generate a first amplified IF signal. According to an exemplary embodiment, amplifier 20 of FIG. 1 amplifies the first filtered IF signal responsive to a gain control signal provided from mode switch 60. As will be described later herein, mode switch

60 controls the gain of amplifier 20 based on whether the currently received signal is of an analog signal standard or a digital signal standard. According to this exemplary embodiment, amplifier 20 provides a maximum gain of approximately 30 dB, and a noise figure of approximately 5 to 7 dB. Amplifier 20 may for example provide a 15 dB gain reduction from its maximum gain for signals of a digital signal standard.

SAW filter 25 filters the first amplified IF signal provided from amplifier 20 to thereby generate a second filtered IF signal (e.g., as differential signals). According to an exemplary embodiment, SAW filter 25 includes one or more individual SAW filters which remove a substantial portion of the undesired, adjacent channel energy from the first amplified IF signal provided from amplifier 20 to generate the second filtered IF signal. According to this exemplary embodiment, SAW filter 25 provides approximately 25 dB of signal loss through its filtering functions, and may be configured to provide different signal shaping for signals of an analog signal standard versus signals of a digital signal standard. Amplifier 30 amplifies the second filtered IF signal provided from SAW filter 25 to thereby generate a second amplified IF signal. According to an exemplary embodiment, amplifier 30 amplifies the second filtered IF signal responsive to an analog IF AGC signal provided from D/A converter 50. According to this exemplary embodiment, amplifier 30 provides a maximum gain of approximately 55 dB with a 45 dB gain reduction capability, and a noise figure of approximately 4 to 5 dB.

A/D converter 35 converts the second amplified IF signal provided from amplifier 30 from an analog format to a digital format to thereby generate a digital IF signal which represents a digital version of the second amplified IF signal provided from amplifier 30.

Processor 40 performs various digital processing functions. According to an exemplary embodiment, processor 40 performs a demodulation function, and is capable of demodulating signals of various different signal standards including analog signal standards (e.g., NTSC, PAL, SECAM, etc.) and digital signal standards (e.g., ATSC, QAM, QPSK, etc.). Once processor 40 determines proper demodulation of the digital IF signal provided from A/D converter 35, it provides an output signal to controller 55 that indicates the particular signal standard associated with that digital IF signal. Processor 40 may also be operative to perform other processing functions. As indicated in FIG. 1, output signals from processor 40 may be provided for further processing.

AGC detector 45 performs an AGC detection function. According to an exemplary embodiment, AGC detector 45 detects the magnitude of the digital IF signal output from A/D converter 35, and generates digital RF and IF AGC signals responsive to the detected magnitude.

D/A converter 50 converts the digital RF and IF AGC signals provided from AGC detector 45 from a digital format to an analog format to thereby generate analog RF and IF AGC signals. According to an exemplary embodiment, D/A converter 50 provides the analog RF AGC signal to tuner 10, and provides the analog IF AGC signal to amplifier 30 and mode switch 60.

Controller 55 performs various control functions. According to an exemplary embodiment, controller 55 receives the output signal from processor 40 that indicates the particular signal standard associated with the digital IF signal provided from A/D converter 35. In this manner, controller 55 can determine the particular signal standard associated with a currently received signal. According to another exemplary embodiment, controller 55 may determine the particular signal standard associated with a currently received signal independently of the output signal from processor 40. For example, controller 55 may include a memory, or access to a memory (not shown in FIG. 1 ), which stores data indicating which channels correspond to which signal standards. In this manner, controller 55 can determine the particular signal standard associated with a currently received signal responsive to a user channel selection input. Regardless of the technique employed, controller 55 provides a control signal to mode switch 60 that indicates the particular signal standard associated with the currently received signal. Controller 55 may also provide control signals to tuner 10 that change the RF AGC threshold (i.e., the output level of tuner 10 where RF gain reduction begins) based on the particular signal standard associated with the currently received signal. Controller 55 also provides control signals to tuner 10 responsive to user channel selection inputs to thereby effectuate a channel change function.

Mode switch 60 controls the gain of amplifier 20 based on the signal standard associated with the currently received signal. According to an exemplary embodiment, mode switch 60 provides a gain control signal to amplifier 20 responsive to the control signal from controller 55 that indicates the particular signal standard associated with the currently received signal. According to this exemplary embodiment, mode switch 60 provides a fixed voltage signal to amplifier 20 as the gain control signal when the currently received signal is of an analog signal standard (e.g., NTSC, PAL₁ SECAM, etc.). This fixed voltage signal may for example correspond to a voltage level that causes amplifier 20 to apply its maximum gain when generating the first amplified IF signal, and thereby improve the system SNR.

Also according to this exemplary embodiment, mode switch 60 provides the analog IF AGC signal (direct or scaled) from D/A converter 50 to amplifier 20 as the gain control signal when the currently received signal is of a digital signal standard (e.g., ATSC, QAM, QPSK, etc.). Using the analog IF AGC signal from D/A converter 50 as the gain control signal for amplifier 20 improves signal handling in the presence of strong signals, especially undesired adjacent channels, by reducing the incidence of amplifier distortion. The number of different voltage levels provided by mode switch 60 for the gain control signal to amplifier 20 is a matter of design choice. For example, mode switch 60 may use a different voltage level for the gain control signal to amplifier 20 for each individual signal standard that signal receiving device 100 is capable of receiving.

Referring now to FIG. 2, a signal receiving device 200 according to another exemplary embodiment of the present invention is shown. Signal receiving device 200 of FIG. 2 includes many of the same elements as signal receiving device 100 of FIG. 1 , and like reference numbers are used to represent the same or similar elements. For clarity of description, these common elements will not be described again. In addition to these common elements, signal receiving device 200 of FIG. 2 further includes and second detecting means such as AGC detector 65 and switching means such as mode switch 70 (instead of mode switch 60).

The elements of signal receiving device 200 may also be implemented using

ICs, and one or more elements may be included on a given IC. Moreover, a given element may be included on more than one IC. For clarity of description, certain conventional elements associated with signal receiving device 200 such as certain control signals, power signals and/or other elements may not be shown in FIG. 2. According to an exemplary embodiment, signal receiving device 200 of FIG. 2 also represents a portion of a television signal receiver capable of receiving signals of various different signal standards including both analog and digital modulation formats, but may be implemented as any type of signal receiving device capable of receiving signals of different signal standards.

AGC detector 65 performs an AGC detection function for amplifier 20. According to an exemplary embodiment, AGC detector 65 detects the magnitude of the first amplified IF signal output from amplifier 20, and generates a second IF AGC signal responsive to the detected magnitude that is used to control the gain of amplifier 20. In this manner, AGC detector 65 is dedicated to performing the AGC detection and control functions for amplifier 20. Also according to an exemplary embodiment, AGC detector 65 receives a control signal from mode switch 70 that may adjust its IF AGC threshold (i.e., the output level of amplifier 20 at which AGC detector 65 begins IF gain reduction). As will be described later herein, AGC detector 65 adjusts its IF AGC threshold responsive to the control signal from mode switch 70 for each individual signal standard that signal receiving device 200 is capable of receiving, and thereby optimizes its signal receiving capabilities.

Mode switch 70 controls the gain of amplifier 20 via AGC detector 65 based on the signal standard associated with the currently received signal. According to an exemplary embodiment, mode switch 70 receives a control signal from controller 55 that indicates the particular signal standard associated with the currently received signal, and provides a corresponding control signal to AGC detector 65 responsive to the control signal from controller 55. The control signal from mode switch 70 controls the IF AGC threshold of AGC detector 65 by indicating the output level of amplifier 20 at which AGC detector 65 begins IF gain reduction. In this manner, AGC detector 65 uses an IF AGC threshold most suitable for the particular signal standard associated with the currently received signal. According to an exemplary embodiment, the control signal from mode switch 70 to AGC detector 65 may be used to establish at least three different IF AGC thresholds. For example, a first IF AGC threshold may be used to optimize the system SNR, which may be advantageous for certain analog signal standards such as NTSC. A second IF AGC threshold may for example be used to provide a lower system SNR than is needed for certain analog signal standards such as NTSC, but better than what is needed for certain digital signal standards such as ATSC. This second IF AGC threshold may for example be advantageous for digital signal standards such as QAM. A third IF AGC threshold may also be used to reduce signal distortion and optimize signal level handling capability, particularly in the presence of strong undesired adjacent channels. This third IF AGC threshold may for example be advantageous for digital signal standards such as ATSC. Other IF AGC thresholds may also be used for other signal standards according to principles of the present invention.

Referring now to FIG. 3, a flowchart 300 illustrating steps according to an exemplary embodiment of the present invention is shown. In particular, the steps of FIG. 3 represent a signal processing technique using AGC according to principles of the present invention. For purposes of example and explanation, the steps of FIG. 3 will be described with reference to signal receiving device 100 of FIG. 1. However, the steps of FIG. 3 could also be performed using signal receiving device 200 of FIG. 2. Accordingly, the steps of FIG. 3 are exemplary only, and are not intended to limit the present invention in any manner.

At step 310, signal receiving device 100 tunes an RF signal and thereby generates a resultant IF signal. According to an exemplary embodiment, tuner 10 receives the RF signal from a signal source such as a terrestrial, cable, satellite, internet and/or other signal source and performs a signal tuning function by filtering and frequency down converting (i.e., single or multiple stage down conversion) the RF signal to thereby generate the IF signal at step 310. The RF and IF signals may include audio, video and/or data content, and may be of an analog signal standard (e.g., NTSC, PAL, SECAM, etc.) and/or a digital signal standard (e.g., ATSC, QAM, QPSK, etc.). Also according to an exemplary embodiment, tuner 10 performs the signal gain control function at step 310 responsive to the analog RF AGC signal provided from D/A converter 50.

At step 320, signal receiving device 100 processes the IF signal generated at step 310 to thereby generate a digital IF signal. According to an exemplary embodiment, the digital IF signal is generated at step 320 via the processing functions of SAW filter 15, amplifier 20, SAW filter 25, amplifier 30, and A/D converter 35 in the following manner. First, SAW filter 15 removes a substantial portion of the undesired, adjacent channel energy from the IF signal provided from tuner 10 to thereby generate a filtered IF signal (e.g., as differential signals). Next, amplifier 20 amplifies the filtered IF signal responsive to a gain control signal provided from mode switch 60 to thereby generate a first amplified IF signal. SAW filter 25 then filters the first amplified IF signal to thereby generate a second filtered IF signal (e.g., as differential signals). Amplifier 30 then amplifies the second filtered IF signal responsive to an analog IF AGC signal from D/A converter 50 to thereby generate a second amplified IF signal. Finally, A/D converter 35 converts the second amplified IF signal provided from amplifier 30 from an analog format to a digital format to thereby generate the digital IF signal at step 320.

At step 330, signal receiving device 100 detects the magnitude of the digital IF signal generated at step 320. According to an exemplary embodiment, AGC detector 45 detects the magnitude of the digital IF signal output from A/D converter 35, and generates digital RF and IF AGC signals responsive to the detected magnitude. D/A converter 50 then converts the digital RF and IF AGC signals from a digital format to an analog format to thereby generate analog RF and IF AGC signals. D/A converter 50 provides the analog RF AGC signal to tuner 10, and provides the analog IF AGC signal to amplifier 30 and mode switch 60.

At step 340, signal receiving device 100 determines the signal standard associated with the currently received signal. According to an exemplary embodiment, controller 55 may determine the signal standard at step 340 based on an output signal from processor 40 that indicates the particular signal standard associated with the digital IF signal provided from A/D converter 35. According to another exemplary embodiment, controller 55 may determine the signal standard at step 340 responsive to a user channel selection input by accessing a memory which stores data indicating which channels correspond to which signal standards. Regardless of the detection technique employed, controller 55 provides a control signal to mode switch 60 that indicates the particular signal standard associated with the currently received signal.

At step 350, signal receiving device 100 controls the gain of amplifier 20 based on the signal standard associated with the currently received signal. According to an exemplary embodiment, mode switch 60 provides a gain control signal to amplifier 20 at step 350 responsive to the control signal from controller 55 that indicates the particular signal standard associated with the currently received signal. According to this exemplary embodiment, mode switch 60 provides a fixed voltage signal to amplifier 20 as the gain control signal when the currently received signal is of an analog signal standard (e.g., NTSC, PAL, SECAM, etc.). This fixed voltage signal may for example correspond to a voltage level that causes amplifier 20 to apply its maximum gain when generating the first amplified IF signal, and thereby improve the system noise figure.

Also according to this exemplary embodiment, mode switch 60 provides the analog IF AGC signal (direct or scaled) from D/A converter 50 to amplifier 20 as the gain control signal at step 350 when the currently received signal is of a digital signal standard (e.g., ATSC, QAM₁ QPSK, etc.). Using the analog IF AGC signal from D/A converter 50 as the gain control signal for amplifier 20 improves signal level handling capability in the presence of strong signals, particularly strong undesired adjacent channels.

As described herein, the present invention provides a signal receiving device capable of receiving signals of various different signal standards including both analog and digital signal standards. The present invention may be applicable to various apparatus, either with or without an integrated display device. Accordingly, the phrase "television signal receiver" as used herein may refer to systems or apparatus including, but not limited to, television sets, computers or monitors that include an integrated display device, and systems or apparatus such as set-top boxes, video cassette recorders (VCRs), digital versatile disk (DVD) players, video game boxes, personal video recorders (PVRs), computers or other apparatus that may not include an integrated display device.

While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A receiver (100, 200) capable of receiving a plurality of signals, wherein each signal includes information in accordance with a respective signal standard, comprising: a plurality of amplifiers (20, 30), said amplifiers (20, 30) being gain controllable; a controller (55) operative to control the gain of a first one of said amplifiers (20); and a mode switch (60 or 70) operative to control the gain of said first amplifier (20) for each of said signal standards responsive to a control signal from said controller (55).

2. The receiver (100) of claim 1 , further comprising a detector (45) to detect an output magnitude of said amplifiers (20, 30) and to provide a second control signal responsive to said detected output magnitude, and wherein said mode switch (60) selectively controls the gain of said first amplifier (20) using said second control signal.

3. The receiver (200) of claim 1 , further comprising a detector (65) to detect an output magnitude of said first amplifier (20) and to control the gain of said first amplifier (20) responsive to at least one of said detected output magnitude and a second control signal from said mode switch (70).

4. The receiver (200) of claim 3, further comprising a second detector (45) to detect an output magnitude of a second one of said amplifiers (30) and to control the gain of said second amplifier (30) responsive to said detected output magnitude.

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5. The receiver (200) of claim 4, further comprising a filter (25) connected between said first and second amplifiers (20, 30) and filtering an output signal of said first amplifier (20).

6. The receiver (100, 200) of claim 1 , wherein said signal standards include NTSC, ATSC and QAM.

7. The receiver (100, 200) of claim 1, wherein said plurality of amplifiers are connected in series.

8. A method for providing gain control for a signal receiving device, comprising steps of: providing a plurality of gain controllable amplifiers (20, 30) connected serially; providing a controller (55) to control the gain of a first one of said amplifiers (20); and providing a mode switch (60 or 70) to control the gain of said first amplifier (20) for each of said signal standards responsive to a control signal from said controller (55).

9. The method of claim 8, further comprising steps of: detecting an output magnitude of said amplifiers (20, 30); providing a second control signal responsive to said detected output magnitude, and selectively controlling the gain of said first amplifier (20) via said mode switch (60) using said second control signal.

10. The method of claim 8, further comprising steps of: detecting an output magnitude of said first amplifier (20); and controlling the gain of said first amplifier (20) responsive to at least one of said detected output magnitude and a second control signal from said mode switch (70).

11. The method of claim 10, further comprising steps of: detecting an output magnitude of a second one of said amplifiers (30); and controlling the gain of said second amplifier (30) responsive to said detected output magnitude.

12. The method of claim 11 , further comprised of filtering an output signal of said first amplifier (20).

13. The method of claim 8, wherein said signal standards include NTSC, ATSC and QAM.

14. The method of claim 8, wherein said amplifiers are connected in series.

15. A television signal receiver (100, 200) capable of receiving a plurality of signals, wherein each signal includes information in accordance with, a respective signal standard, said television signal receiver (100, 200) comprising: a plurality of amplifying means, said amplifying means (20, 30) being gain controllable; control means (55) for controlling the gain of a first one of said amplifying means (20); and switching means (60 or 70) for controlling the gain of said first amplifying means (20) for each of said signal standards responsive to a control signal from said control means (55).

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16. The television signal receiver (100) of claim 15, further comprising detecting means (45) for detecting an output magnitude of said plurality of amplifying means (20, 30) and providing a second control signal responsive to said detected output magnitude, and wherein said switching means (60) selectively controls the gain of said first amplifying means (20) using said second control signal.

17. - The television signal receiver (200) of claim 15, further comprising detecting means (65) for detecting an output magnitude of said first amplifying means (20) and controlling the gain of said first amplifying means (20) responsive to at least one of said detected output magnitude and a second control signal from said switching means (70).

18. The television signal receiver (200) of claim 17, further comprising second detecting means (45) for detecting an output magnitude of a second one of said amplifying means (30) and controlling the gain of said second amplifying means (30) responsive to said detected output magnitude.

19. The television signal receiver (200) of claim 18, further comprising filtering means (25) for filtering an output signal of said first amplifying means (20).

20. The television signal receiver (100, 200) of claim 15, wherein said signal standards include NTSC, ATSC and QAM.

21. The television signal receiver (100, 200) of claim 15, wherein said amplifying means (20, 30) are connected in series.