CA2066711C - Dual mode automatic gain control - Google Patents

Abstract

A gain control system for controlling signal levels of the signal received by a receiver. The gain control system is operable to control the signal levels of the signal when the signal is comprised of either a conventional, constant envelope signal, such as an FM signal, or a non-constant envelope signal, such as a TDMA composite modulated signal. The gain control system may be advantageously embodied in a dual-mode radiotelephone operable to receive both conventional, FM
signals and TDMA, composite modulated signals.

Description

2~6711 ., ' -1-DUAL MODE AUTOMATIC GA~ CONTROL
B&~glou~d of the Invention The present invention relates generally to ~7"l" ~i~ gain control Al-,v~ , and, more particu7larly, to an ~S7lltnms7tic gain control system for a receiver capable of controlling signa7. levels of either a constant envelope info7mAS;nn signa7l, or a non-constant envelope i--f- .---~: --- signal when received thereat.
A radio ~v ~ rs7t;o7l system is .,VlIL~1;3~, at . ~ - of a trans_itter and a receiver. The L.,AI..7~iiL,,. and the receiver are i. L~.- -...rctPd by a radio-r~e~lu~.l~ channel to perruit L
of an ;.,f--...~ - . signal Ll._.~.~
Typically, t7ne ;"r ..._~ signal is i u~.e~_3~ upon a radio-15 r~ uc ~ v. . .~ wave by a process referred to as mnql~ls7t;nn to permit 1.. s ~ ... of the infv7 mA~;o7l signal between the il~ll, uiLk:l and the receiver. The radio-rltu~u. .l.,~
ele~l,u.l.&r,ll ~ wave is referred to as a car ier wave which is of a particu7lar frequency, and tne carrier wave, once mn~ l-ls7tr-d by the infn7 ms7t;o7l signa7l, is referred to as a modulated, information signa7l.
The mndl7lS7tPd i~Fv~ signal may be L~ ~d through free space to transmit thereby the infn7ms7hn;A. between the L~u~ LL~
and the receiver.
Various mo/lv1-At~on ~,~1...;.l.,.5~ have been d~lv~ to 25 modulate the ;"f... -': -- signal upon the ele l.-~ ..s ~ wave.
Amrlitv~lP mnd~ nn (AM), rleu~u~A~ nAn~lllAtinn (FM), phase mn~ l. t;nn (PM), and ~ ;~ mnd~ tinn (CM) are four of such r.An~ AAtinn l~ L~ Ac 8~
In general, an ~ P mn~hllAAted signal is formed by 30 il L,V~ Ig (i.e., mA,AIll~tin~) an ;~fv n_l;. - signal upon a carrier wave such that the infArm~hnn signal modifies the Amr1itll~7P of the carrier wave CVI ~-IJ ~ -l -J? to the value of the ;~f~ ~ ---1: --l signal.
Amrlib1-lP nAn~ . t;nn does not cause the L~ulu~ of the carrier tt v~ry, t~ d th~ inl~A~ m portio~ o~ttu~ t-~l --;"F~ ., signal is contained in the shape, i.e., ~ ;e, of the signal. The shape of the .~ 7~d information signal i8 referred to as the envelope of the signal, and tbe changes in the -omr1itv~7~P of the infn7~--~;rm signal change the shape of the envelope formed thereby.
A rlG~U~ mnd~ signal formed is formed by ill~ G~ g (i.e., mndlllotine) an information signal upon a carrier wave such that the i.,r.. ~ -. signal modifies the L~u~ of the carrier wave ~u~ eto the value ofthe c~ ~n signal. F~ uc~
mn~l111Ot;~n doeg not cause the l.1;i..~.7Q of the carrier wave to vary, 10 and the iU-rUl nn content of the mn~7~ tnd r ~- signal is contained in the variation of the rl~U~U~ of the sig lal. Because the n...l.l;l...~7.~ of a r Gulu~ 7 mnd~1lotn~7~ signal does not vary, a frequency ~d~ ot~Pd signal is referred to as a constant envelope signal.
A phase mn~7vl~nd signal is for ned by i-..~.c~ (i.e., 15 mnd~ tine) an i..f~ signal upon a carrier wave ~uch that the c~ - signal modifies the phase of the carrier wave ~ul,_. l,...,.l;,~e to the value of the infnrms7ti~n signal. Phase mnd111at;~n doeg not cause the omrlitu~7n of the carrier wave to vary.
The i~ Liu~ content of the mn~717lotPd infnrm~7t;~7n signal is 20 contained in the variation of the phase of the signal. Becau~e the l-l;l- -ln of a phase mn~7~llloted infn7m~ n ~igna7" si7nilar to that of a rlt~lu~ mn~7~ ntpd signal, does not vary, a phase mnA1~ ed sign~ referred to as a const. nt envelope signa7,.
A -----I~A :l~ mn~7~ulot~pd signa7. is for7ned by i~.P~g G.e., 2~ mn~.7l71O~;ne) an ;"1~- "~ signal upon a carrier wave such that the infn7 mot;on gignal modifiei both the omr1it11~.7n and the phase of the carrier wave. ~onventionally, in order to form the ~ n~;k mn~.7~1ot~od signa7l, the carrier wave is first 8~ d into sine wave and cosine wave cv l' ~ ~ portions. Separate portions, referred to 30 as the in-phase (or I) and the ~lu&LI~Lu~G (or Q) l~ ~ -IR, of the j7~rmot;~n 8igna7, are ill~ s~d upon the cosine wave and sine wave c -- l" '~ -t portions of the carrier wave. (More particu7arly, the in-phase ~v~ - .- .t. of the ;,~ru....~ . signa. is i u~ ..,c~ upon the cosine wave ~ 1 of the carrier wave, and the ~U~ I O I G

.. ~

- 3 -f~ of the information signal i9 Il~.~ULCl~.ed upon the sine wave -'L"'"""I of the carrier wave.) The sine wave and cosine wave f.~- ..I~J ~ are then ~ .f,.l.:..PA and the resultant signal, the mnA..1 ' signal, varies in both Amrlit~l~lP and, 5 ~?A~3;tinn~Ally, phase. Composite mnAUlat;^n is alv in that a cnrr~rna:t~ mnA~latPd signal permits a greater amount of inF~rmAtion to be 1.~ within a r cuu_.~ ~ bandwidth tban a signal Alcd by any of the previously mPnt;~>nPd mnA~ nn ~. ~ "'a A receiver which receives a mndlllAtpd ;nr..-...A~: -. signal, 10 such as a one formed by one of the above-degcribed mndlll~ti~m techniques, includes circuLtry to detect, or otherwise to recreate, the ;,.r.. -~i .. 8ignal mnAU~AtPd upon the carrier wave. This process is referred to as ~pmnA.~l As many different mAd~ tP~
;nr~ l --. gignalg may be n;m~llt~np~aly ~ . I ~d by a plurality 15 of L~a~u~ s at a plurality of different r.e~lu~ , a receiver contains tuning circuitry to APmAA~IlAtP only those signals received by the receiver which are of certain desired r.c~u_nc;ea. The broad range of f c4uc--cifa at which mnAlllAtP~ infnrmAAt;^ n signals may be i8 referred to ag the Flf_~ LI.~ r.~luc..~ spectruAm.
20 Regulation of radio-L- ~uc ,~ ff~mmun;c^~;nna in certain r ~ v bands of the el~_l. ..-- ,;.. l:f. frequency spectrum n.;f.;l.. F
r e~,e between sim~ Fv- -ly ~,A- AI I/æd signals.
For example, portions of a 100 MHz band of the ele~ Acl"~ r r, cu~U~ .V spectrum (c.~cllJi-.~ between 800 MHz and 900 ~IHz) are 25 allocated for r~infelF~hone ~ ~,"""~,;~1 ~n, such as, for example, v -~ d by .AA;.,I 1 ~.h...-Ps utilized in a cellular, system. Existing ~ d;. -' .' contain circuitry both to generate and to receive radio-r.c.luc~ nJ"l_l- d inff~rm~tinn signals.
A cellular, c .. :. ~ nR system is created by p~- :l: --.;
Uul ._.uuB base stations at spaced-apart locations lluu~ u~l~ a ~;CU~ area. Each of the base stations is ~u~ lC~ to rece*e and to transmit mnd~ tpd infnrmot;- n signals Riml~l~AI.ro~.Aly to - . 2066711 --

-4-and from ~ to per_it two-way ~ -n LL. .~,~t .. ~
The base stations are p - - ~ at locations such that a r~ r1. L.1~....r at any location LLuu LuuL the ~..~ area is

5 within the reception range ûf at least one of the base station receiYerS.
The ~,~ G~;l~Li~l area is divided into portions, and one base station is pr, l: .nF.(I in each portion. Each portion of the gcu, 1;* 1 area defined thereby is referred to as a ~cell.
Although l~UI~ Ouct m(ldl1ls~t~d infnrms-tion signals may be 10 ~ir~ A~Pr~ y ~ d at different 1~ ~~ rl~. ,r ~1 each mn~ t~d inf~rrn~h~n signal, when l.... ~ occupies a f~nite portion of the f,cqu_n~ band. O~ ",u;-.g of ~in~ u-ly L...f~ - d m^dll1s,tr~fl, infn~ n~t;~m gignalg in the 8ame ~rt. r~ l-;r area is ;" l'~ r~1F as i--Lclrclc.lcc between overlapping signals at 15 the same Lc~luc~ could prevent detection of either of the Ll,- - ~- ;l l-~d mn~ trd infn mst;~m signals by a receiver.
To prevent such ~ il~, the rlc4u~ band allocated for .."""".;~ n i8 diYided into channels, each of which i8 of a 30 KHz rG~I~;lL~l. A first portion, ~. ~ ~. ..1;. .~ behween 824 MHz and 849 MHz of tbe L ~.~U_.II~ band, is ~llocated for the tr~n~ni~ of m~d~ t~d ;..r~ :- -. signals from a ~ d~ to a base station. A second portion, ~. ~.,.1;..~ between 869 MHz and 894 MHz of the LC~1UCI1L Y band is allocated for the of mn~ill1Ft;~n inf(lrmstjnn signals from a base station 25 to a r9~int~1r-Fhnnf.
Increased usage of cellular, ~ ;r_l:on systems has resulted, in many in~tts~ F~ however, in the full 1lti1i~st;nn of every available L, channel of the frequency band allocated for cellular, .~ l. --.c . - .. -.~ ... Other rl.;~lu_..~ bands of 30 the el~ - s.,,- -~ Le~lucll~ spectrum are ..lt . ~. I; . . .r ~ similarly fully utilized.
Various attempts have been made to utilize more efficiently the r.c4u .l. ~ band allocated for ra~ . -.t to increase thereby the illr~ Liull l.,.. ~ .. -. capacity of a cellular, 20667~1 --n gystem. Attemptshave been similarly made to use more efflciently other r~U,Ut~ J bands of the ;P r,~lu~... J spectrum.
Conventionally, the mA~1at;~n technique utilized by ~ L - ~- """" ~ On systems to form the mnd~ tPd signal thereby is r,e~vell~J rpp~rlu1at;~m As - ~ ---Pd previously, a r ~lu~ J n~ u1a~Pd signal h~n.,~ ,3 an inf~)rm~b~An signal upon a carrier wave to modiry the r~ U~.I. J of the carrier wave according to the value of the P signal. However, 10 ~uu~_.ltiv"~l &~lU~ ,J mot~ V~ form a ~ VA
wave, FM mo~lu1atPd signal, and only one such cullLinuu. wave signal may be Ll ~ ~A.~ ';I ~ .1 upon a; channel at a time.
Tc~l~uque3 have been developed, wbich permit L- ~ of more than one signal at the same rl ~ u~.l.. 1 . One such k ~
15 involves the sPq~Pnt;a1 L~c ~A hlg of a single channel by several ".. 1:.. l- 1. ,.1l.. ~ Thig L~I~PIque is referred to as time-domain multiple access tor TD~A).
In order to use TDMA, an infnrmahon signal (such as a voice signal) which is to be h~ -1 is first encoded according to an 20 encoding scheme. Once encoded, the ;..r""\,_ti ~ signal, in encoded form, is mn~ tpd upon a carrier wave and is Ll~...rA-..:II ~d in bursts. Other i .. f.. - ~ :v ~ signals may similarly be encoded" ~ t- ~1 and 1 . A~ - d in ;..l~ bursts at the _ame r,t:.lu~ .J. Thùs, a greater number ;.~r.. -1 . signals may be 25 i 1 within a particular frequency lv~,l~;~. When the jnFol rn~t;^-~ signals are ~ d by users of ,~-l: ,l 1- l l,- PA
forming a portion of a cellular ~ system, a greater number of l. 1:~t~1~ ,~1.,... ~ may be operated within a particular r ~ ~Ut~ll~ ~ bandwidth when such a TDMA technique is utilized.
A receiver consb ucted to receive a TDMA signal, such as a TDMA ~ 7;lt mnd~ t~pd signal, reconstructs the original ;--rv~ :- - signal ~vy decoding the TDMA signal L~ d to the receiver in ;~-l~ . . .:1 1- ~t bursts.

- 2~66711

-6 -A system which utilizes ~v ~ n~ mn~ ntPd signals which are l~ d utilizing the TDMA ~vlu~4uc has been chosen for a system to augment existing United States domestie cellular v.~e systems. C~ ~ lity between esisting domestie cellular 5 ~I~ l.hu~.~ systems and the proposed system is n~C~ to permit ev~ u~ u..k3d for use on the proposed system also to be used on the existing systems. Thus, ~.1;..~ 1, II---.F~ are being eonstructed which are eapable of receiving both FM, c onhnuA~ wave signals, and TDMA ~ L~ ;lp-mnA~lntF-~d signals. Such rn~ F~ may 10 be suitably ûperated in a ~v~ Lul~al cellular v --- .-~ v ~ system which utilizes FM ~....I.;n...~ ., signals, and in a eellular, system whieh utilizes TDMA; ~ mnd~1Dted signals.
A receiver ~ Dll u~ kd to receive TDMA ~ "{-F~'d 15 signals may also require circuitry to perform F,'q 9li7:nt;~l~ in the reeeiver. Equalizer eireuitry is required to eorrect for delay problems ~d with refleetions of signpls l~ 3~1 to the receiver which arrive at the receiver at different times Because the signal received by a receiver is aetually a vector sum of all signals 20 L . - :~ ~ d at a p2rtieular r ev,u, ~. ~, the signal received by a rece*er may aetually be ~ of the same signal at different times as the signal may be reflected off objects prior to reception thereof by the receiver. The signal actually reeeived by the receiver is, therefore, the sum of all signals which are l,.~ d to the receiver 25 along many different paths. The path lengths may vary, and hence the signal actually received by the receiver may vary, ~el~,UU/~ to e of the receiver. Equalizer eireuitry is ~ formed by a processor having an c~ ulu~l;a~e software al~;u~;ll~ embûdied therein. In order to permit optimal operation of the equalizer 30 eireuitry, the receiver should be cv..;,l.uclc~ to be linear (i.e., the ~lPmnAlllntpd 8ignals ghould represent L_~uLt-L~Iy the original I and Q
portions mndlllnt~pd onto the carrier).
The linearity of a receiver defines the e~iciency of the ,o~ rl of a received signai. An ideal receiver ~e~uvlu~a only the 2~6~711 .

-7-signal l~ n;~ thereto. Actual, nonideal receivers, through a process of ~mrlifi~-~t;~n and mi~ing occurring during r tuu~ J
Cull~a;u~ of a received signal, produce ;~I..-,,,,~,I,,l^~;~n distortion.
~a~O~I~t~ad with ;..I~ J..l 'nn distortion are ulld~ d spurious 5 signals "v.._.c.led during r ~u,u_~ ~ cull~i. of a signal received by a nonideal receiver. Such u~d~ d, spurious signals are referred to h~ ;Lb~l~,.. a8 ;~ -bJl~t;nn spurs. A highly nonlinear receiver gonor~ a large amount of i~ . ".n ~ hnn distortion.
Typically, rece*ers, including those utilized in a . un~wlLû~al, 1 û cellular rpAi-~' ', ' ~ ~ ------- --; vl ~n systems, r~inimize the Aal~atarin~la effects caused by the ~ . of ;..t~ ...n~ t;nn spurs by including, as a portion of the receiver circuitry, filter circuits to filt_r the ull~ signals and reduce the level of ;..~ lulot;nn spurs ,,_.~ ~d during r~ u~ Ull~.~Ull of a received signal.
15 Such filters may be ~ ~ of either active or passive filter stages.
An active filter stage may be ~lv ~ ly embodied in an Lu~ d circuit, but an active filter is gener21ly linear over only a limited dynamic range of received signals. AAAihnn~lly, an active filter exhibits proper filter char~.~taria~i~ a over only the limited 20 dyna_ic range.
As note,d h~.~, .l~UV~ because a mnd~ t~a~ infnrm~lt;~n signal at a particular r~ u~ may be reflected off objects priûr to r~ception thereof by a receiver, the signal received is actually the sum of many signals received from many different paths. Hence, the 25 signal level a.e. pmrlitl~Aa) of the received signal is actually the vector sum of many signals received from many paths. The number of, and intensity of, signals actually received by a receiver may vary over time as a result of l~ of the receiver, ûr of the objects from which a ll ~ d signal is reflected. As a result, the signal 30 level of a received FM signal varies over time. This variance is referred to as "fading of the signal. The rate at which the resultant signal strength at the receiver varies is ~.~A ~ -- lly Aat~arminad by how rapidly the receiver is moving through its t~llVilULUll_.lt, and the frequency of the cbannel being used. For instance, in the cellular ` ~ . 20~6711

- 8 -r.e~u.:.. ~ band, and when a cellular rJ.di~ is pAo;t;onPd in a vehiele travelling at si~ty miles per hour, the signal strength of the received signal ean vary by h,up.u~i..,~.l~ly twenty decibels during a Sve m~ ecr~nrl periûd.
Cu,.~ Lu.. al FM receivers utilize voltage li_iters prior to signal rl~Pmr~ lst;or~ whicb clip the received signal. The resultant signal is of a constant envelope, and the ~rl~ t :r...~l effects of fading are thereby \.;-: : A Since the i~r~ in an FM signal is not earried in the envelope, clipping the received signal to form a signal 1 û of a cûnstant envelope permits optimal recovery of the L ~luell~y mn~ t;- n and, hence, the infrrm~t1An content, of the reeeived signal. Gain control of an FM-only, ~- ,/ ;,A,~ v receiver is not r ? .~ for rl~PmAdlll~ n~ though sueh gain eontrol may be utilized to adjust the received signal level to permit optimal ûperatiûn of 1- r~ " and filtering eire~itry within the receiver.
Receivers ~u~lbLu~.led to receive a TDMA c~ ur l~-modlllstPd inPr~rm~t;An signal, however, require gain control eircuitry to correct for the effects of changes in signal levels induced by fading, and to allow recûvery of the i,.r(.. -1: .. , ., .. r.. .~" encoded in the envelope 20 of the signal.
Beeause .~ h~ being cu..;,~.u. l~d tû permit ~lPmr~ n of TDMA ~ G~ -mr~dlllsted signals are also to permit rlpmAd~ n of cûnventional, c4 ,l;""r~ ~ r~v signals, the ' ?~, ~ ~ must be cu..s~. uc~èd to contain gain eontrol cireuitry 25 to correct for the effects ûf changes in signal levels of TDMA
mn~hll~tPd ~ignal8. Such gain control circuitry may also serve to ensure optimal p . f.-- .rA .r~ ûf the receiver during reception of ~,- --1;- ..- - ~ ..~ signals. The form and p~. r~- ..._r~ '~ of gain control eircuitrv may vary, though, depenrline on the type ûf 3û mr~rllllst;~m being received.
When a r r~ ;~ mr~rllll~ted signal is received, gain control circuitry should be of a design to per_it rapid and --1 ;1~. - --~traeking of variations in received signal levels due to fading. In addition, a ~ hA lP which generates a TDMA r ~

2û66711 g mn~ d signal to transmit an ~ - signal in a cellular system also raeasures 1~, the signal strengths of l~ A located in one or more cells. This process of testing signal strengths is referred to as mobile ~ - ~ted hand-off (or 5 MAH0). The MAH0 test also requires gain control circuitry which permits rapid and ~ IA tracking of a signal.
Digital signal i~lV~SJu~ may be utilized to form such rapid-trackirlg, gain control circuitry. However, digital signal , require A ~ amounts of power for operation. Cellular, 10 rsr~ ui,ul..~.lL may be battery powered; for ~uch ~luiy~ ~L~ u~ use of digital signal ~u.. r~ circuitry to perform g~un control may create an uud~ power load on the battery when the receiver receives a c --.l ....~ wave FM signal.
When receiving an FM-mnd--l~tPd signal, the gain control 15 circuitry need not be of a design to track fading (i.e., the gain control circuitry need not per_it rapid and ~ tracking). A normal FM limiter dpmA~ t^r is i~s~.lsiLi~., to the v~l;aliu..~ induced by fading, and the ~u.- ..- .l: --.Pd MAH0 operation is not p~,.fu~ d during cvllLil _ wave reception. For CUlliiL_~ j reception, 20 slow-resp-An~lin~ gain control circuitry cvll~Llu~,L~d with anaiog circuit elements which require only low power for operation thereof is possible.
A ra~ t~l, ' - - operable to receive both .~ullv~ iullfil c~ P _~_ signais, and TDMA c~ :lp-moc~ Atpd signals 25 having gain control circuitry for controlling signal levels of either type of L~ d signai, and, Arl~lition~lly~ having minimai power ,: i~uil~ L~ would be &vvA~ 6~us.
What is needed, therefore, is a gain control scheme which requires minimai power ~ , but which aiso may be 30 aiLu.l._L~ily operated to control signal levels of either cull~,.,Liu.l&l, cul-Li~_ . ~ .v-vt n~o~llllAtpd inff~rmA-t;r~n signals, or TDMA
--mnrl~ ~ I A t,Pd: .. f~ .... A I 1 signais 1 ~ d to the rnP

-10- Z06~711 y ~^f thP TnvPnt.i~^n It is, ~Accv~Lu~;ly, the object of the present invention to provide a gain control system for controlling signal levels of a signal received by a receiver operable to receive both (, - . ~ :.. ~P. ~c, and TDMA
~^omrn-^ te-moA~lls tpd ;"f, .. " ".t ~ signals.
It is a fiArther object of t~e present inAvention to provide a g.nn control system, operable to control signal levels of a signal to a receiver either by conventional, ~ u~ wave 10 n^Arlvl~t;^~n ~ u~s, or by cnmri^Rit,~ m~ llP~ n tP~A~hn;rlllpR~
which reqlAires mirimal power r~ : . for operation thereof.
It is yet a fiArther object of the present invention to provide a du~l-mode r~ ^ operable to receive both a conventional, ,^-.^ntln~ llR wave infArm^~t;on signal and a TDMA v~
15 mr~ 1 signal having gain control circuitry of _inimal power uil ~lU~ArA~
In ac.,ul.l~.cci with the ptesent invention, therefore, a gain control system for controlling signal levels of a signal received by a receiver is disclosed. First down-conversion circuitry converts the signal received by the receiver into a first 20 down-converted signal of an ;"1~.",..1;,.1~ frequency and of signal level ~ ~ ~,1 l; l ".1. ~ -LIiV~ of signal level nn:~ni~ lPc of the signal received by the receiver. Variable amplifier circuitry is coupled to receive the first down-converted signal generated by the first down-conversion circuitry. The variable 25 amplifier circuitry generates an amplified signal of the; ' " frequency at an ~rnr1ifi~ n level ~ollu.,,uù..li..h to a gain coefficient of the variable amplifier circuitry. Second down-conversion circuitry is coupled to receive the amplified signal and converts the amplified signal of the ;"~ . ",. ~ frequency generated 3û by the variable amplifier circuitry into a baseband signal of signal ~evel "~ "c l~ultscllt~,~iv~ of signal ~evel m:l~ni~ PC of the signal received by the receiver. First signal detection circuitry is coupled to receive the baseband signal generated by the second down-conversion circuitry and converts the baseband signa~ upward in frequency to form an uucullvc;lt~d signal. The first signa~
~.

- lOCa) - 20S6711 detection circuitry is also coupled to receive the u~ ~nlvc;lL~d signal, determines values of the signal levels of the signal received by the receiver when the signal is comprised of a constant envelope signal, and generates a first gain control signal responsive to values of the signal levels dpl~rm~ thereat. Second signal 5 detection circuitry is coupled to receive the baseband signal generated by thesecond down-conversion circuitry and determines values of the signal levels of the signal received by the receiver when the signal is comprised of a non-constant envelope signal. The second signal detection circuitry has, as a portion thereof, a digital signal processor, operative during times in which the signal received by 10 the receiver is comprised of the non-constant envelope signal and non-operative during times in which the signal received by the receiver is comprised of the constant envelope signal, and generates a second gain control signal responsive to values of the signal levels determined thereat. The gain coefficient of the variable amplifier circuitry is adjusted by alternately applying either the first gain 15 control signal or the second gain control signal to the variable amplifier circuitry.

2~6711 Brief Description of the Drawings The present invention will be better und~,O~vod when read in light of the ~r~ lg drawings in which:
Fig. 1 is agraphical e~ of an ~........ r.~ r mr~ tPd --. signal ~ of one ôuch signal which may be utilized by the gain control system of the present i~ iVII;
Figs. 2A and 2B are graphical ,~ ot;.~ of constant envelope signals wherein Fig 2A is a r~ u_..~ ~ m~ signal 1 0 l ~ of one such signal that may be utilized by the gain control system of the present invention, and Fig. 2B is a phase mr~ll.lotAd signal l~p.~ a~ of another such signal that may be utilized by the gain control system of the present ill~ .iVIl;
Eig. 3 is a graphical le~vl~ of the rrrr..t~ tirn points of 15 a discrete encoding scheme which may be utilized to encode an i~f- ~ -- gignal to form thereby a discrete encoded signal;
Fig. 4 is a graphical l~Z~l. e- .I~t;rn of a rA~ ul~tpd informPt;~n signal graphed as a function of frequency upon a particular tr~na nioo;~n channel, and ;~ n~ tinn spurs, graphed as a 20 function of rl~ uell. ~ Led during down cv..,~.c,;on of the received . ~ rn ...~ ~.Y signal;
Fig. 5 is a block diagram of the gain control system of the present ill~.,.lt.iVI~;
Fig. 6 i8 a partial ~ ~ partial block illustration of a 25 preferred ~- " ' ofthe present ill~ tivll~ and Fig 7 is a flow diagram l~.ce~ illg the method of the present ..lio.,.
DP~rrirtirn of the Preferred ~-~
Turning first to graphical .~. - - .~ of the Figs. 1, 2A-2B, fv. u8~ ~ti~ofthreetypegof mn~ tP~7;..r...,~..~:....
signals are shown. The system of the present invention controls signal levels of a signal received by a receiver which are similar to the -12- 2~667~1 fULLA-S of Figs. 1, 2A-2B (or, more particularly, a ~taV~fULLU
similar to the wav~form of Fig. 2A, and a waveform similar to the --. of Fig. 1 and Fig. 2B~. The ~c.t~VILU8 are actually plots of voltage, scaled in terms of n~illivolts, on ordinat_ axes 10 as a 5 function of time, plotted along abscissa a~es 12.
Waveform 14 of Fig. 1 is an flmrlibl~lP ,~ d signal formed by m~lc~ atinG~ an ;.. f.. A~ signal upon an ele~ wave wherein the ~...I.l;l ...1~ (i.e., voltage) of the waveform 14 varies v~ to values of the ;..~ I ^ . signal mnd~latPd IL~ uul..
1 û The ;.~ . bearing portion of waveform 14 is, thereby, contained in the ~ lP of the waveform such that v in the 1 of the waveform 14 cv..~, ~ to variations in the arArlitll~P of the ;..fi ^~I: -- gignal. The amrlitll~lP of ~ fv~LlL 14, referred to as the envelope of the waveform, is ~e ~u~ I in Fig 1 by 15 curve 16. Curve 16 is si~lar in shape to the r ~' signal, which, when ' ' ~d upon an Gl~ :c wave, form8 waveform 14. Waveform 14 does not vary in fi ~4udh~ and the frequency of ~ t~fUlLL~ 14 ~ û~ u~ld~ to the rl~.lu~L.~ ~ of the l-nnnA~l..lf tPd wave G.e., the carrier wave) upon which the 20 infnrmati^n signal is mn~ t~(l Such r.eu,u~ is referred to as tbe carrier rlequ~..~ of ~vc.v~ru.Lu 14.
Waveform 18 of Fig. 2A is a L~ u~ mntllllatPd signal formed by m~AlllatinF an ~ signal upon an elc. ll- -~E; .~ ~ wave.
The... l-I:I lrofwaveform18doesnotvary. Ther~u~.../of 25 v~ fv~LL~ 18, however, varies l~ vlL~L~ to valueg of the in~rmf~t;~
signal mn~ lf 1 thereupon. Variations in rl~U~ rl~ of ~ rUlLlL
18, thus, form the ;.,f --. ~ -c ~ ~;I.;l.G portion of the ~ fv.L~.
The variation in f~ u~ of waveform 18 caused by mndulflt~ of the infnrm ~ n signal upon the d~ ,, ^ wave is, however, 30 slight compared to the rl~:U,Ut~ of the ~ IlULuf~ wave. Hence, waveform 18 may, similar to the waveform 14 of Fig. 1, be c~ d by the r.du,u~ of the el~ , - wave (i.e., the carrier wave) upon which the ;ILrUlLUC.l;UII signal is mn~ lPtP-l such r.~:u,u~ is referred to as the carrier fi~:u,ul~ of v,~. fu.~.. 18.

` ~066711 Waveform 20 of Fig. 2B is a phase mn~ At~td signal formed by thl1~ an ;"r~., c~:~p, 8ignal upon an el~,lL ~ I r wave.
The ~"~rlibl~P of waveform 20 does not vary. The phase of the _fUI I 20, however, varies le~ O~ , to values of the infrt~tnqt;o 5 signal Inndl~lAt ~d thereupon. Variations in phase of the ~i~._f~.lu, thus, form the; . . r~ v~ ,t.: . .; . .~ portion of waveform 20. It is to be noted that the abrupt phase change of waveform 20 of Fig. 2B is for purposes of illui.~. only. An actual phase mn~lul..t~.d signal would exhibit a gradual phase change. The phase variation of 0 ~r~t . & 20 does not L;i,;~ ly alter the carrier rL~ u~ of the signal. Therefore, ~ fulul 20, once ~ d~ may (similar to waveform 14 of Fig. l and waveform 18 of Fig. 2A) i8 said to be ch~c~to.;~ by the carrier r t:-lu_..cy of the ~ fu~lu.
Turning now to the graphical ~ I.nl ;ntl of Fig. 3, the 15 r~ono~ t;~tn points of a discrete encoding scheme for encoding an ~ " signal are illustrated. A~ d h~.~;L~ , by encoding an infn~L~t;~n signal into a series of TDMA ~ O~IP
nn~d~llAt~d signals, more than one signal can be opqvpnt;qlly at a particular r~u,uen~ to increase oignifirAnfly thereby 20 the informAt;on -~l capacity of a particular r~e.
band.
Fig. 3 illustrates an eight-level phase shift keying (PSK) sy~tem in which an ;-~f~ n signal may take the form of any of eight different levels a.e., phases). Other discrete, encoding schemes, are 25 of course, similarly possible. In this system, the inf~rmAh~n signal is encoded into two parallel bit streams referred to as I(t) and Q(t). At the sampling instant t;, I(tL ) Q(t; ) form a vector whose possible values are hl p} lly .e~ .l in Fig. 3 and referred to in the Figure by reference numerals 26-40. Ordinate axis 22 and abscissa a~is 24 ~re 30 scaled in terms of ..-A~ A~ of Q(t) and I(t).
Such a vector may be m~ At~d upon an cl~ L..~ wave to form thereby a c-----~ mnrllllqtPcl information signal wherein the ~ " content of the signal is ~ l of a series of discrete signal levels (or phases). The encoding scheme of Fig 3 -~. ` 2~6711 illustrates the stsndard selected for digitsl, cellular .
systems to be impl I in the United Ststes.
With pL~ L~ 1.9r respect to the United States stsndard, only four J;rr~ chsnges between sny two 3~lu~.lL;61 vectors sre 5 p ,,,~ A Such an encoding scheme is referred to as a di~.~ulial .At., ~''-'.~ phsse shift keying (DQPSK) system.
Turning now to the graphicsl le~ m of Fig. 4, a Tnr~A~ tPd i~ 8igngl i8 plotted ag a function of L~lu~
wherein the level, i.e ~mrlitllA~ of the signsl, scsled in terms of 10 volts on ordinate sxis 50 is graphed as 8 function of L~ U~ scaled in terrns of hertz on abscissa sxis 52. The energy of signal 54 is typically centered about a center r~ u~ll~, , of a particular r ~ ~u_.~, and, as illustrated, is ~ ... U~ll;~l about line 56, shown in hatch, defined by the center rl . ~u~u~ .~ . Typicslly, a receiver receives 15 not only the desired, mndlllS~t~pd ;~r"~ signsl, ~ 3~.l1e~ here by waveform 54, but"lA 1 l :.~ lly~ other signsls located at other frequencies close to waveform 54. For purposes of A~ ;- e the ;..~- . -': --- content of the desired mnA.~l~tPd ;..r- .---l: --. signsl, such signsls are uud~D;I ''? Such signals are Itp..~ d in the graph of Fig 4 by ~ 57 and 58 Mixing processes occurring during r.~ut u..~ c u"~c.~;v" and ....~ f~l -. of the signals received by a receiver generate rn nhinsf;nn~ of received signsls, i.e., ;on spurs, which are l~ .lle~ in Fig 4, in hatch, by spurs 60 snd 61.
T .. ~ n 8purS may be of ~ ut:l,cie3 to interfere with the desired infn~f;on signsl. Such iull,_.f~ e can prevent accurste A-~ of the inform~t;on content of a received tPd ;. .rV . -i :~ ~ gigngl. Spur 60 i8 I ~;~u~ of such a spur which ;llte.f~ .~8 with a desired ;..r,~....~t:~... signsl, and, as 30 illustrated in the Figure, is of a rlt:~utll~ which interferes with _fu.. 54. In order to minimize il~ie.r~.~ ..~ caused by t;~ n 8purs, receiverg typically include filter circuitry for removing signsls, .~I.,eL~ ~d in the Figure by ~ r~,l .B 57 snd 58, to prevent generation of ;.-~. ...~..11-1-~;r~n spurs, such as spur 60.

~ 2066711 As noted plC. ;UUDIy, filter circlAitry may be r~ of either passive or active filter " l ~- ~- A receiver operable to receive TDMA ~ lDtP~l signals must further cont2in gain circuitry for InA;.-l- ..;..e the signal level of the received h,~" "nn 5 signal witbin a desired range. Such a desired range is .-c~,s~
in Fig 4 by lines 62 and 64. To maintain a signal level within such a range, the gain circuitry must amplify the signal when the received signal is of too small of a signal level, and attenuate the signal when the signal is of too great of a signal level.
As --~ d p~,.ioUDly~ a digital signal processor may be utilized to form a gain control circlAitry for controlling signal levels of a signal received by a receiver. However, a digital signal processor requires a :,~..;ri. A~l. amount of power for operation thereof. Because TDMA r ~ c;lP-Tnn~lllAAfpd signals are ~l ' only i.. l.. ~ I.ly~ a digital signal processor need only be operated during those times in which the signal is received by the receiver.
While a digital signal processor may be utilized to form gain control circuitry to control the 8ignal level8 of a ~nT ~.nll~...r A~
signal rece*ed by the receiver, the processor must be operated ~ ly~ thereby requiring a oic~ifi(~ont amount of power for operation thereof.
Therefore, and as mPnt;~nPd ~. .iU lDIy, the ~ ' of gain control impose confli~hne l~ U~ D for FM signals and TDMA ~ d signals.
Turning now to the block diagram of Fig 6, the elements of the gain control system of the present invention are shown in filn- ti~nol block form. The gain control system ~ ubo~illg the present invention is operative to control the signal levels of a signal received by a receiver when the signal is either a TDMA rn~rn~;tP-mntl-llstPd infn~-A-oti~n signal, or a conventional, ~ -- . I i . . . - - ~ wave, mod~lotpd i--ru.~.iu.. signal. A digital signal processor iB operative only when the signal received by the receiver is a TDMA .~ -mn~lvlste~1 signal, thereby -~ the power . ' of the processor.

- 16- 2~6711 The; ' ~ signal, either a ~uu~ Liullal, ~ wave ~ibnal, or a TD~ P mnd-~lAtPd signal is I .~ d to an anterlna (or other ~I~. L. ~ wave receiving device) 80. The signal received by antenna 80 is filtered, and supplied to first down W~.,.D;U~ circuit 84 on line 88. Down CU~ .D;UU circuit 84 converts the L1~ . r.. ~uell~ ~ signal (which may, for example, be of 890 lu~_h_.L;G) into a signal of a lower rl_~u_.,~, such as, for example, 45 megahertz. Down ~U ~_.D;UU circuit circuit 84 gPn~ --' - the lower rl~ ~u~ signal on line 92 which is coupled to gain control amplifier 10 circuit 93. (In other ,~ A, gain control am~plifier circuit 93 may be -" - '~, p~ ---.Pd at other locations to perform a similar function.) Circuit 93 gPnPrPtPiA, an a_plified signal on line 94 which is supplied to second down CU~1~ _. D;(J l circuit 96. Second down ~Ul~_.D;W~ circuit 96 converts the signal supplied thereto on line 94 to 15 baseband signals. Down ,UUt_.D;Oll circl_it 96 gpnprptp~ an in-phase signal on line 100 and a signal in u~ d therewith on line 104.
The in-phase signal ~ellel~ed on line 100 is supplied to baseband filter 108, and the ~I~L~Lule signal b~ Le~ on line 104 is supplied to baseband filter 112. Down CV11~j.D;U~1 circuit 96, and filters 108 and 20 112 may together comprise a portion of a single ;~ "t-~d circuit chip, referred to as a zero ;..l "r~ rl~u,u~ (ZIF) circuit illustrated by block 116, shown in hatch.
Filtered signals gPn~r~tpd by filters 108 and 112 are ~
on lines 116 and 120, vD~uc~ ly. E ilters 108 and 112 contain 25 L ' to pass signals of desired rl~u, - -t ~f When antenna 80 receives a TD~ .. P~;IP m~ t~Pd signal, the filtered signals ,5_.l . I by filters 108 and 112 are supplied to analog-to-digital ~Ull~ ~,. h. D 124 and 128, l~ p~ ly. The digital signals generated by A/D ~ ull~e~ LelD 124 and 128 are supplied to digital signal processor (DSP) 132 on lines 136 and 140. Digital signal processor 132 processes the digital signal supplied thereto, and generates an audio signal on line 142 indicative of the inff~rm_ti~r~
signal Ll~ d in TDMA c~ P mn~ tPd form to antenna 80. Digital signal processor 132 also generates a signal on line 146 ~ 7~

.0, ~, to the signal level of the signal received by antenna 80.
The signal gpnprlqt~pd on line 146 ~y be utilized to control the signal levels of the signal received by the receiver and which are eventually ~ol~lulu~ev~ on line 142.
When the signal ~ d to antelma 80 is a CUI~ LiUl~
r ~ IY wave signal, the filtered signals ~ O~ Cvl by filters 108 and 112 are supplied to up uuu~O...;u.. circuit 160.
Up ~uu~.~uu circuit 150 converts the filtered in-phase and filtered ~r- ' ' ~O phase signals gpn~rntpd on lines 116 and 120, ., , ~ ly~ to higher r.v~u~ signals, and adds the two ~ The resultant signal is b~ d on line 152, and supplied to ' ~ 1 circuit 156. The signal gPn ' ~ d on line 152 is supplied to d( - ~1 ' ' circuit 156. The ~lpmnA~ nn circuit 156 ~ - ' lnt~ the signal supplied thereto by conventional r~o~u~ d ~ nt~ h~ Cvu~,.D;v~oftheba8eband signals "~ . ' ' on lines 116 and 120 into a higher ~~ is required for ~Pmn~ul~t;nn by conventional dpmod~ tinn circuitry D - n~ . circuit 156 genOrates an audio signal on line 158 which is .e~.O~ tive of the ;~f ~ signal portion of a convent,ional, ~ wave motlvlnt-pd signal received by antenna 80. As illustrated, up <iU~.,.D;Ul~ circuit 150 and dpmn(llllntinn circuit 156 _ay a~ t~ y form a portion of ZIF circuit 116.
Z;IF circuit 116 also supplies a signal on line 160 to switch 162.
The signal ~;O~ t~d on line 160 may be utilized to control the signal levels of tbe signal received by the receiver which are ~ uvlu~ôd on line 158. The signal ~ d by digital signal processor 132 on line 146 is also supplied t~ switch 162.
Switch 162 nl~ connects lines 160 and 146, and the signals i 'I ~ thereon, with line 166 which i8 coupled to gain control amplifier circuit 93. Switch 162 is actrated by an external signal supplied thereto on line 164. When switch 162 is actuated to connect lines 146 and 166, thc signal gPnPr~t~d on line 146 is supplied to g~un control amplifier circuit 93 to control the signal levels of the signal received by the receiver which is 1 O~UI uvl u~;od on line 142. When , switch 162 is actuated to connect lines 160 and 166, the signal gPn~ on line 160 is supplied to gain control amplifier circuit 93 to control the signal levels of the signal received by the receiver and which are eventually i~L~IUC~ on line 158.
Turning now to the partial block, partial ~1.. A~AI r diagram of Fig. 6, a preferred ~ of the A..~ n I r gain control system embodied by the present invention is shoA~n. The gain control system '- ~iUlg the present invention is operative to control the signal level of the signal received by the receiver when the signal is either a 10 TDMA . ~ lotDd inff.rmot;~.n signal, or a c("lv~llLiu..al, ,ul-Li ~ wave ~ Aled inf ~rmAt~ rl signal. A digital signal processor utilized to form gain control circuitry is operative only when the signal received by the receiver ig a ~omr~U;tP m~-dlllAtPd signal.
The L. - - - I l, ~l signal, either a . u.. ~_.. Lio.,al, c- .~
wave signal (e.g., an FM signal), or a TDMA ~ m~ loted signal, is l~ IL~ by a l~ , here 8~1. C~ lly indicated by i : '~ tower 178, to an antenna (or other elt_L. ~--- ~;". - -' :c wave receiving device) 180. A signal received by antenna is supplied to filter 182 on line 184. Filter 182 filters the received signal. A
filtered signal filtered by filter 182 ic ~,_..~ .AAL~ on line 186 and supplied to mixer 190.
A~ it;~rlolly supplied to miA~er 190 is an oc~illotine signal t ~ by an oscillator forming a portion of a first phase locked loop (PLL) 194 on line 198. MiA~er 190 generates a first down ~ _.ulu.. signal on line 202. Mixer 190 converts the signal received by antenna 180 and filtered by filter 182 from a ~."~
rL~ r (which may, for eAvample, be of 890 MHz) into a signal of a lower r.e~lu~.,. .~, i.e., the first down . u..~ ,h,.. signal (which may, 30 for example, be of 4~ MHz).
Filter 206 filters the first down-conversion gignal and gPnPr~otPg a filtered signal on line 208 which is supplied to amplifier 209.
Amplifier 209 generates a signal on line 210 which is supplied to IF
inputofzero;..l~ . -, 1.AIP r.c~lu ~ (ZIF)section214. ZIFsection214 ~ 20~

contains circuitry (not illustrated in the Fig. 6), to convert the first down Cu-l~v.~ul- signal supplied thereto on line 210 into filtered, baseband signals. The internal circuitry which converts the first down ~Ull~ ;Oll signal into the baseband signals generates an in-5 phase signal, I, on line 218, and a signal in phase .~uaL~.Lulvtherewith, Q, on line 220 When antenna 180 receives a discrete, encoded signal, the I
and Q signals ~ on lines 218 and 220 are supplied to analog-to-digital ~ull, ~. t~ 222 and 224, ~ vi,l o~ _ly A~D cu , ~. ~v., 222 and 224 generate digital signals on lines 226 and 228, ~v ~ ly. For purposes of ill- ' ' - , three lines 226 and 228 connect each AID
converter 222 and 224 to digital signal processor 230 Digital signal processor 230, in the preferred Pmh~dirnPnt~
contains an ~lg~rithm to perform gain control filnrtinn~ and, - ~ ' -lly, an algorithm to perform the function of an equalizer.
Digital signal processor 230 generates output signals on lines 232 which are supplied to digital-to-analog converter 234. (Again, for purposes of ill, ' three lines 232 connect digital signal processor 230 to DtA converter 234). A/D ~;U~ t~D 222 and 224, digital signal processor 230, and D/A . u~ 234 may together form a single il~t~ circuit forming a DSP, illustrated by block 238, shown in hatch Digital signal processor 230 generates an output signal on line 242 iLL.,li~_ of the ;. ~ signal i ~ in ~ iP
, ~ 1 form to antenna 180 Digital signal processor 230 also - signals on lines 232 which are supplied to D/A converter 234. D/A converter 234 generates a signal on line 244 lV~UUll;~;~_ to the signal level of the signal received by antenna 180. The signal ~vllc.~t~ on line 244 may be utilized to control the signal levels of the signal received by the receiver which are lV,UlUdU~Vd on line 242.
When the signal ~læ ~ d to antenna 180 is a ~ull~.lL-.llal, ~....I.i,....~,r wave gignal, such as a conventional FM signal, circuitry internal to ZIF section 214 ~1Pmn~ tP~ the received signal and generates an audio signal on line 248 which is lV~ L~. of the 2~66711 .

i lrv. ' signal portion of the .. ~ signal received by antenna 180.
ZIF section 214 further contains circuitry internal thereto (not illustrated in the diagram of Fig. 6) for ~GLo.~.Lillg an output at AGC
5 output 252 i..d;~li~ of tbe signal level of a signal received by antenna 180.
Lines 244 and 252 ~ signals indicative of the signal levels of the signal received by antenna 180 when the signal is a TD~A .~ ;L~ m~d~ t~d il~l~liu~ signal ûr a conventional, 10 c~---/:..- ,, r- ~LV~ moc~ t~d ;~f~--...A~: -. signal, G.,~o~ GIy, are supplied to switch 256. Switch 266 may be c - .~ ;1 of a 2:1 . Switch 256 sllt~ t~ly couples line 244 to amplifier 209 on line 260, or line 252 to amplifier 209 on line 260. Switch 256 is actuated by a signal supplied thereto ûn line 264. In the preferred 15 ~ ~ho.l;~: -1. of the present invention, the cûntrol signal is supplied to the receiver by a lûgic section of the " ', ~ ~
When the signal supplied on 264 actuates switch 256 ~uch that line 252 is coupled to line 260, thereby . u. . .~ the AGC out of ZIF
section 214 to amplifier 209, the control signal ~ .1 internal to 20 ZIF section 214 is utilized to control the signal level of the signal rece*ed by the receiver. Alb . ..~l~ly, when the signal supplied on line 264 actuates svvitch 256 such that lina 244 is coupled to line 260, thereby C''""~ L the output of the digital signal processor 230 to amplifier 209, the control signal ~ LGd by the digital signal 25 processor 230 i~ utilized to control the signal levels of the signal received by the receiver.
Turning now to the flow diagram of Fig. 7, the method steps of the method of present invention are shov~n. The method of the present invention controls signal levels of a signal received by a 30 receiver. First, and as illustrated by decision block 400, the values of the signal levels of the signal received by the receiver when the signal is cu .~,;Ded of either a conventional, constant envelope signal or a non ~u.. c.L~IL envelopc signal are dG~ d.

206671~

When the f~ignal rece*ed by the receiver is a ~u ~ liu..hl constant envelope signal, a branch is taken to block 402, and a first gain control signal l~ UllD;~r to values of the signal levels of the signal received by the receiver when the signal is ~ ;F~I ûf u 5 constant envelope signal is ~r~ ~ Ne~t, and as illustrated by block 404, the ~ 9 Cl~ of the signal received by the receiver .~u..si~ to the first gain control signal are adJusted.
When the signal received by the receiver is a non-constant envelope signal, a branch is taken to block 406, and a second g~un 10 control signal 1 6~ Ull~ to values of the signal levels of the signal received by the receiver when the signal is ~.,...,.. ;~d of a non-constant envelope signal is ~. ~l~.l Ne~t, and as il11lP~--f~ted by block 408, the ~...~.1;1..~1~ ~L&~ .;P~;~; of the signal received by the receiver 16~ul~h~-3 to the second gfun control signal are adjusted.
While the present invention has been described in ~ u-~
with the preferred ~ ' of the various figL~res, it is to be od that other similar -.h~ may be used and m~ifi--~ n~ and additions may be made to the described I ..ho.l;... .l~l for p~.rO."~i..g the same function of the present 20 invention without deviating therefrom. I l,_.. fu~, the present invention should not be limited to any single ~ but rather ;. ' u2d in breadth and scope in accul dol~e with the recitation of the qpp-on~3~d claims.
What is claimed is:

Claims (18)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A gain control system for controlling signal levels of a signal received by a receiver, said gain control system comprising:
first down-conversion circuitry for converting the signal received by the receiver into a first down-converted signal of an intermediate frequency and ofsignal level magnitudes representative of signal level magnitudes of the signal received by the receiver;
variable amplifier circuitry coupled to receive the first down-converted signal generated by the first down-conversion circuitry, said variable amplifiercircuitry for generating an amplified signal of the intermediate frequency at anamplification level corresponding to a gain coefficient of the variable amplifier circuitry;
second down-conversion circuitry coupled to receive the amplified signal for converting the amplified signal of the intermediate frequency generated by said variable amplifier circuitry into a baseband signal of signal level magnitudes representative of signal level magnitudes of the signal received by the receiver;
first signal detection circuitry, coupled to receive the baseband signal generated by said second down-conversion circuitry having means for converting the baseband signal upward in frequency to form an upconverted signal, and means, coupled to receive the upconverted signal, for determining values of thesignal levels of the signal received by the receiver when said signal is comprised of a constant envelope signal and for generating a first gain control signal responsive to values of the signal levels determined thereat;
second signal detection circuitry, coupled to receive the baseband signal generated by said second down-conversion circuitry, for determining values of the signal levels of said signal received by the receiver when the signal is comprised of a non-constant envelope signal, the second signal detection circuitry formed thereby having, as a portion thereof, a digital signal processor, operative during times in which the signal received by the receiver is comprised of the non-constant envelope signal and non-operative during times in which the signal received by the receiver is comprised of the constant envelope signal, and for generating a second gain control signal responsive to values of the signal levels determined thereat; and means for alternately applying either the first gain control signal or the second gain control signal to the variable amplifier circuitry thereby to adjust the gain coefficient of the variable amplifier circuitry.

2. The gain control system of claim 1 wherein said means for applying comprises means forming a switch for applying either the first gain control signal or the second gain control signal to the variable amplifier circuitry.

3. The gain control system of claim 2 wherein said switch formed by the means for applying is actuated by a signal transmitted to the receiver.

4. The gain control system of claim 2 wherein said switch formed by the means for applying comprises a multiplexer.

5. The gain control system of claim 1 wherein said constant envelope signal comprises a frequency modulated signal.

6. The gain control system of claim 1 wherein said non-constant envelope signal comprises a composite modulated signal.

7. The gain control system of claim 1 wherein said second down-conversion circuitry for converting the amplified signal generated by the variable amplifier circuitry into the baseband signal comprises a zero intermediate frequency down-conversion section.

8. The gain control system of claim 7 wherein said zero intermediate frequency down-conversion section generates an analog output signal indicative of the signal received by the receiver.

9. The gain control system of claim 7 wherein said zero intermediate frequency down-conversion section generates a signal corresponding to in phase and quadrature components of the signal received by the receiver.

10. The gain control system of claim 9 wherein said digital signal processor of the second signal detection circuitry is coupled to receive the in phase and quadrature components, respectively, generated by the zero intermediate frequency down-conversion section.

11. The gain control system of claim 10 wherein the digital signal processor embodies an algorithm for calculating desired levels of the second gain control signal.

12. The gain control system of claim 10 wherein the digital signal processor further comprises a software equalizer.

13. The gain control system of claim 1 wherein said variable amplifier circuitry forms a portion of a zero intermediate filter.

14. The gain control system of claim 13 wherein either said first gain control signal or said second gain control signal is supplied to an input of thezero intermediate filter.

15. A dual mode transceiver operable to receive both a constant envelope modulated signal and a non-constant envelope modulated signal, said transceiver comprising:
first down-conversion circuitry for converting the signal received by the receiver into a first down-converted signal of an intermediate frequency and ofsignal level magnitudes representative of signal level magnitudes of the signal received by the receiver;
variable amplifier circuitry coupled to receive the first down-converted signal generated by the first down-conversion circuitry, said variable amplifiercircuitry for generating an amplified signal of the intermediate frequency at anamplification level corresponding to a gain coefficient of the variable amplifier circuitry;
second down-conversion circuitry, coupled to receive the amplified signal, for converting the amplified signal of the intermediate frequency generated by said variable amplifier circuitry into a baseband signal of signal level magnitudes representative of signal level magnitudes of the signal received by the receiver;
first signal detection circuitry, coupled to receive the baseband signal generated by said second down-conversion circuitry, having means for converting the baseband signal upward in frequency to form an upconverted signal, and means, coupled to receive the upconverted signal, for determining values of the signal levels of the signal received by the receiver when said signal is comprised of the constant envelope signal and for generating a first gain control signal responsive to values of the signal levels determined thereat;
second signal detection circuitry, coupled to receive the baseband signal generated by said second down-conversion circuitry, for determining values of the signal levels of said signal received by the receiver when the signal is comprised of the non-constant envelope signal, the second signal detection circuitry formed thereby having, as a portion thereof, a digital signal processor, operative during times in which the signal received by the receiver is comprisedof the non-constant envelope signal and non-operative during times in which the signal received by the receiver is comprised of the constant envelope signal, and for generating a second gain control signal responsive to values of the signal levels determined by the second signal detection circuitry; and a switch coupled to receive both the first gain control signal and the second gain control signal, and operative to apply the first gain control signal to the variable amplifier circuitry when the signal received by the receiver is comprised of the constant envelope signal and, alternately, to apply the second gain control signal to the variable amplifier circuitry when the signal received by the receiver is comprised of the non-constant envelope signal.

16. A method for controlling signal levels of a signal received by a receiver, said method comprising the steps of:
converting the signal received by the receiver into a first down-converted signal of an intermediate frequency and of signal level magnitudes representative of the signal level magnitudes of the signal received by the receiver;
applying the first down-converted signal to variable amplifier circuitry to generate thereby an amplified signal of the intermediate frequency at an amplification level corresponding to a gain coefficient of the variable amplifier circuitry;
converting the amplified signal of the intermediate frequency into a baseband signal of signal level magnitude representative of signal level magnitudes of the signal received by the receiver, when the signal received by the receiver is comprised of a constant envelope signal, converting the baseband signal upward in frequency to form an upconverted signal, and then determining values of the signal levels of the signal received by the receiver responsive to values of the upconverted signal;
generating a first gain control signal responsive to determined values of the signal levels of the signal received by the receiver when the signal is comprised of the constant envelope signal;
when the signal received by the receiver is comprised of a non-constant envelope signal, determining values of the signal levels of the signal received by the receiver responsive to values of the upconverted signal;
generating a second gain control signal only during times in which the signal received by the receiver comprises the non-constant envelope signal responsive to determined values of the signal levels of the signal received by the receiver; and adjusting the gain coefficient of the variable amplifier circuitry responsive to either the first gain control signal when the signal received by the receiver is comprised of the constant-envelope signal or the second gain control signal whenthe signal received by the receiver is comprised of the non-constant envelope signal.

17. The method of claim 16 wherein said constant envelope signal comprises a frequency modulated signal.

18. The method of claim 16 wherein said non-constant envelope signal comprises a composite modulated signal.