低噪声高单位增益带宽双极型运放设计

Design of a Low Noise and High Unity-Gain-Bandwidth Bipolar Operational Amplifier

设计了一款低噪声、高单位增益带宽的运放电路。该款电路基于0.25μm SiGe双极工艺,采用三级级联的形式,输入级选取多个双极型晶体管(BJT)并联,用作差分对管,以抑制噪声;中间级不但用pnp型BJT镜像电流源作为有源负载,而且并联多个横向pnp型BJT用以提升单位增益带宽;输出级则设计成低电容输入和低电容输出方式,借此拓展带宽。对所设计的运放电路进行了PSPICE仿真及硬件电路实验。结果表明,当电源电压为2.5 V时,运放电路的实测交流开环电压增益为80 dB,开环相位裕度为61.5°,单位增益带宽为203 MHz,在10 kHz处的输入电压噪声密度仅为1.2 nV/Hz^(1/Hz),因而可用于低噪声、高单位增益带宽的片上相位噪声测量电路和微波功率传感器等系统的设计中。

An improved operational amplifier with low noise, high unity-gain bandwidth was designed using 0.25 μm SiGe bipolar technology and was connected by three stages. Its input stage with multiple parallel bipolar transistor （BJT） connection was as a differential pair for low noise behavior. To broaden the unity-gain bandwidth, its intermediate stage, active loads consisted of pnp current mirror transistors and multiple lateral pnp transistors in parallel were used. To improve high frequency performances and enhance bandwidth, its output stage, low capacitance input and low capacitance output were adopted. PSPICE simulation and hardware experiment results show that AC voltage open-loop gain is 80 dB, open-loop phase margin is 61.5°, and unity-gain-bandwidth is 203 MHz when the supply voltage is 2.5 V. When the frequency is at 10 kHz, the input voltage noise density of the designed operational amplifier is only 1.2 nV/√Hz, so it can be used for low-noise and unity-gain-bandwidth on-chip phase-noise measurement or the systems of microwave power sensor circuit.