目前生醫電子感測電路主要分為穿戴式和植入式，生醫電子使用的感測電路大部分須要使用數年之久，故其中的放大晶片需要採用超低功耗設計才能保持整體電路的續航力同時也可大大降低晶片的發熱量。 目前應用於超低功耗無線傳輸接收解調晶片之調變方式有以下三種，從最早期的振幅鍵移調變（Amplitude Shift Keying, ASK）到最近被廣泛使用的頻率鍵移調變（Frequency Shift Keying, FSK）及本篇論文使用的相位偏移調變（Phase Shift Keying, PSK）。ASK將資料放在載波頻率之振幅上，藉由接收到之訊號振幅大小來解調回傳輸端之輸出資料。FSK則是將訊號分為不同頻率，經由接收電路解調還原傳輸端之資料。而PSK是一種利用相位差異的訊號來傳送資料的調變方式。抗雜訊能力是三種調變中最佳的，在傳送過程中即使嚴重失真，在解調時仍可盡量避免錯誤的判斷。 QPSK(Quadrature Phase-shift Keying)相較於PSK系列中最簡單的BPSK(Binary Phase-shift Keying)，QPSK在系統帶寬不變的情況下可以增大一倍數據傳輸速率或者在BPSK數據傳輸速率不變的情況下將所需帶寬減半。本架構是使用四個相位各差90°的訊號表示邏輯”00”、邏輯”01”、邏輯”10”及邏輯”11”的資料。它分別位在平面座標軸的X軸和Y軸上。這種系統在PSK系列中抗雜訊能力（SNR）是最佳的，在傳送過程中即使嚴重失真，在解調時仍可盡量避免錯誤的判斷。 本架構之QPSK發射器主要是由鎖相迴路、除頻器、相位選擇器所組成，鎖相迴路鎖住一穩定頻率，經過除頻器提供四個相位各相差九十度的訊號，等同於平面座標軸的四個相位，X軸和Y軸再分別經過相位選擇器選擇正向或反向訊號，便能產生位於零度、九十度、一百八十度及兩百七十度的訊號發射出去。 本論文的發射電路輸入參考訊號為8MHz、輸出的四個相位皆為64MHz，總功耗為3.66mW。在不同傳輸速率之間皆可正常運作，每bit在最差情況下2 Mb/s時會消耗1.83 nJ，但在16 Mb/s則只會消耗0.21 nJ。 Recently, wearable and implantable biomedical electronic devices are required urgently by biomedical applications. Biomedical information transmission between the devices can be achieved by wireless techniques. For extending life time of the devices, an ultra-low power and reliable wireless transmission interface is required. In this thesis, an ultra-low power (ULP), multi-rate, human body communication (HBC), quadrature phase-shift keying (QPSK) transmitter applied for wearable or implantable biomedical devices is proposed. Instead of adopting amplitude shift keying (ASK) modulation, QPSK modulation has better immunity against interferers and higher data rate as the same frequency bandwidth is used. But QPSK modulation usually leads to a higher hardware complexity and power consumption. In this thesis, a ultra-low power and low hardware complexity QPSK transmitter is proposed. The transmitter transmits QPSK modulated data at a carrier frequency of 64 MHz. As applied for wearable or implantable biomedical electronic devices, the transmitter consumes 3.66 mW under a minimum data rate of 2 Mb/s as designing in UMC 0.18 um CMOS process. The maximum energy consumption per transmitted bit is 1.83 nJ/bit. But under a maximum data rate of 16 Mb/s, the minimum energy consumption per transmitted bit is only 0.21 nJ/bit.
