VCA2612Y-1/2K

VCA VCA2612 261 2 SBOS117C – SEPTEMBER 2000 – REVISED APRIL 2004 Dual, VARIABLE GAIN AMPLIFIER with Low Noise Preamp FEATURES DESCRIPTION ● LOW NOISE PREAMP: • Low Input Noise: 1.25nV/√Hz • Active Termination Noise Reduction • Switchable Termination Value • 80MHz Bandwidth • 5dB to 25dB Gain Range • Differential Input /Output ● LOW NOISE VARIABLE GAIN AMPLIFIER: • Low Noise VCA: 3.3nV/√Hz, Differential Programming Optimizes Noise Figure • 24dB to 45dB Gain • 40MHz Bandwidth • Differential Input /Output ● LOW CROSSTALK: 52dB at Max Gain, 5MHz ● HIGH-SPEED VARIABLE GAIN ADJUST ● SWITCHABLE EXTERNAL PROCESSING The VCA2612 is a highly integrated, dual receive channel, signal processing subsystem. Each channel of the product consists of a low noise preamplifier (LNP) and a Variable Gain Amplifier (VGA). The LNP circuit provides the necessary connections to implement Active Termination (AT), a method of cable termination which results in up to 4.6dB noise figure improvement. Different cable termination characteristics can be accommodated by utilizing the VCA2612’s switchable LNA feedback pins. The LNP has the ability to accept both differential and single-ended inputs, and generates a differential output signal. The LNP provides strappable gains of 5dB, 17dB, 22dB, and 25dB. The output of the LNP can be accessed externally for further signal processing, or fed directly into the VGA. The VCA2612’s VGA section consists of two parts: the Voltage Controlled Attenuator (VCA) and the Programmable Gain Amplifier (PGA). The gain and gain range of the PGA can be digitally programmed. The combination of these two programmable elements results in a variable gain ranging from 0dB up to a maximum gain as defined by the user through external connections. The output of the VGA can be used in either a single-ended or differential mode to drive high-performance Analog-to-Digital (A/D) converters. APPLICATIONS ● ULTRASOUND SYSTEMS ● WIRELESS RECEIVERS ● TEST EQUIPMENT The VCA2612 also features low crosstalk and outstanding distortion performance. The combination of low noise and gain range programmability make the VCA2612 a versatile building block in a number of applications where noise performance is critical. The VCA2612 is available in a TQFP-48 package. Maximum Gain Select FBSWCNTL LNPOUTN VCAINN VCACNTL MGS1 MGS2 MGS3 RF2 SWFB RF1 FB VCA2612 (1 of 2 Channels) Analog Control Maximum Gain Select Voltage Controlled Attenuator Programmable Gain Amplifier 24 to 45dB CF Input CC LNPINP LNP Gain Set VCAOUTN LNPGS1 LNPGS2 Low Noise Preamp 5dB to 25dB LNPGS3 VCAOUTP LNPINN LNPOUTP VCAINP SEL Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. All trademarks are the property of their respective owners. PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. Copyright © 2000-2004, Texas Instruments Incorporated www.ti.com ABSOLUTE MAXIMUM RATINGS(1) Power Supply (+VS) ............................................................................. +6V Analog Input ............................................................. –0.3V to (+VS + 0.3V) Logic Input ............................................................... –0.3V to (+VS + 0.3V) Case Temperature ......................................................................... +100°C Junction Temperature .................................................................... +150°C Storage Temperature ...................................................... –40°C to +150°C NOTE: (1) Stresses above these ratings may cause permanent damage. Exposure to absolute maximum conditions for extended periods may degrade device reliability. ELECTROSTATIC DISCHARGE SENSITIVITY This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage. ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications. PACKAGE/ORDERING INFORMATION(1) PRODUCT PACKAGE-LEAD PACKAGE DESIGNATOR PACKAGE MARKING ORDERING NUMBER TRANSPORT MEDIA, QUANTITY VCA2612Y TQFP-48 PFB VCA2612Y " " " " VCA2612Y/250 VCA2612Y/2K Tape and Reel, 250 Tape and Reel, 2000 NOTE: (1) For the most current package and ordering information, see the Package Option Addendum located at the end of this data sheet. ELECTRICAL CHARACTERISTICS At TA = +25°C, VDDA = VDDB = VDDR = +5V, load resistance = 500Ω on each output to ground, MGS = 011, LNP = 22dB and fIN = 5MHz, unless otherwise noted. The input to the preamp (LNP) is single-ended, and the output from the VCA is single-ended unless otherwise noted. VCA2612Y PARAMETER PREAMPLIFIER Input Resistance Input Capacitance Input Bias Current CMRR Maximum Input Voltage Input Voltage Noise(1) Input Current Noise Noise Figure, RS = 75Ω, RIN = 75Ω(1) Bandwidth CONDITIONS f = 1MHz, VCACNTL = 0.2V Preamp Gain = +5dB Preamp Gain = +25dB Preamp Gain = +5dB Preamp Gain = +25dB Independent of Gain RF = 550Ω, Preamp Gain = 22dB, PGA Gain = 39dB Gain = 22dB PROGRAMMABLE VARIABLE GAIN AMPLIFIER Peak Input Voltage Differential –3dB Bandwidth Slew Rate Output Signal Range RL ≥ 500Ω Each Side to Ground Output Impedance f = 5MHz Output Short-Circuit Current Third Harmonic Distortion f = 5MHz, VOUT = 1VPP, VCACNTL = 3.0V Second Harmonic Distortion f = 5MHz, VOUT = 1VPP, VCACNTL = 3.0V IMD, Two-Tone VOUT = 2VPP, f = 1MHz VOUT = 2VPP, f = 10MHz 1dB Compression Point f = 5MHz, Output Referred, Differential Crosstalk VOUT = 1VPP, f = 1MHz, Max Gain Both Channels Group Delay Variation 1MHz < f < 10MHz, Full Gain Range DC Output Level, VIN = 0 ACCURACY Gain Slope Gain Error Output Offset Voltage Total Gain GAIN CONTROL INTERFACE Input Voltage (VCACNTL) Range Input Resistance Response Time POWER SUPPLY Operating Temperature Range Specified Operating Range Power Dissipation Thermal Resistance, θJA MIN –45 –45 TYP MAX 600 15 1 50 1 112 3.5 1.25 0.35 6.2 kΩ pF nA dB VPP mVPP nV/√Hz nV/√Hz pA/√Hz dB 80 MHz 2 40 300 2 1 ±40 –71 –63 –80 –80 6 68 ±2 2.5 VPP MHz V/µs VPP Ω mA dBc dBc dBc dBc VPP dB ns V 10.9 VCACNTL = 0.2V VCACNTL = 3.0V 18 47 –40 4.75 Operating, Both Channels TQFP-48 ±50 21 50 ±1(2) 24 53 0.2 to 3.0 1 0.2 45dB Gain Change, MGS = 111 UNITS 5.0 410 56.5 dB/V dB mV dB dB V MΩ µs +85 5.25 495 °C V mW °C/W NOTE: (1) For preamp driving VGA. (2) Referenced to best fit dB-linear curve. 2 VCA2612 www.ti.com SBOS117C MGS1 MGS2 MGS3 VCAOUTPB VCAOUTNB GNDB 46 VCACNTL VCAOUTPA 47 FBSWCNTL VCAOUTNA 48 VCAINSEL GNDA PIN CONFIGURATION 45 44 43 42 41 40 39 38 37 VDDA 1 36 VDDB NC 2 35 NC NC 3 34 NC VCAINNA 4 33 VCAINNB 32 VCAINPB VCAINPA 5 LNPOUTNA 6 LNPOUTPA 7 30 LNPOUTPB SWFBA 8 29 SWFBB FBA 9 28 FBB 31 LNPOUTNB VCA2612 18 19 VBIAS VCM 20 21 22 23 24 LNPGS3B 17 LNPGS2B 16 LNPGS1B 15 GNDR 14 LNPINPB 13 VDDR 25 LNPINNB LNPINPA LNPINNA 12 LNPGS1A 26 COMP2B LNPGS3A 27 COMP1B COMP2A 11 LNPGS2A COMP1A 10 PIN DESCRIPTIONS PIN DESIGNATOR 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 VDDA NC NC VCAINNA VCAINPA LNPOUTNA LNPOUTPA SWFBA FBA COMP1A COMP2A LNPINNA LNPGS3A LNPGS2A LNPGS1A LNPINPA VDDR VBIAS VCM GNDR LNPINPB LNPGS1B LNPGS2B LNPGS3B DESCRIPTION PIN DESIGNATOR Channel A +Supply (+5V) Do Not Connect Do Not Connect Channel A VCA Negative Input Channel A VCA Positive Input Channel A LNP Negative Output Channel A LNP Positive Output Channel A Switched Feedback Output Channel A Feedback Output Channel A Frequency Compensation 1 Channel A Frequency Compensation 2 Channel A LNP Inverting Input Channel A LNP Gain Strap 3 Channel A LNP Gain Strap 2 Channel A LNP Gain Strap 1 Channel A LNP Noninverting Input +Supply for Internal Reference (+5V) 0.01µF Bypass to Ground 0.01µF Bypass to Ground Ground for Internal Reference Channel B LNP Noninverting Input Channel B LNP Gain Strap 1 Channel B LNP Gain Strap 2 Channel B LNP Gain Strap 3 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 LNPINNB COMP2B COMP1B FBB SWFBB LNPOUTPB LNPOUTNB VCAINPB VCAINNB NC NC VDDB GNDB VCAOUTNB VCAOUTPB MGS3 MGS2 MGS1 VCACNTL VCAINSEL FBSWCNTL VCAOUTPA VCAOUTNA GNDA VCA2612 SBOS117C www.ti.com DESCRIPTION Channel B LNP Inverting Input Channel B Frequency Compensation 2 Channel B Frequency Compensation 1 Channel B Feedback Output Channel B Switched Feedback Output Channel B LNP Positive Output Channel B LNP Negative Output Channel B VCA Positive Input Channel B VCA Negative Input Do Not Connect Do Not Connect Channel B +Analog Supply (+5V) Channel B Analog Ground Channel B VCA Negative Output Channel B VCA Positive Output Maximum Gain Select 3 (LSB) Maximum Gain Select 2 Maximum Gain Select 1 (MSB) VCA Control Voltage VCA Input Select, HI = External Feedback Switch Control: HI = ON Channel A VCA Positive Output Channel A VCA Negative Output Channel A Analog Ground 3 TYPICAL CHARACTERISTICS At TA = +25°C, VDDA = VDDB = VDDR = +5V, load resistance = 500Ω on each output to ground, MGS = 011, LNP = 22dB and fIN = 5MHz, unless otherwise noted. The input to the preamp (LNP) is single-ended, and the output from the VCA is single-ended unless otherwise noted. This results in a 6dB reduction in signal amplitude compared to differential operation. GAIN ERROR vs TEMPERATURE GAIN vs VCACNTL 65 2.0 MGS = 111 60 55 1.0 45 MGS = 100 40 35 MGS = 011 30 Gain Error (dB) MGS = 101 50 Gain (dB) 1.5 MGS = 110 MGS = 001 20 0 –0.5 +85°C –1.5 MGS = 000 15 +25°C 0.5 –1.0 MGS = 010 25 –2.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 VCACNTL (V) VCACNTL (V) GAIN ERROR vs VCACNTL GAIN ERROR vs VCACNTL 2.0 2.0 1.5 1.5 1MHz 1.0 1.0 10MHz 0.5 Gain Error (dB) Gain Error (dB) –40°C 0 –0.5 5MHz MGS = 000 MGS = 011 0.5 0 –0.5 –1.0 –1.0 –1.5 –1.5 MGS = 111 –2.0 –2.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 VCACNTL (V) VCACNTL (V) GAIN MATCH: CHA to CHB, VCACNTL = 0.2V 100 90 90 80 80 70 70 60 60 Units Units 100 50 40 30 30 20 20 10 10 0 –0.5 –0.4 –0.3 –0.2 –0.1 0.0 0.1 0.2 0.3 0.4 0.5 –0.5 –0.4 –0.3 –0.2 –0.1 0.0 Delta Gain (dB) 4 50 40 0 GAIN MATCH: CHA to CHB, VCACNTL = 3.0V 0.1 0.2 0.3 0.4 0.5 Delta Gain (dB) VCA2612 www.ti.com SBOS117C TYPICAL CHARACTERISTICS (Cont.) At TA = +25°C, VDDA = VDDB = VDDR = +5V, load resistance = 500Ω on each output to ground, MGS = 011, LNP = 22dB and fIN = 5MHz, unless otherwise noted. The input to the preamp (LNP) is single-ended, and the output from the VCA is single-ended unless otherwise noted. This results in a 6dB reduction in signal amplitude compared to differential operation. GAIN vs FREQUENCY (VCA and PGA, VCACNTL = 0.2V) GAIN vs FREQUENCY (Pre-Amp) 30 5.0 LNP = 25dB 25 3.0 2.0 Gain (dB) 20 Gain (dB) MGS = 111 MGS = 100 MGS = 011 MGS = 000 4.0 LNP = 22dB 15 LNP = 17dB 10 1.0 0.0 –1.0 –2.0 –3.0 5 –4.0 LNP = 5dB 0 0.1 –5.0 1 10 0.1 100 1 10 Frequency (MHz) Frequency (MHz) GAIN vs FREQUENCY (VCA and PGA, VCACNTL = 3.0V) GAIN vs FREQUENCY (VCACNTL = 3.0V) 45 60 LNP = 25dB MGS = 111 40 LNP = 22dB 50 35 MGS = 100 30 40 Gain (dB) Gain (dB) 100 25 MGS = 011 20 15 LNP = 17dB 30 LNP = 5dB 20 MGS = 000 10 10 5 0 0 0.1 1 10 100 0.1 1 Frequency (MHz) GAIN vs FREQUENCY (LNP = 22dB) 100 OUTPUT REFERRED NOISE vs VCACNTL 1800 60 VCACNTL = 3.0V 1600 RS= 50Ω MGS = 111 50 1400 Noise (nV/√Hz) VCACNTL = 1.6V 40 Gain (dB) 10 Frequency (MHz) 30 20 1200 1000 800 600 MGS = 011 400 10 200 VCACNTL = 0.2V 0 0 0.1 1 10 0 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 100 VCACNTL (V) Frequency (MHz) VCA2612 SBOS117C www.ti.com 5 TYPICAL CHARACTERISTICS (Cont.) At TA = +25°C, VDDA = VDDB = VDDR = +5V, load resistance = 500Ω on each output to ground, MGS = 011, LNP = 22dB and fIN = 5MHz, unless otherwise noted. The input to the preamp (LNP) is single-ended, and the output from the VCA is single-ended unless otherwise noted. This results in a 6dB reduction in signal amplitude compared to differential operation. INPUT REFERRED NOISE vs VCACNTL 24 22 RS= 50Ω 20 18 16 MGS = 111 Noise (nV√Hz Noise (nV/√Hz) INPUT REFERRED NOISE vs RS 10.0 14 12 10 8 6 4 2 1.0 MGS = 011 0 0.1 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 1 10 VCACNTL (V) 100 1000 RS (Ω) NOISE FIGURE vs RS (VCACNTL = 3.0V) 11 NOISE FIGURE vs VCACNTL 30 10 25 8 Noise Figure (dB) Noise Figure (dB) 9 7 6 5 4 3 2 20 15 10 5 1 0 0 10 –45 100 1000 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 RS (Ω) VCACNTL (V) LNP vs FREQUENCY (Differential, 2VPP) LNP vs FREQUENCY (Single-Ended, 1VPP) –45 –50 Harmonic Distortion (dBc) Harmonic Distortion (dBc) –50 –55 3rd Harmonic –60 –65 –70 –75 –55 2nd Harmonic –60 –65 –70 –75 3rd Harmonic 2nd Harmonic –80 –80 0.1 1 10 100 0.1 Frequency (MHz) 6 1 10 100 Frequency (MHz) VCA2612 www.ti.com SBOS117C TYPICAL CHARACTERISTICS (Cont.) At TA = +25°C, VDDA = VDDB = VDDR = +5V, load resistance = 500Ω on each output to ground, MGS = 011, LNP = 22dB and fIN = 5MHz, unless otherwise noted. The input to the preamp (LNP) is single-ended, and the output from the VCA is single-ended unless otherwise noted. This results in a 6dB reduction in signal amplitude compared to differential operation. HARMONIC DISTORTION vs FREQUENCY (Differential, 2VPP, MGS = 000) –40 –50 –55 –60 –65 –70 –75 –80 –85 –55 –60 –65 –70 –75 –80 –90 0.1 –30 1 10 –45 1 Frequency (Hz) HARMONIC DISTORTION vs FREQUENCY (Differential, 2VPP, MGS = 111) HARMONIC DISTORTION vs FREQUENCY (Single-Ended, 1VPP, MGS = 000) –40 –50 –55 –60 –65 –70 10 VCACNTL = 0.2V, H2 VCACNTL = 0.2V, H3 VCACNTL = 3.0V, H2 VCACNTL = 3.0V, H3 –45 Harmonic Distortion (dBc) –40 0.1 Frequency (MHz) VCACNTL = 0.2V, H2 VCACNTL = 0.2V, H3 VCACNTL = 3.0V, H2 VCACNTL = 3.0V, H3 –35 Harmonic Distortion (dBc) –50 –85 –90 –50 –55 –60 –65 –70 –75 –80 –85 –75 –90 –80 0.1 –40 1 –55 1 Frequency (MHz) Frequency (MHz) HARMONIC DISTORTION vs FREQUENCY (Single-Ended, 1VPP, MGS = 011) HARMONIC DISTORTION vs FREQUENCY (Single-Ended, 1VPP, MGS = 111) –30 –60 –65 –70 –75 –80 –85 10 VCACNTL = 0.2V, H2 VCACNTL = 0.2V, H3 VCACNTL = 3.0V, H2 VCACNTL = 3.0V, H3 –35 Harmonic Distortion (dBc) –50 0.1 10 VCACNTL = 0.2V, H2 VCACNTL = 0.2V, H3 VCACNTL = 3.0V, H2 VCACNTL = 3.0V, H3 –45 Harmonic Distortion (dBc) VCACNTL = 0.2V, H2 VCACNTL = 0.2V, H3 VCACNTL = 3.0V, H2 VCACNTL = 3.0V, H3 –45 Harmonic Distortion (dBc) Harmonic Distortion (dBc) –40 VCACNTL = 0.2V, H2 VCACNTL = 0.2V, H3 VCACNTL = 3.0V, H2 VCACNTL = 3.0V, H3 –45 HARMONIC DISTORTION vs FREQUENCY (Differential, 2VPP, MGS = 011) –40 –45 –50 –55 –60 –65 –70 –75 –80 –90 –85 0.1 1 10 0.1 Frequency (MHz) VCA2612 SBOS117C 1 10 Frequency (MHz) www.ti.com 7 TYPICAL CHARACTERISTICS (Cont.) At TA = +25°C, VDDA = VDDB = VDDR = +5V, load resistance = 500Ω on each output to ground, MGS = 011, LNP = 22dB and fIN = 5MHz, unless otherwise noted. The input to the preamp (LNP) is single-ended, and the output from the VCA is single-ended unless otherwise noted. This results in a 6dB reduction in signal amplitude compared to differential operation. HARMONIC DISTORTION vs VCACNTL (Differential, 2VPP) –45 –55 –60 –65 –70 –75 –55 –60 –65 –70 –75 –80 –80 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 VCACNTL (V) VCACNTL (V) INTERMODULATION DISTORTION (Differential, 2VPP, f = 10MHz) INTERMODULATION DISTORTION (Single-Ended, 1VPP, f = 10MHz) –5 –5 –15 –15 –25 –25 –35 –35 Power (dBFS) Power (dBFS) MGS = 000, H2 MGS = 011, H2 MGS = 111, H2 MGS = 000, H3 MGS = 011, H3 MGS = 111, H3 –50 Harmonic Distortion (dBc) Harmonic Distortion (dBc) –45 MGS = 000, H2 MGS = 011, H2 MGS = 111, H2 MGS = 000, H3 MGS = 011, H3 MGS = 111, H3 –50 HARMONIC DISTORTION vs VCACNTL (Single-Ended, 1VPP) –45 –55 –65 –45 –55 –65 –75 –75 –85 –85 –95 –95 –105 –105 9.96 9.98 10 10.2 9.96 10.4 0 9.98 10 10.2 10.4 Frequency (MHz) Frequency (MHz) –1dB COMPRESSION vs VCACNTL 0 3rd-ORDER INTERCEPT vs VCACNTL –5 –5 –10 –10 IP3 (dBm) PIN (dBm) –15 –15 –20 –25 –20 –25 –30 –35 –30 –40 –35 –45 –40 8 –50 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 VCACNTL (V) VCACNTL (V) VCA2612 www.ti.com SBOS117C TYPICAL CHARACTERISTICS (Cont.) At TA = +25°C, VDDA = VDDB = VDDR = +5V, load resistance = 500Ω on each output to ground, MGS = 011, LNP = 22dB and fIN = 5MHz, unless otherwise noted. The input to the preamp (LNP) is single-ended, and the output from the VCA is single-ended unless otherwise noted. This results in a 6dB reduction in signal amplitude compared to differential operation. OVERLOAD RECOVERY (Differential, VCACNTL = 3.0V, MGS = 111) PULSE RESPONSE (BURSTS) (Differential, VCACNTL = 3.0V, MGS = 111) Output 500mV/div Output 1V/div Input 1mV/div Input 1mV/div 200ns/div 200ns/div GAIN RESPONSE (Differential, VCACNTL Pulsed, MGS = 111) CROSS TALK vs FREQUENCY (Single-Ended, 1Vp-p, MGS = 011) 0 Output 500mV/div –10 Cross Talk (dB) –20 Input 2V/div VCACNTRL = 1.5V –30 –40 –50 VCACNTRL = 0V –60 –70 VCACNTRL = 3.0V –80 –90 100ns/div 1 10 100 Frequency (MHz) CMRR vs FREQUENCY (LNP only) 0 0 –10 –10 –20 –20 –30 VCACNTL = 0.2V –40 CMRR (dB) CMRR (dB) CMRR vs FREQUENCY (VCA only) VCACNTL = 1.4V –50 –60 –30 –40 –50 –60 –70 –70 –80 VCACNTL = 3.0V –90 0.1 1 –80 10 100 0.1 Frequency (MHz) 10 100 Frequency (MHz) VCA2612 SBOS117C 1 www.ti.com 9 TYPICAL CHARACTERISTICS (Cont.) At TA = +25°C, VDDA = VDDB = VDDR = +5V, load resistance = 500Ω on each output to ground, MGS = 011, LNP = 22dB and fIN = 5MHz, unless otherwise noted. The input to the preamp (LNP) is single-ended, and the output from the VCA is single-ended unless otherwise noted. This results in a 6dB reduction in signal amplitude compared to differential operation. GROUP DELAY vs FREQUENCY ICC vs TEMPERATURE 80 79.5 Group Delay (ns) ICC (mA) 79 78.5 78 77.5 77 76.5 76 –40 –25 –10 5 20 35 50 65 80 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 95 VCACNTL = 3.0V VCACNTL = 0.2V 1 10 Temperature (°C) 100 Frequency (MHz) PSRR vs FREQUENCY –45 –40 –35 PSRR (dB) –30 –25 –20 –15 –10 –5 0 5 10 10 100 1k 10k 100k 1M 10M Frequency (Hz) 10 VCA2612 www.ti.com SBOS117C THEORY OF OPERATION The VCA2612 is a dual-channel system consisting of three primary blocks: a Low Noise Preamplifier (LNP), a Voltage Controlled Attenuator (VCA), and a Programmable Gain Amplifier (PGA). For greater system flexibility, an onboard multiplexer is provided for the VCA inputs, selecting either the LNP outputs or external signal inputs. Figure 1 shows a simplified block diagram of the dual-channel system. op amp. The VCM node shown in the drawing is the VCM output (pin 19). Typical R and C values are shown, yielding a high-pass time constant similar to that of the LNP. If a different common-mode referencing method is used, it is important that the common-mode level be within 10mV of the VCM output for proper operation. 1kΩ External InA Channel A Input LNP VCA PGA To VCAIN 47nF Input Signal Channel A Output 1kΩ VCM (+2.5V) Channel B Input LNP VCA MGS PGA Channel B Output FIGURE 2. Recommended Circuit for Coupling an External Signal into the VCA Inputs. External InB FIGURE 1. Simplified Block Diagram of the VCA2612. LNP—OVERVIEW The LNP input may be connected to provide active-feedback signal termination, achieving lower system noise performance than conventional passive shunt termination. Even lower noise performance is obtained if signal termination is not required. The unterminated LNP input impedance is 600kΩ. The LNP can process fully differential or singleended signals in each channel. Differential signal processing results in significantly reduced 2nd-harmonic distortion and improved rejection of common-mode and power supply noise. The first gain stage of the LNP is AC-coupled into its output buffer with a 44µs time constant (3.6kHz high-pass characteristic). The buffered LNP outputs are designed to drive the succeeding VCA directly or, if desired, external loads as low as 135Ω with minimal impact on signal distortion. The LNP employs very low impedance local feedback to achieve stable gain with the lowest possible noise and distortion. Four pin-programmable gain settings are available: 5dB, 17dB, 22dB, and 25dB. Additional intermediate gains can be programmed by adding trim resistors between the Gain Strap programming pins. VCA—OVERVIEW The magnitude of the differential VCA input signal (from the LNP or an external source) is reduced by a programmable attenuation factor, set by the analog VCA Control Voltage (VCACNTL) at pin 43. The maximum attenuation factor is further programmable by using the three MGS bits (pins 4042). Figure 3 illustrates this dual-adjustable characteristic. Internally, the signal is attenuated by having the analog VCACNTL vary the channel resistance of a set of shuntconnected FET transistors. The MGS bits effectively adjust the overall size of the shunt FET by switching parallel components in or out under logic control. At any given maximum gain setting, the analog variable gain characteristic is linear in dB as a function of the control voltage, and is created as a piecewise approximation of an ideal dB-linear transfer function. The VCA gain control circuitry is common to both channels of the VCA2612. 0 VCA Attenuation (dB) Analog Control VCA Control Maximum Gain Select The common-mode DC level at the LNP output is nominally 2.5V, matching the input common-mode requirement of the VCA for simple direct coupling. When external signals are fed to the VCA, they should also be set up with a 2.5VDC common-mode level. Figure 2 shows a circuit that demonstrates the recommended coupling method using an external Minimum Attenuation –24 Maximum Attenuation –45 0 3.0V Control Voltage FIGURE 3. Swept Attenuator Characteristic. VCA2612 SBOS117C www.ti.com 11 PGA OVERVIEW AND OVERALL DEVICE CHARACTERISTICS The VCA2612 includes a built-in reference, common to both channels, to supply a regulated voltage for critical areas of the circuit. This reduces the susceptibility to power supply variation, ripple, and noise. In addition, separate power supply and ground connections are provided for each channel and for the reference circuitry, further reducing interchannel cross-talk. The differential output of the VCA attenuator is then amplified by the PGA circuit block. This post-amplifier is programmed by the same MGS bits that control the VCA attenuator, yielding an overall swept-gain amplifier characteristic in which the VCA • PGA gain varies from 0dB (unity) to a programmable peak gain of 24dB, 27dB, 30dB, 33dB, 36dB, 39dB, 42dB, or 45dB. Further details regarding the design, operation and use of each circuit block are provided in the following sections. The GAIN vs VCACNTL curve on page 4 shows the composite gain control characteristic of the entire VCA2612. Setting VCACNTL to 3.0V causes the digital MGS gain control to step in 3dB increments. Setting VCACNTL to 0V causes all the MGS-controlled gain curves to converge at one point. The gain at the convergence point is the LNP gain less 6dB, because the measurement setup looks at only one side of the differential PGA output, resulting in 6dB lower signal amplitude. LOW NOISE PREAMPLIFIER (LNP)—DETAIL The LNP is designed to achieve a low noise figure, especially when employing active termination. Figure 4 is a simplified schematic of the LNP, illustrating the differential input and output capability. The input stage employs low resistance local feedback to achieve stable low noise, low distortion performance with very high input impedance. Normally, low noise circuits exhibit high power consumption due to the large bias currents required in both input and output stages. The LNP uses a patented technique that combines the input and output stages such that they share the same bias current. Transistors Q4 and Q5 amplify the signal at the gatesource input of Q4, the +IN side of the LNP. The signal is further amplified by the Q1 and Q2 stage, and then by the final Q3 and RL gain stage, which uses the same bias current as the input devices Q4 and Q5. Devices Q6 through Q10 play the same role for signals on the –IN side. ADDITIONAL FEATURES—OVERVIEW Overload protection stages are placed between the attenuator and the PGA, providing a symmetrically clipped output whenever the input becomes large enough to overload the PGA. A comparator senses the overload signal amplitude and substitutes a fixed DC level to prevent undesirable overload recovery effects. As with the previous stages, the VCA is AC-coupled into the PGA. In this case, the coupling time constant varies from 5µs at the highest gain (45dB) to 59µs at the lowest gain (25dB). The differential gain of the LNP is given in Equation (1): R  Gain = 2 •  L   RS  VDD COMP2A COMP1A RL 93Ω Q2 RL 93Ω LNPOUTN To Bias Circuitry Q9 LNPOUTP Buffer CCOMP (External Capacitor) (1) Buffer Q3 Q8 RS1 105Ω RW RS2 34Ω Q4 LNPINP LNPGS1 RW Q7 LNPINN LNPGS2 RS3 17Ω Q10 LNPGS3 Q1 To Bias Circuitry Q5 Q6 FIGURE 4. Schematic of the Low Noise Preamplifier (LNP). 12 VCA2612 www.ti.com SBOS117C where RL is the load resistor in the drains of Q3 and Q8, and RS is the resistor connected between the sources of the input transistors Q4 and Q7. The connections for various RS combinations are brought out to device pins LNPGS1, LNPGS2, and LNPGS3 (pins 13-15 for channel A, 22-24 for channel B). These Gain Strap pins allow the user to establish one of four fixed LNP gain options as shown in Table I. LNP PIN STRAPPING LNP GAIN (dB) LNPGS1, LNPGS2, LNPGS3 Connected Together LNPGS1 Connected to LNPGS3 LNPGS1 Connected to LNPGS2 All Pins Open 25 22 17 5 It is also possible to create other gain settings by connecting an external resistor between LNPGS1 on one side, and LNPGS2 and/or LNPGS3 on the other. In that case, the internal resistor values shown in Figure 4 should be combined with the external resistor to calculate the effective value of RS for use in Equation (1). The resulting expression for external resistor value is given in Equation (2). 2R S1RL + 2RFIXRL – Gain • R S1RFIX Gain • R S1 – 2RL NOISE (nV/√Hz) (2) where REXT is the externally selected resistor value needed to achieve the desired gain setting, RS1 is the fixed parallel resistor in Figure 4, and RFIX is the effective fixed value of the remaining internal resistors: RS2, RS3, or (RS2 || RS3) depending on the pin connections. Note that the best process and temperature stability will be achieved by using the pre-programmed fixed gain options of Table I, since the gain is then set entirely by internal resistor ratios, which are typically accurate to ±0.5%, and track quite well over process and temperature. When combining external resistors with the internal values to create an effective RS value, note that the internal resistors have a typical temperature coefficient of +700ppm/°C and an absolute value tolerance of approximately ±5%, yielding somewhat less predictable and stable gain settings. With or without external resistors, the board layout should use short Gain Strap connections to minimize parasitic resistance and inductance effects. The overall noise performance of the VCA2612 will vary as a function of gain. Table II shows the typical input- and output-referred noise densities of the entire VCA2612 for maximum VCA and PGA gain; i.e., VCACNTL set to 3.0V and all MGS bits set to 1. Note that the input-referred noise values include the contribution of a 50Ω fixed source impedance, and are therefore somewhat larger than the intrinsic input noise. As the LNP gain is reduced, the noise contribution from the VCA/PGA portion becomes more significant, resulting in higher input-referred noise. However, the outputreferred noise, which is indicative of the overall SNR at that gain setting, is reduced. Input-Referred Output-Referred 25 22 17 5 1.54 1.59 1.82 4.07 2260 1650 1060 597 The LNP is capable of generating a 2VPP differential signal. The maximum signal at the LNP input is therefore 2VPP divided by the LNP gain. An input signal greater than this would exceed the linear range of the LNP, an especially important consideration at low LNP gain settings. ACTIVE FEEDBACK WITH THE LNP One of the key features of the LNP architecture is the ability to employ active-feedback termination to achieve superior noise performance. Active feedback termination achieves a lower noise figure than conventional shunt termination, essentially because no signal current is wasted in the termination resistor itself. Another way to understand this is as follows: Consider first that the input source, at the far end of the signal cable has a cable-matching source resistance of RS. Using conventional shunt termination at the LNP input, a second terminating resistor of value RS is connected to ground. Therefore, the signal loss is 6dB due to the voltage divider action of the series and shunt RS resistors. The effective source resistance has been reduced by the same factor of 2, but the noise contribution has been reduced by only the √2, only a 3dB reduction. Therefore, the net theoretical SNR degradation is 3dB, assuming a noise-free amplifier input. (In practice, the amplifier noise contribution will degrade both the unterminated and the terminated noise figures, somewhat reducing the distinction between them.) See Figure 5 for an amplifier using active feedback. This diagram appears very similar to a traditional inverting amplifier. However, the analysis is somewhat different because the gain A in this case is not a very large open-loop op amp gain; rather, it is the relatively low and controlled gain of the LNP itself. Thus, the impedance at the inverting amplifier terminal will be reduced by a finite amount, as given in the familiar relationship of Equation (3): RIN = RF (1 + A) (3) where RF is the feedback resistor (supplied externally between the LNPINP and FB terminals for each channel), A is the user-selected gain of the LNP, and RIN is the resulting amplifier input impedance with active feedback. In this case, unlike the conventional termination above, both the signal voltage and the RS noise are attenuated by the same factor VCA2612 SBOS117C LNP GAIN (dB) TABLE II. Noise Performance for MGS = 111 and VCACNTL = 3.0V. TABLE I. Pin Strappings of the LNP for Various Gains. REXT = To preserve the low noise performance of the LNP, the user should take care to minimize resistance in the input lead. A parasitic resistance of only 10Ω will contribute 0.4nV/√Hz. www.ti.com 13 VCA NOISE = 3.8nV√Hz, LNP GAIN = 20dB 14 RF LNP Noise nV/√Hz 6.0E-10 8.0E-10 1.0E-09 1.2E-09 1.4E-09 1.6E-09 1.8E-09 2.0E-09 12 RS Noise Figure (dB) LNPIN A RIN RIN = RF 1+A Active Feedback = RS 10 8 6 4 2 RS 0 0 A 100 200 300 400 500 600 700 800 900 1000 RS Source Impedance (Ω) FIGURE 7. Noise Figure for Conventional Termination. Conventional Cable Termination FIGURE 5. Configurations for Active Feedback and Conventional Cable Termination. of two (6dB) before being re-amplified by the A gain setting. This avoids the extra 3dB degradation due to the square-root effect described above, the key advantage of the active termination technique. As mentioned above, the previous explanation ignored the input noise contribution of the LNP itself. Also, the noise contribution of the feedback resistor must be included for a completely correct analysis. The curves given in Figures 6 and 7 allow the VCA2612 user to compare the achievable noise figure for active and conventional termination methods. The left-most set of data points in each graph give the results for typical 50Ω cable termination, showing the worst noise figure but also the greatest advantage of the active feedback method. A switch, controlled by the FBSWCNTL signal on pin 45, enables the user to reduce the feedback resistance by adding an additional parallel component, connected between the LNPINP and SWFB terminals. The two different values of feedback resistance will result in two different values of active-feedback input resistance. Thus, the activefeedback impedance can be optimized at two different LNP gain settings. The switch is connected at the buffered output of the LNP and has an ON resistance of approximately 1Ω. When employing active feedback, the user should be careful to avoid low-frequency instability or overload problems. Figure 8 illustrates the various low-frequency time constants. Referring again to the input resistance calculation of Equation (3), and considering that the gain term A falls off below 3.6kHz, it is evident that the effective LNP input impedance will rise below 3.6kHz, with a DC limit of approximately RF. To avoid interaction with the feedback pole/zero at low frequencies, and to avoid the higher signal levels resulting from the rising impedance characteristic, it is recommended that the external RFCC time constant be set to about 5µs. RF VCA NOISE = 3.8nV√Hz, LNP GAIN = 20dB 9 LNP Noise nV/√Hz 6.0E-10 8.0E-10 1.0E-09 1.2E-09 1.4E-09 1.6E-09 1.8E-09 2.0E-09 8 Noise Figure (dB) 7 6 5 4 3 VCM CF 0.001µF 1MΩ 44pF CC Buffer LNPOUTN RS 2 44pF LNPOUTP 1 0 0 100 200 300 400 500 600 700 800 900 1000 Source Impedance (Ω) (VCA) LNP FIGURE 6. Noise Figure for Active Termination. 14 Buffer Gain Stage 1MΩ VCM FIGURE 8. Low Frequency LNP Time Constants. VCA2612 www.ti.com SBOS117C Achieving the best active feedback architecture is difficult with conventional op amp circuit structures. The overall gain A must be negative in order to close the feedback loop, the input impedance must be high to maintain low current noise and good gain accuracy, but the gain ratio must be set with very low value resistors to maintain good voltage noise. Using a two-amplifier configuration (noninverting for high impedance plus inverting for negative feedback reasons) results in excessive phase lag and stability problems when the loop is closed. The VCA2612 uses a patented architecture that achieves these requirements, with the additional benefits of low power dissipation and differential signal handling at both input and output. For greatest flexibility and lowest noise, the user may wish to shape the frequency response of the LNP. The COMP1 and COMP2 pins for each channel (pins 10 and 11 for channel A, pins 26 and 27 for channel B) correspond to the drains of Q3 and Q8 in Figure 4. A capacitor placed between these pins will create a single-pole low-pass response, in which the effective R of the RC time constant is approximately 186Ω. COMPENSATION WHEN USING ACTIVE FEEDBACK associated with the input connection. Equation 4 relates the bandwidth to the various impedances that are connected to the LNP. BW = (A + 1) RI + RF 2pC(RI )(RF ) (4) LNP OUTPUT BUFFER The differential LNP output is buffered by wideband class AB voltage followers which are designed to drive low impedance loads. This is necessary to maintain LNP gain accuracy, since the VCA input exhibits gain-dependent input impedance. The buffers are also useful when the LNP output is brought out to drive external filters or other signal processing circuitry. Good distortion performance is maintained with buffer loads as low as 135Ω. As mentioned previously, the buffer inputs are AC-coupled to the LNP outputs with a 3.6kHz high-pass characteristic, and the DC common-mode level is maintained at the correct VCM for compatibility with the VCA input. VOLTAGE-CONTROLLED ATTENUATOR (VCA)—DETAIL The typical open-loop gain versus frequency characteristic for the LNP is shown in Figure 9. The –3dB bandwidth is approximately 180MHz and the phase response is such that when feedback is applied the LNP will exhibit a peaked response or might even oscillate. One method for compensating for this undesirable behavior is to place a compensation capacitor at the input to the LNP, as shown in Figure 10. This method is effective when the desired –3dB bandwidth is much less than the open-loop bandwidth of the LNP. This compensation technique also allows the total compensation capacitor to include any stray or cable capacitance that is –3dB Bandwidth Gain 25dB 180MHz FIGURE 9. Open-Loop Gain Characteristic of LNP. The VCA is designed to have a dB-linear attenuation characteristic, i.e. the gain loss in dB is constant for each equal increment of the VCA CNTL control voltage. See Figure 11 for a diagram of the VCA. The attenuator is essentially a variable voltage divider consisting of one series input resistor, RS, and ten identical shunt FETs, placed in parallel and controlled by sequentially activated clipping amplifiers. Each clipping amplifier can be thought of as a specialized voltage comparator with a soft transfer characteristic and well-controlled output limit voltages. The reference voltages V1 through V10 are equally spaced over the 0V to 3.0V control voltage range. As the control voltage rises through the input range of each clipping amplifier, the amplifier output will rise from 0V (FET completely ON) to VCM –VT (FET nearly OFF ), where VCM is the common source voltage and VT is the threshold voltage of the FET. As each FET approaches its OFF state and the control voltage continues to rise, the next clipping amplifier/FET combination takes over for the next portion of the piecewise-linear attenuation characteristic. Thus, low control voltages have most of the FETs turned ON, while high control voltages have most turned OFF. Each FET acts to decrease the shunt resistance of the voltage divider formed by RS and the parallel FET network. The attenuator is comprised of two sections, with five parallel clipping amplifier/FET combinations in each. Special reference circuitry is provided so that the (VCM –VT) limit voltage will track temperature and IC process variations, minimizing the effects on the attenuator control characteristic. RF RI Input C A Output In addition to the analog VCACNTL gain setting input, the attenuator architecture provides digitally programmable adjustment in eight steps, via the three Maximum Gain Setting (MGS) bits. These adjust the maximum achievable gain FIGURE 10. LNP with Compensation Capacitor. VCA2612 SBOS117C www.ti.com 15 Attenuator Input RS A1 - A10 Attenuator Stages Attenuator Output QS Q1 VCM A1 Q2 A2 C1 A3 C2 V1 Q3 A4 C3 V2 Q4 A5 C4 V3 V4 Control Input Q5 Q6 A6 C5 A7 C6 V5 Q7 V6 Q8 A8 C7 V7 Q9 A9 C8 Q10 A10 C9 V8 C10 V9 V10 C1 - C10 Clipping Amplifiers 0dB –4.5dB Attenuation Characteristic of Individual FETs VCM-VT 0 V1 V2 V3 V4 V5 V6 V7 V8 V9 Characteristic of Attenuator Control Stage Output V10 OVERALL CONTROL CHARACTERISTICS OF ATTENUATOR 0dB –4.5dB 0.3V Control Signal 3V FIGURE 11. Piecewise Approximation to Logarithmic Control Characteristics. (corresponding to minimum attenuation in the VCA, with VCACNTL = 3.0V) in 3dB increments. This function is accomplished by providing multiple FET sub-elements for each of the Q 1 to Q 10 FET shunt elements shown in Figure 11. In the simplified diagram of Figure 12, each shunt FET is shown as two sub-elements, QNA and QNB. Selector 16 switches, driven by the MGS bits, activate either or both of the sub-element FETs to adjust the maximum RON and thus achieve the stepped attenuation options. The VCA can be used to process either differential or singleended signals. Fully differential operation will reduce 2ndharmonic distortion by about 10dB for full-scale signals. VCA2612 www.ti.com SBOS117C RS OUTPUT INPUT Q1A Q1B Q2A Q2B Q3A Q3B Q4A Q4B Q5A Q5B VCM A1 A2 A3 A4 A5 B1 B2 PROGRAMMABLE ATTENUATOR SECTION FIGURE 12. Programmable Attenuator Section. From VCA Input impedance of the VCA will vary with gain setting, due to the changing resistances of the programmable voltage divider structure. At large attenuation factors (i.e., low gain settings), the impedance will approach the series resistor value of approximately 135Ω. Output PGA Comparators Gain = A Selection Logic As with the LNP stage, the VCA output is AC-coupled into the PGA. This means that the attenuation-dependent DC common-mode voltage will not propagate into the PGA, and so the PGA’s DC output level will remain constant. Finally, note that the VCACNTL input consists of FET gate inputs. This provides very high impedance and ensures that multiple VCA2612 devices may be connected in parallel with no significant loading effects. The nominal voltage range for the VCACNTL input spans from 0V to 3V. Over driving this input (≤ 5V) does not affect the performance. E = Maximum Peak Amplitude – E E A A FIGURE 13. Overload Protection Circuitry. VCACNTL = 0.2V, DIFFERENTIAL, MGS = 100, (0dB) OVERLOAD RECOVERY CIRCUITRY—DETAIL 1V/div Output Input 200ns/div FIGURE 14. Overload Recovery Response For Minimum Gain. VCACNTL = 3.0V, DIFFERENTIAL, MGS = 100, (36dB) Output 1V/div With a maximum overall gain of 70dB, the VCA2612 is prone to signal overloading. Such a condition may occur in either the LNP or the PGA depending on the various gain and attenuation settings available. The LNP is designed to produce low-distortion outputs as large as 1VPP single-ended (2VPP differential). Therefore the maximum input signal for linear operation is 2VPP divided by the LNP differential gain setting. Clamping circuits in the LNP ensure that larger input amplitudes will exhibit symmetrical clipping and short recovery times. The VCA itself, being basically a voltage divider, is intrinsically free of overload conditions. However, the PGA post-amplifier is vulnerable to sudden overload, particularly at high gain settings. Rapid overload recovery is essential in many signal processing applications such as ultrasound imaging. A special comparator circuit is provided at the PGA input which detects overrange signals (detection level dependent on PGA gain setting). When the signal exceeds the comparator input threshold, the VCA output is blocked and an appropriate fixed DC level is substituted, providing fast and clean overload recovery. The basic architecture is shown in Figure 13. Both high and low overrange conditions are sensed and corrected by this circuit. Input Figures 14 and 15 show typical overload recovery waveforms with MGS = 100, for VCA + PGA minimum gain (0dB) and maximum gain (36dB), respectively. LNP gain is set to 25dB in both cases. 200ns/div FIGURE 15. Overload Recovery Response For Maximum Gain. VCA2612 SBOS117C www.ti.com 17 INPUT OVERLOAD RECOVERY that setting. Therefore, the VCA + PGA overall gain will always be 0dB (unity) when the analog VCACNTL input is set to 0V (= maximum attenuation). For VCACNTL = 3V (no attenuation), the VCA + PGA gain will be controlled by the programmed PGA gain (24dB to 45dB in 3dB steps). One of the most important applications for the VCA2612 is processing signals in an ultrasound system. The ultrasound signal flow begins when a large signal is applied to a transducer, which converts electrical energy to acoustic energy. It is not uncommon for the amplitude of the electrical signal that is applied to the transducer to be ±50V or greater. To prevent damage, it is necessary to place a protection circuit between the transducer and the VCA2612, as shown in Figure 16. Care must be taken to prevent any signal from turning the ESD diodes on. Turning on the ESD diodes inside the VCA2612 could cause the input coupling capacitor (CC) to charge to the wrong value. For clarity, the gain and attenuation factors are detailed in Table III. MGS ATTENUATOR GAIN DIFFERENTIAL SETTING VCACNTL = 0V to 3V PGA GAIN 000 001 010 011 100 101 110 111 VDD CF RF –24dB to 0dB –27dB to 0dB –30dB to 0dB –33dB to 0dB –36dB to 0dB –39dB to 0dB –42dB to 0dB –45dB to 0dB 24dB 27dB 30dB 33dB 36dB 39dB 42dB 45dB ATTENUATOR + DIFF. PGA GAIN 0dB to 24dB 0dB to 27dB 0dB to 30dB 0dB to 33dB 0dB to 36dB 0dB to 39dB 0dB to 42dB 0dB to 45dB TABLE III. MGS Settings. LNPINP Protection Network LNP The PGA architecture consists of a differential, programmable-gain voltage to current converter stage followed by transimpedance amplifiers to create and buffer each side of the differential output. The circuitry associated with the voltage to current converter is similar to that previously described for the LNP, with the addition of eight selectable PGA gain-setting resistor combinations (controlled by the MGS bits) in place of the fixed resistor network used in the LNP. Low input noise is also a requirement of the PGA design due to the large amount of signal attenuation which can be inserted between the LNP and the PGA. At minimum VCA attenuation (used for small input signals) the LNP noise dominates; at maximum VCA attenuation (large input signals) the PGA noise dominates. Note that if the PGA output is used single-ended, the apparent gain will be 6dB lower. LNPOUTN ESD Diode FIGURE 16. VCA2612 Diode Bridge Protection Circuit. PGA POST-AMPLIFIER—DETAIL Figure 17 shows a simplified circuit diagram of the PGA block. As described previously, the PGA gain is programmed with the same MGS bits which control the VCA maximum attenuation factor. Specifically, the PGA gain at each MGS setting is the inverse (reciprocal) of the maximum VCA attenuation at VDD To Bias Circuitry Q1 RL Q11 VCAOUTP Q12 Q9 Q3 RL VCAOUTN Q8 VCM RS1 VCM Q13 RS2 Q4 +In Q7 –In Q14 Q2 Q10 Q5 Q6 To Bias Circuitry FIGURE 17. Simplified Block Diagram of the PGA Section Within the VCA2612. 18 VCA2612 www.ti.com SBOS117C PACKAGE OPTION ADDENDUM www.ti.com 20-Apr-2011 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Drawing Pins Package Qty Eco Plan (2) Lead/ Ball Finish MSL Peak Temp (3) Samples (Requires Login) VCA2612Y/250 ACTIVE TQFP PFB 48 250 TBD Call TI Call TI VCA2612Y/250G4 ACTIVE TQFP PFB 48 250 TBD Call TI Call TI VCA2612Y/2K ACTIVE TQFP PFB 48 2000 TBD Call TI Call TI VCA2612Y/2KG4 ACTIVE TQFP PFB 48 2000 TBD Call TI Call TI (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. TBD: The Pb-Free/Green conversion plan has not been defined. Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes. Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above. Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material) (3) MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals. TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release. In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis. Addendum-Page 1 MECHANICAL DATA MTQF019A – JANUARY 1995 – REVISED JANUARY 1998 PFB (S-PQFP-G48) PLASTIC QUAD FLATPACK 0,27 0,17 0,50 36 0,08 M 25 37 24 48 13 0,13 NOM 1 12 5,50 TYP 7,20 SQ 6,80 9,20 SQ 8,80 Gage Plane 0,25 0,05 MIN 0°– 7° 1,05 0,95 Seating Plane 0,75 0,45 0,08 1,20 MAX 4073176 / B 10/96 NOTES: A. All linear dimensions are in millimeters. B. This drawing is subject to change without notice. C. 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