BL1920 2.5Gbps Low Noise CMOS Optical Trans-Impedance Amplifier General Description The BL1920 is a low noise low power smart CMOS optical trans-impedance amplifier with single input and differential output. Received power monitoring and automatic gain control (AGC) are integrated. It is suitable for 2.5Gbps data rate operation with a high trans-impedance gain up to 87db to ensure good sensitivity. The BL1920 offers an internal regulator to bias the PIN photodiode, while for APD photodiode ROSA an external bias circuit is needed. A replica of the average photodiode current is available at the IMON pad for photo alignment and received power monitoring (SFF-8472 compliant). For optimum system performance, the BL1920 die should be mounted with a GaAs or InGaAs PIN photo-detector inside a focused TO-CAN or other optical sub-assembly. Features 195nARMS input referred noise at 2.1G bandwidth Standard CMOS process Typical 24kΩ differential trans-impedance Monitor output (SFF-8472 compliant) AGC provides dynamic range of 37dB Differential CML output Internal or external bias for photodiode (PIN photodiode, APD photodiode) Standard 3.3V supply Available in die form only Application Fields 2x Fiber Channel, EPON, GPON, PCI Express, ATM/SONET Block Diagram IMON Regulator PINC Regulator DC restore Low pass filter Phase splitter PINA Low pass filter VDD_TIA V1.0 Output buffer OUTP OUTN Swing detector AGC CEC – Shanghai Belling Co. Ltd. 1 BL1920 Ordering Information Part number Package Operating temperature BL1920 Wafer -40℃ to 85℃ Revision History V1.0 Revision Level Date Description A Preliminary August 2014 Internal Release http://www.belling.com.cn/ 2 BL1920 TABLE OF CONTENTS GENERAL DESCRIPTION .................................................................... 1 FEATURES.............................................................................................................................................................1 APPLICATION FIELDS ............................................................................................................................................1 BLOCK DIAGRAM .................................................................................................................................................1 ORDERING INFORMATION ................................................................. 2 REVISION HISTORY ............................................................................. 2 1.0 PRODUCT SPECIFICATION ............................................................ 4 1.1 ABSOLUTE MAXIMUM RATINGS.............................................................................................. 4 1.2 RECOMMENDED OPERATING CONDITIONS .............................................................................. 4 1.3 DC CHARACTERISTICS .......................................................................................................... 4 1.4 AC CHARACTERISTICS .......................................................................................................... 5 1.5 DYNAMIC CHARACTERISTICS ................................................................................................. 5 1.6 PAD INFORMATION ............................................................................................................... 6 2.0 APPLICATION INFORMATION ........................................................ 8 2.1 FUNCTIONAL DESCRIPTION .................................................................................................... 8 2.1.1 Main Trans-Impedance Amplifier (TIA) ............................................................................................ 8 2.1.2 Phase Splitter ....................................................................................................................................... 8 2.1.3 Automatic Gain Control (AGC).......................................................................................................... 8 2.1.4 Output Buffer........................................................................................................................................ 8 2.1.5 Received Power Monitor .................................................................................................................... 8 2.2 RECOMMENDED CONNECTION ................................................................................................ 9 2.2.1 Selecting the Monitor Resistor.......................................................................................................... 9 2.2.2 Treatment of PINC ............................................................................................................................... 9 2.3 TO-CAN LAYOUT .................................................................................................................. 9 V1.0 http://www.belling.com.cn/ 3 BL1920 1.0 Product Specification 1.1 Absolute Maximum Ratings Device can fail or be damaged by operating beyond these limits. Table 1-1 Absolute Maximum Ratings Symbol Parameter Rating Units VCC Supply Voltage (VCC-GND) -0.4 to 4 V Tsto Storage Temperature -65 to 150 ℃ Tjun Junction temperature -40 to 125 ℃ Iin PINA input current 0 to 3 mApp VPINA Input voltage at PINA -0.4 to 2 V IPINC Maximum average current sourced out of PINC 6 mA VPINC, VMON Input voltage at PINC and IMON (1kOhm load) -0.4 to VCC+0.4 V VOUT Maximum output voltage at OUTP and OUTN 0 to VCC V HBM MODE ESD 2 KV (1) ESD Note: 1: PINA has no ESD protection and thus, make sure that ESD voltage at pin PINA never exceeds 500V. 1.2 Recommended Operating Conditions Table 1-2. Recommended Operating Conditions Symbol Parameter Rating Units VCC Supply Voltage (VCC-GND) 3.3 ± 10% V CPD Max. photodiode capacitance 0.5 pF TA Operating ambient temperature -40 to 85 ℃ 1.3 DC Characteristics All parameters are characterized under recommended operating condition. Typical specifications are for VCC = 3.3V, TA = 27°C, CPD = 0.3pF, unless otherwise noted. Table 1-3. DC Characteristics Symbol Parameter VPINC Internal regulator output voltage for PIN photodiode cathode bias internally 2.5 V VPINA Photodiode anode bias voltage 0.8 V ICC Supply current V1.0 Min 28 http://www.belling.com.cn/ Typ 34 Max 41 Units mA 4 BL1920 Rout(diff) Differential output resistor Ω 100 1.4 AC Characteristics All parameters are characterized under recommended operating condition. Typical specifications are for VCC = 3.3V, TA = 27°C, CPD = 0.3pF, unless otherwise noted. Table 1-4 AC Characteristics Symbol Parameter Condition Min. Typ. Max. LFC Low frequency cutoff AGC non lick-in 35 KHz Voutp_p Peak to peak differential output voltage 100Ω differential load 320 mV DCD Duty cycle distortion 2.125Gbps 50 2.5Gbps 60 ps 7 Deterministic Jitter ( include DCD ) DJ PDJ In_rms 2.125Gbps, 2 – 1 PRBS 60 23 70 ps 2.5Gbps, 2 2.125Gbps, 2 – 1 PRBS 29 23 34 ps 2.5Gbps, 2 Minimum input optical (2) sensitivity Imon_off Monitor output offset Imon_erro r Monitor output accuracy – 1 PRBS 100k to 2.1GHz, Cin = 0.5pf (1) PIN_mean _min – 1 PRBS 7 Pattern dependant jitter (at crossing point) without DCD Input referred noise Units 2.5Gbps, BER < 10 -10 195 nA -27.7 dBm VMON = 0 to 2V 2 uA ±1. 5 dB Note: 1. 2.1GHz bandwidth Bessel LPF at the output terminal and 0.5pF capacitance at input. 2. At stated data rate and BER. Responsivity = 0.9 A/W, Extinction Ratio = 10, suppose PD capacitance = 0.5pF 1.5 Dynamic Characteristics All parameters are characterized under recommended operating condition. Typical specifications are for VCC = 3.3V, TA = 27°C, CPD = 0.3pF, unless otherwise noted. Table 1-5 Symbol Parameter G Trans-impedance (differential) BW -3dB bandwidth, Cin = 0.3pF τ AGC IAGC V1.0 Dynamic Characteristics Min Typ Max KΩ 24 1.62 1.94 Units 2.23 GHz AGC loop time constant 15 us AGC threshold 40 uApp http://www.belling.com.cn/ 5 BL1920 IOVL Input overload current 3 mApp Power supply rejection 1MegHz<f<30MegHz 30 dB Power supply rejection, f < 1MHz 40 dB PSRR 1.6 PAD Information Figure 1-6 BL1920 Pin Assignment 15 14 13 11 12 1 10 2 9 I30V10 201412 3 Table 1-6 4 5 6 7 8 BL1920 Pin Definitions Pin No. Pin Name 1 PINC Common PIN input. Connect to photo diode cathode and a 470pF capacitor to GND. 2 PINA Active PIN input. Connect to photo diode anode. 3 VCC Positive power supply. 4 IMON Analog current source output. A replica of average photodiode current. 5 NC -- 6 NC -- 7 NC -- 8 GND Ground pin. 9 VON Negative data output pin. 10 VOP Positive data output pin. 11 GND Ground pin. 12 AGC Monitor or force AGC voltage. V1.0 Description http://www.belling.com.cn/ 6 BL1920 13 NC 14 VDD_TIA 15 VCC V1.0 -Internal regulator output voltage for the main TIA power supply. Positive power supply. http://www.belling.com.cn/ 7 BL1920 2.0 Application Information 2.1 Functional Description The BL1920 is a CMOS trans-impedance amplifier with single input and differential output. It consists of a main TIA block, a phase splitter for single to differential ended signaling, AGC for trans-impedance control, an output buffer, and a received power monitor. The PINA pin gets the input photodiode current and the OUTP/OUTN pins get the differential output voltage. 2.1.1 Main Trans-Impedance Amplifier (TIA) The TIA consists of a high gain single-ended amplifier and a feedback resistor. Virtually all of the input current passes through the feedback resistor defining the voltage at the output. An on-chip low dropout regulator is designed for TIA to give excellent noise rejection up to several MHz. Higher frequency power supply noise is removed by the external decoupling capacitor. 2.1.2 Phase Splitter The phase splitter is designed to convert the single ended signal into differential ended signal. It consists of a high speed differential amplifier and a feedback circuit that serves as an active low pass filter (shown in figure 2-1-2). The whole loop is self-biased and then, a DC value is obtained as the common voltage of outp and outn. Their AC signals are filtered and the cut-off frequency is about tens of KHz, which makes the output signals keep differential. Figure 2-1-2 Phase splitter Block Diagram Opa Low pass filter outp Amp inp outn 2.1.3 Automatic Gain Control (AGC) The dynamic range of input current is 10uA-1mA, which requires a changeable trans-impedance to ensure that the TIA works properly. If the input current is large, the trans-impedance is supposed to be decreased so that the TIA operates in linear region. A MOS transistor in the triode region is used as a “voltage controlled resistor” to achieve the transimpedance variation. The AGC circuit changes the voltage of the MOS transistor corresponding to the input current. In the BL1920, the AGC only operates on signals greater than 50uA. When “signal detect” function is set in the following post amplifier, the knee in the gain response is important. It also aids in active photodiode alignment. The AGC pad allows the AGC control voltage to be monitored or controlled externally. 2.1.4 Output Buffer The power supply of the chip is 3.3V, which is not suitable for the phase splitter. So, the output buffer is needed to shift the output signals of the phase splitter to compliant with 3.3V supply. The output buffer is designed to drive differential 100Ω load with the CML output format. 2.1.5 Received Power Monitor This block monitors the average photodiode current through a high impedance current source. The output is compatible with the DDMI Received Power Specification (SFF-8472). Meanwhile, the block also contains a DC restore function in order that the core TIA works properly. The voltage on the IMON pad is in the range of 0 to 2.5V. V1.0 http://www.belling.com.cn/ 8 BL1920 2.2 Recommended connection When PIN photodiode is used, the anode of the photodiode is connected to the input of the TIA and the cathode is connected to AC ground, such as PINC terminal with decoupling capacitor. Reverse DC bias is applied to reduce the photodiode capacitance. Avalanche photodiode can be biased externally to a higher voltage. Figure 2-2-1. Internal PIN Bias GND VCC VCC(3.3V) C2=1nF PINC OUTP C1=470P Limiting Amplifier BL1920 PIN OUTN IMON PINA Rm=1K Figure 2-2-2. External APD Bias VCC Rb=500 GND VCC(3.3V) VPD(20-40V) C2=1nF PINC OUTP Limiting Amplifier BL1920 APD IMON OUTN PINA Rm=1K 2.2.1 Selecting the Monitor Resistor The monitor output sources a replica average photodiode current for monitoring purpose. An external resistor is connected to this pad to convert the current to a voltage. The voltage is in the range of 0 to 2.5V, requiring the resistor value to be set according to the input current. A typical value is set to be 1kOhm. 2.2.2 Treatment of PINC PINK requires bypassing to ground with a 470 pF capacitor when biasing a photo diode. If PINK is not used to bias the photo diode, it is not necessary to bypass. 2.3 TO-Can Layout Ball bonding is recommended with a 1 mil gold wire. For performance reasons the PINA pad is smaller than the others and also have less via material connected to it. It requires more care in setting of the bonding parameters. For the same reason PINA has not ESD protection. V1.0 http://www.belling.com.cn/ 9 BL1920 Figure 2-3-1 Typical Layout Diagram with Photodiode Mounted on TO-Can OUTN LOGO OUTP CAP Photodiode VCC IMON CAP Figure 2-3-2 BL1920 PAD Coordinates Coordinates Pin No. 15 14 13 11 12 1 10 2 9 I30V10 201412 3 Table 2-3-2 V1.0 4 5 6 Name 7 8 X Y 1 PINC -398 68 2 PINA -398 -68 3 VCC -232 -398 4 IMON -122 -398 5 NC -41 -398 6 NC 40 -398 7 NC 121 -398 8 GND 232 -398 9 VON 398 -67 10 VOP 398 67 11 GND 233 398 12 AGC 101 398 13 NC 0 398 14 VDD_TIA -101 398 15 VCC -231 398 BL1920 PAD Coordinates http://www.belling.com.cn/ 10