在這次研究中，提出以負壓產生器改善檢光二極體頻寬的想法，並且嘗試將 負壓產生器整合進 0.18μm 金氧半製程以實現一個 2Gb/s 的光接收器‧雖然整合 的部分因為雜訊影響而無法成功，但在光接收器以及負壓產生器的個別功能方 面，還是能夠正常的工作‧而負壓產生器輸出端造成的鏈波雜訊，經由模擬以及 量測結果得知此雜訊不會影響光接收器的靈敏度‧採用的檢光二極體面積為 70μm× 70μm，在 850nm 光波長下利用不同輸入光強度驗證直流迴圈的正確操 作，並且在不同檢光二極體逆偏條件下驗證高頻補償迴圈的功能‧效能方面，此 設計在誤碼率小於 10-12 的條件下量測出-9.8dBm 的靈敏度，而負壓產生器在 -9.8dBm 輸入光強度下產生-9V 的輸出負壓，功率效率為 17.6%‧整個晶片在 1.8V 供應電壓下消耗 90mW 的功率‧另外，在 2.5Gb/s 訊號速度下，可以量測 出-8dBm 的靈敏度，而負壓產生器也有-8V 的輸出負壓‧
另外，為了在量測上看出轉阻放大器的效能，我們利用開迴路(Open-Loop) 的方法，避開可變增益放大器對靈敏度的限制，因為可變增益放大器在提供較高 的低頻增益時會使頻寬過於衰減以致於影響到靈敏度的量測，因此利用開迴路將 可變增益放大器設定在不影響頻寬的條件下，進行 BER 的測試‧圖 5.1 為 BER 的測試結果，在開迴路的設定下，觀察 BER<10-9 的靈敏度，可以看到的是在 2Gb/s 的條件時靈敏度大約是-12.5dBm，這表示轉阻放大器在不受可變增益放 大器的影響時，靈敏度約可達到-12.5dBm‧而在 2.5Gb/s 的條件下則測得靈敏 度為-11dBm‧因此可變增益放大器在往後的設計上除了消耗功率的考量外，需 更加注意增益與頻寬的關係‧圖 5.2(a)(b)分別為 2Gb/s 及 2.5Gb/s 在-12.5dBm 及-11dBm 靈敏度下的輸出眼圖‧
圖 5.1 開迴路設定下的 BER 測試
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(a)2Gb/s, -12.5dBm, 6.7mV/div (b)2.5Gb/s, -11dBm, 6.7mV/div
圖 5.2 BER<10-9的開迴路輸出眼圖量測
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附錄
TIA in Main Path
Vbias Vbias
Vout
Vbias Vbias
Vout
Rfilter
Cfilter
71
S2D in Main Path
M1 M2
M3 M4
R1 R1
R2 R2
R3 R3
Vin
CF CF
Vout VDD
S2D in Dummy Path
M1 M2
M3 M4
R1 R1
R2 R2
R3 R3
Vout VDD
72
73
VGA in Main Path & Dummy Path
Vin
Slope controller
Isc
74
Error amplifier
Vin+ M1 M2
Vin-M4
M5 M6 M7
M8 M9
M10 M11
CL
Vout VDD
Buffer
Vi1 Vi2
Vout 50Ω
M1 M2 M4 M5
Rdc1 Rdc2
Cdc
VDD
50Ω
75
Non-overlapping clock generator
Delay
Delay CLK_in
Delay
Delay
Delay
Delay
CLK1
CLK2
CLK3
CLK4
DFF in Frequency divider
Din
clk clkb
clkb
clk clkb
clk
clk clkb
Q Qbar
clkb clk
Boosted Charge Transfer Block
Vi Vo
S1
S2
S1
S2
76
Hysteresis comparator
VREF M1 M2 Vin
VDD
Vout
M3 M4
M5 M6
M8 M9
M10 M11
CL
Ring Oscillator
CLK_out
Voltage Divider
VDD
R1 R2
R2 R2
7R2
VPD
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