ƶ!


߻ ϼ̴ٸ, ˾ƺ մϴ.

 

Stability factor, K

켱 ȸγ ý ܰ迡 ȸ Ȯϰ ľ ִ stability factor K ˾Ƶ ʿ䰡 ֽϴ.

 

K Ǹ Ǯ, ݻǴ Ǵ ֽϴ. K ڴ Ի 1 ݻ ǹϰ, и Ǵ Դϴ. ⼭ ߿ ǥ S12Դϴ. S12 (Ʈ2) Է(Ʈ1) ư ϴ ν, ᱹ feedback Ÿ ǥԴϴ. K ϱ⿣ , ᱹ feedback ȸδ Ҿ ִٴ ǹ̰ ˴ϴ. ׷ и feedback S12 Ŭ K ۾ ˴ϴ. ׸ feedback loop gain ߻ϴ ٷ K=1 Դϴ.

׷ ƽôٽ, K > 1 ̸ ȸδ Ǿ(unconditionally stable)ϰ, K < 1 ̸ Ǻ (conditionally stable)մϴ. K 1 stability circle ְ Ҿ ֽϴ. Ǵ K 1 ȳ ֽϴ. K < 1̶ ļ Ʒ (stability circle) ׷ Ǵ ãƾ մϴ.

: Input stability circle ũ

: Input stability circle ߽ǥ

: Output stability circle ũ

: Output stability circle ߽ǥ

 

K 1 Ǻ Ҿ ãƼ Ҿ  ļ Ǵ  ʵ ˴ϴ. ٸ ڰ ʹ Ҿؼ ̷ ιۿ 谡 ȵǴ 쿡 ̷ ؾ, ϸ  뿪 K > 1 ǵ ˴ϴ. ϸ Ҿ ҵ ϴ . K > 1 Ǹ ƿ ̽Ʈ ٱ з 鿩ٺ ʿ䵵 ϴ.

ư ļ뿪 K > 1 ǵ ȸθ ȭŰ Դϴ. ( K < 1 Ҿ ãƼ ˴ϴ)

 

ٽɿ

ϴ , ֽϴ. ٽѹ شϴ ׸ .

feedback loop ̼Ҿȣ ݺ gain 鼭 ̸ , װ . ׷ٸ loop θ ִ ֵ ȸθ Դϴ. Ǿƴϰ ߻ϴ loop ̹Ƿ, ̷ loop Ű ߿ ˴ϴ.

߻ loop, ׸  ҿ ?
ġä̰, ̵(gain) ̴ س մϴ. Ʒ ׸ !!!

gain ƸԴ, ս ִ 𰡰 loop߰ ġؾ մϴ. ׷ Ͽ lossy * gain 1 ۵ , ̼ȣ ̻ Ŀ ʰ ׾  Դϴ. ̷ gain gain ƸԴ lossy loop gain̶ θ, loop ȣ ᱹ 󸶳 Ŀ ۾° Ÿ ǹ̰ ˴ϴ. ̷ loop gain 1 ϰ ǵ ϱ , װ ̹ ߻ loop Դϴ.

׷ gain ̴ Ҷ..  ǹ ϰ ó? ʹ ?
ӵǴ оø Ͻ ֽϴ.

 

gain ̴ lossy ҷ ϱ? ٷ (resistor)Դϴ.

ƽôٽ ⿡ Ҹ lossy Դϴ. 帣 ᱹ аϸ Ű ϰ ˴ϴ.

а϶ ǹ̴ ȣ 忡 ũⰡ ۾ٴ ǹ̰ ˴ϴ. ᱹ ޸ ش ο óǴ ȣݿ ⸦ Ű ǰ, ̼ ȣ аϿ Ҹ ְ ˴ϴ. ᱹ ߰ ġ loop gain 1Ϸ ߸μ ֽϴ.

׷ٸ ̷ ׼ڸ Ȯ  ġ ޾ƾ ȿ ?
ũ 3 ֽϴ.

1) Է¿ /ķ ״ޱ

Էºο /ķ ϸ Īɵ , Ư LNA ϸ ȵǴ Դϴ. Է ߿ 쿡 ϱ ϴ. ĺٴ ȿ ϴ.

2) ¿ /ķ ״ޱ

ºο /ķ ϸ , ״ ƸԱ ԰ Power amp ϱ ϴ. ĺٴ ȿ ϴ.

3) ̾ ο ״ޱ

̾ Է¼ο ķ ϴ 츦 ø ˴ϴ. ̰ Ȥ µ а DZ⵵ ,  ϴ Դϴ.

̰ ̾ ο 󸶳 帣° ԰ Ǵ ˴ϴ.

1mA 帣 ̾ Է¼ο 10 ϸ  ɱ? ̶ ƴ , V = I * R ǰϿ 0.001 * 10 = 0.01V аϰ ߻մϴ.

0.01V ū аϰ ƴ϶ ü ȸμɿ ٸ ֽϴ. ׷ ̼ ȣ uV ߵ ɸ 찡 0.01V аϿ ɷ ڸ Ҹ ϰ ׿   ֽϴ. ̷ DC޿ ٸ 鼭, ͼ loop ٴϴ ̼ AC ȣ ū ְ Ǵ Դϴ.

BJT base ԷµǴ ̾ ׻ ȿ ֽϴ. BJT collector  ̾ mA̻ 帣⵵ ϱ ׻Կ Ǹ ؾմϴ. FET ƴ controlǴ ƮͶ, gate bias uA 帣 ׻ ſ ϴٴ ֽϴ.


ư loop loss ߽Ű Թ ȿԴϴ. ̾ / ׻Թ ص ġ ʱ ׷ ʽϴ. · صص غ ̹Ƿ ص ʿ ֽϴ.

 

Negative feedback (μȯ)

˷ ϳ ٷ negative feedback(μȯ)Դϴ. feedback̶ ½ȣ Է ǵư ϰ, negative feedback ׷ ȯ - Ǿ Է¿ ư մϴ. ٽøؼ սǿҸ Ͽ gain ߸ Ǵ ȯ negative feedback̶ Ҹϴ. սǿҰ  ϴ feedback̶ positive feedback̶ θ ˴ϴ. ư 鼭 loop gain Ǹ positive, ҵǸ negative θ .

Negative Feedback ȿ . ٽ Ǵ Tr ֱٹ濡 ġϱ Դϴ. ̷ negative feedback Ʒ ΰ ֽϴ.

1) Parallel negative feedback (ĺμȯ)

ôٽ Tr Է° ´ ϴ loop , װ ijн͸ Դϴ. ijн feedback θ DC ϸ ȵű DC blocking Դϴ. ֿ ϴ , Դϴ.

̰ Tr ֱٹ濡 feedback loop  ȣ Ȥϴ ϰ ˴ϴ. ᱹ Ȥ Ѿ ȣ ῡ loop Ÿ ٰ 鼭 ϰ ׾ϴ. Ȯ ¾ƴϰ ʿ, ϱ ڸ ̷ٴ . ^^;

Tr ȸο Բ ؼ ٸ, ̷ ȯ Trü loopƯ ü feedback Ư ȭŰ ˴ϴ. ⼭ loop װ K ö, ׷ ̵ ׻ ݴ ۾ٴ ؾ մϴ.

2) Series negative feedback (ĺμȯ)

RF BJT emitter Ȥ FET source Ѽ common emitter Ȥ common source ϴ 찡 ϴ. , emitter/source ̿ δ͸ ϴ 찡 ̰ ٷ series negative feedback̶ մϴ. δʹ DCԴ ׳ AC忡 ū Ǵ Դϴ. (Z = 2 f L ) ᱹ AC Ǵ ڰ Ե ε, ׸ ٽ ıȯó loop ƴ϶, ground Ÿ loop ״ ˴ϴ. ׷ ıȯ ϴ ̱.

ư Tr ¿ ߻ϴ Ground loop AC  Ǵ ÷Ǹ鼭 ̼ ȣ Ŀ Ȯ ׿ ϰ ˴ϴ. μȯ ȯ ~ ̵ ٿ ˴ϴ. ΰ ߿ Ư¡, ĺμȯ 뿪 Ǵ Ī ִ ִٴ Դϴ. 뿪 S11 ְ ,ᱹ ̰ ̾ϴ.

ڰ ϳ 뿪 ϰ ö ε, ̷ ȯ ̿ϸ 뿪 - ׿ν ᱹ ˴ϴ.

̷ ĺμȯ ̿Ͽ ̵ ̴ /Ī/ ϴ degeneration ̶ θϴ. ⼭ δʹſ ̳ ijн͸ ̿ , ȿ 鿡 δͰ ֿ˴ϴ.


ΰ negative feedback Ȳ ° Ǵ Դϴ. , ̷ negative feedback Tr ִ ִ gain ƸԴ ٴ Դϴ. K ( ) gain ϴ.

Negative feedback ̷ , S12 ҽŰ Դϴ. S12 (Ʈ2) Է(Ʈ1) 귯 ȣ ǹϸ, ᱹ ̰ Է ư feedback Īϴ Դϴ. ̷ S12 ҽŰ ʿ S21, ̵浵 پ ˴ϴ.

̰ ɵȸδ ̵ ݴ ϴ. ̵ ٴ loop󿡼 ȣ Ŀ ɼ ̰, ׷ ᱹ ü ̵ ߸ ˴ϴ. ׷ ̵ ū ļ ׻ K  .

Negative feedback ū R,L ڰ ȭѼ ̵ ߸ Ǵ ٴ Դϴ. ·ų ̵ ݴ 귯Ƿ trade off ʿϰ ˴ϴ.

 

н ijн (Bypass capacitor)

ijн (shunt capacitor) ȸο ſ ϰ ˴ϴ. Ư ϱ Բ ķ ijнͳ ܵ ޸ 찡 .

ijнʹ DC ϰ ļ ȣ ϰ ˴ϴ. ׸ ijнϽ Ŭ ļ AC(RF)ȣ ŵϴ. ׷Ƿ ķ ޸ ijнʹ, AC忡 Ground ٷ Ǿ short ó մϴ.

ܿ и ° ƴ϶, ȣ µǴ 쵵 ׷ ƾ մϴ. ׷  ޸ ijн͸ ACȣ Ǿ ׿ ˴ϴ. ׸ ſ ļ ߴ 찡 Ƽ ijнϽ Ŀ ˴ϴ. ׷ ſ ijнʹ uF ū źŻ ijнͰ ϰ Ǵ Դϴ.

̷ Ű "DC ´" ǥ մϴ. ϰ ; DCȣ 鸲 ּ شٴ ǹ. ᱹ ⸦ ϰ ִ Դϴ.

׸ ̷ ȸ Ե ó ۿϸ, ο ߻ Բ ȸ ϽŰ Ұ ˴ϴ. ׷ ؼ DC ֵ ̾ ο ķ н ijн͸ ڽϴ. н(bypass) AC Ѽ ڴٴ ǹ.

DC ̾ ο ݵ ̷ ijнͰ  ϳ̻ ޸ ϴ. ĸ ū ijнͿ, Ұ ִ Ư ļ ijн ΰ Բ Ǵ 찡 .

׸ , δ Ǵ /4 θ ̿Ͽ RF(AC)ȣ DC ̾ ԵǾ loop 鼭 Ͼ ʵ ݴϴ. Ϻ ʾƼ Ϻ ļ, Ư ϴ.

δͿ AC Ǵ ( Z = 2 f L ) غ ֽϴ. δͷ RF , Ŀ ǰϿ ļ δͰ ū AC ̱ Դϴ. Ǵ ũϱ RF , ȣ忡 ACװ ſ Ƽ   ִ . /4 ļ ܴ̿ ȿ ᱹ ٸ ļ ֽϴ.

׷ δͳ /4 RF choke Ŀ ̿ ݵ ijнͰ ־ߐ ְ Ǵ Դϴ. (̰ low pass trap : ̶ մϴ)

 

󿡼 ߻ϴ

ǰ , Ͼ 찡 մϴ. 󿡼 Ÿ ϰ ð ʵ Ϸ  ؾ ұ?

󿡼 Ÿٴ ǹ̴, DC ޱ ¿ ſ ֽϴ. 켱 ׶尡 ִ? ȯ ͼ ó ̰ Ǵ 찡 ϴ.  DUT ϴ ļ뿪 Ĺó ߱ ݸ ̸ ߰ϱ ϴ.

׷ ý  ʰ DC ޱ⸦ Ͽ ϴ 쿡 ׻ 뷮 źŻ ijн͸ е忡 ķ ص ʿ䰡 ֽϴ. ýۿ ʴ 󿡼̶ ؼ ʿմϴ. ̰ ٷ н ijн. ̰ ־ ⺻ Ŀ ϴ Դϴ.

п ǹ̳ ߵ ̶, ܼƮ ׶尡 ϵǾ ְ Ǿ Դϴ. ׷ 쵵 ̿Ͽ ϴ 찡 ϴ. ׶尡 ӵǴ Ư ͼ ߻ŵϴ. ȴµ Ƽ̳ ҷ  쵵 ֽϴ.

ư ߿ ̻ ڲ Ͼٸ, Ʈ м kHz ~ MHz 뿪 Ǵ Ȯ ʿ䰡 ֽϴ. IJ Ͼ DC ɾ 켱 ִ 뿪 Ⱦ.

󿡼 Ÿ ϰ ׳ ϴٺ 鸮 ϱ ġ ׿ ֽϴ. Ͼ ؾ κ Դϴ.

 

ȣ

߿ ϳ ٷ ȣ Դϴ. ȣ ̶, Power ampó ū ȣ ٷ ϴ ɵȸο Ư ¿ ߰ߵǴ Դϴ. DC ɾ ʰ, Ŀ鼭 ¿ ߰ߵǴ .

ϸ ̶ ٴ ǻ ٰ , ߻ 鿡 ϴ. ȣ ٷ Tr, ȣ̶ ȣ¿  ȭմϴ. ׷ ҽȣ ó K 1̻ ٰ, ü ϸ鼭 Ҿ Ÿ Ϻ feedback loop Ű⵵ մϴ.

̾ ׷ Ÿ մϴ. Ÿ ´뿡 ̵̳ 鸮 ϱ⿡ Ҿ ȸ̱ .  Ⱑ ~ ָմϴ. Ī ̾ ΰ δͿ ijн ؼ ƾ ϴµ, ȣ ںе̶ ̷ Ͼ ʵ ⵵ ʿ䰡 ֽϴ. ^^;

 

ƾ Ѵ!

ϸ, е ֽϴ. ⺻ 鿡 غҽϴٸ, RF Ͼ ϸ鼭 κ ذ˴ϴ. ׸ Ǽ ȸ , ý ߻ϴ ̶, ݵ DC ޴ IJ 캸 Ͻñ ٶϴ. ᱹ ī ü մϴ.

ε ֽϴ. ڻ° ų, PCB ° ڰų, Ī Ҿ ڰ ִٴ Ҿ ɼ ϱ Ͼ ϴ.

ָŸȣ ¿ ٰ ĵ,  ⺻ ' ִ' ؾ ϴ RF Ͼ Դϴ. Ʃؼ ϴ RF ־ ʼ ϳ ص ƴ .

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