VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 8-Channel, Ultralow-Power, Variable Gain Amplifier with Low-Noise Pre-Amp FEATURES APPLICATIONS • Ultralow Power: 65mW/Channel • Low Noise: 0.
VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 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.
VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 ELECTRICAL CHARACTERISTICS All specifications at TA = +25°C, AVDD2 = 5.0V, AVDD1 = DVDD = 3.3V; single-ended, ac-coupled (1µF) input configuration to the preamp (LNA), fIN = 5MHz, VCNTL = 1.0V, PG = 30dB, clamp disabled (CL = 1), LPF = 15MHz, and RLOAD = 1kΩ on each output to ground, unless otherwise noted.
VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 ELECTRICAL CHARACTERISTICS (continued) All specifications at TA = +25°C, AVDD2 = 5.0V, AVDD1 = DVDD = 3.3V; single-ended, ac-coupled (1µF) input configuration to the preamp (LNA), fIN = 5MHz, VCNTL = 1.0V, PG = 30dB, clamp disabled (CL = 1), LPF = 15MHz, and RLOAD = 1kΩ on each output to ground, unless otherwise noted.
VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 ELECTRICAL CHARACTERISTICS (continued) All specifications at TA = +25°C, AVDD2 = 5.0V, AVDD1 = DVDD = 3.3V; single-ended, ac-coupled (1µF) input configuration to the preamp (LNA), fIN = 5MHz, VCNTL = 1.0V, PG = 30dB, clamp disabled (CL = 1), LPF = 15MHz, and RLOAD = 1kΩ on each output to ground, unless otherwise noted.
VCA8500 www.ti.
VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 Table 1. TERMINAL FUNCTIONS (continued) TERMINAL PIN NO.
VCA8500 www.ti.
VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 INPUT REGISTER BIT MAPS Register Map BYTE #1 BYTE #2 BYTE #3 BYTE #4 BYTE #5 D0:D7 D8:D11 D12:D15 D16:D19 D20:D23 D24:D27 D28:D31 D32:D35 D36:D39 Control CH1 CH2 CH3 CH4 CH5 CH6 CH7 CH8 Table 2. Default Register Configuration D7 D6 D5 D4 D3 D2 D1 D0 0 0 1 0 0 0 1 1 Table 3.
VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 Table 6. Byte 4—Third Data Byte BIT # NAME DESCRIPTION D24 (LSB) DB5:1 Channel 5, LSB of matrix control D25 DB5:2 Channel 5, matrix control D26 DB5:3 Channel 5, matrix control D27 DB5:4 Channel 5, MSB of matrix control D28 DB6:1 Channel 6; LSB of matrix control D29 DB6:2 Channel 6, matrix control D30 DB6:3 Channel 6, matrix control D31 (MSB) DB6:4 Channel 6, MSB of matrix control Table 7.
VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 Table 10.
VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 SERIAL DIGITAL INTERFACE (SDI) • • • • • • All writes and reads are five bytes at a time. Each byte consists of 8 bits, for a total instruction set of 40 bits. Data are latched on the falling edge of CLK. Separate write (DIN) and read data (DOUT) lines. Reads follow the same bitstream pattern seen in the write cycle. Reads extract data from the FIFO buffer, not the latched register.
VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 TYPICAL CHARACTERISTICS All specifications at TA = +25°C, AVDD2 = 5.0V, AVDD1 = DVDD = 3.3V; single-ended, ac-coupled (1µF) input configuration to the preamp (LNA), fIN = 5MHz, VCNTL = 1.0V, clamp disabled (CL = 1), LPF = 15MHz, and RLOAD = 1kΩ on each output to ground, unless otherwise noted. GAIN ERROR vs VCNTRL 0.50 27dB 0.
VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 TYPICAL CHARACTERISTICS (continued) All specifications at TA = +25°C, AVDD2 = 5.0V, AVDD1 = DVDD = 3.3V; single-ended, ac-coupled (1µF) input configuration to the preamp (LNA), fIN = 5MHz, VCNTL = 1.0V, clamp disabled (CL = 1), LPF = 15MHz, and RLOAD = 1kΩ on each output to ground, unless otherwise noted. GAIN MATCH AT VCNTRL = 0.1V GAIN MATCH AT VCNTRL = 0.
VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 TYPICAL CHARACTERISTICS (continued) All specifications at TA = +25°C, AVDD2 = 5.0V, AVDD1 = DVDD = 3.3V; single-ended, ac-coupled (1µF) input configuration to the preamp (LNA), fIN = 5MHz, VCNTL = 1.0V, clamp disabled (CL = 1), LPF = 15MHz, and RLOAD = 1kΩ on each output to ground, unless otherwise noted. CW CURRENT vs TEMPERATURE +3.
VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 TYPICAL CHARACTERISTICS (continued) All specifications at TA = +25°C, AVDD2 = 5.0V, AVDD1 = DVDD = 3.3V; single-ended, ac-coupled (1µF) input configuration to the preamp (LNA), fIN = 5MHz, VCNTL = 1.0V, clamp disabled (CL = 1), LPF = 15MHz, and RLOAD = 1kΩ on each output to ground, unless otherwise noted.
VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 TYPICAL CHARACTERISTICS (continued) All specifications at TA = +25°C, AVDD2 = 5.0V, AVDD1 = DVDD = 3.3V; single-ended, ac-coupled (1µF) input configuration to the preamp (LNA), fIN = 5MHz, VCNTL = 1.0V, clamp disabled (CL = 1), LPF = 15MHz, and RLOAD = 1kΩ on each output to ground, unless otherwise noted. NOISE FIGURE vs FREQUENCY OVER RS INPUT-REFERRED NOISE 3.5 1.00 3.0 0.95 2MHz 2.5 Noise (nV/ÖHz) 2.0 RS = 1kW 1.5 1.
VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 TYPICAL CHARACTERISTICS (continued) All specifications at TA = +25°C, AVDD2 = 5.0V, AVDD1 = DVDD = 3.3V; single-ended, ac-coupled (1µF) input configuration to the preamp (LNA), fIN = 5MHz, VCNTL = 1.0V, clamp disabled (CL = 1), LPF = 15MHz, and RLOAD = 1kΩ on each output to ground, unless otherwise noted.
VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 TYPICAL CHARACTERISTICS (continued) All specifications at TA = +25°C, AVDD2 = 5.0V, AVDD1 = DVDD = 3.3V; single-ended, ac-coupled (1µF) input configuration to the preamp (LNA), fIN = 5MHz, VCNTL = 1.0V, clamp disabled (CL = 1), LPF = 15MHz, and RLOAD = 1kΩ on each output to ground, unless otherwise noted.
VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 TYPICAL CHARACTERISTICS (continued) All specifications at TA = +25°C, AVDD2 = 5.0V, AVDD1 = DVDD = 3.3V; single-ended, ac-coupled (1µF) input configuration to the preamp (LNA), fIN = 5MHz, VCNTL = 1.0V, clamp disabled (CL = 1), LPF = 15MHz, and RLOAD = 1kΩ on each output to ground, unless otherwise noted.
VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 TYPICAL CHARACTERISTICS (continued) All specifications at TA = +25°C, AVDD2 = 5.0V, AVDD1 = DVDD = 3.3V; single-ended, ac-coupled (1µF) input configuration to the preamp (LNA), fIN = 5MHz, VCNTL = 1.0V, clamp disabled (CL = 1), LPF = 15MHz, and RLOAD = 1kΩ on each output to ground, unless otherwise noted.
VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 TYPICAL CHARACTERISTICS (continued) All specifications at TA = +25°C, AVDD2 = 5.0V, AVDD1 = DVDD = 3.3V; single-ended, ac-coupled (1µF) input configuration to the preamp (LNA), fIN = 5MHz, VCNTL = 1.0V, clamp disabled (CL = 1), LPF = 15MHz, and RLOAD = 1kΩ on each output to ground, unless otherwise noted. PGA OVERLOAD (VIN = 50mVPP, Clamp Enabled) Input CH 1 (50mV/div) PGA = 20dB VOUT = 1.7VPP VCNTRL = 1V Output CH 2 (0.
VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 THEORY OF OPERATION Built on TI’s bipolar-complementary (BiCOM) process, the VCA8500 is a third-generation, octal variable gain amplifier that implements a number of proprietary circuit design techniques to specifically address the performance demands of medical ultrasound systems. The VCA8500 is an 8-channel VGA that is ideally suited for portable ultrasound applications.
VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 LOW-NOISE AMPLIFIER (LNA) As with many high-gain systems, the front-end amplifier is critical to achieve a certain overall performance level. Using a proprietary new architecture, the LNA of the VCA8500 delivers exceptional low-noise performance, while operating on a very low quiescent current of only 8.3mA per channel. This current consumption is significantly lower compared to CMOS-based architectures with similar noise performances.
VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 PROGRAMMABLE POST-GAIN AMPLIFIER (PGA) Following the VCA is a programmable post-gain amplifier (PGA). Figure 62 shows a simplified schematic of the PGA, including the clamping stage. The gain of this PGA can be configured to four different gain settings: 20dB, 25dB, 27dB, and 30dB, programmable through the serial port; see Table 8.
VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 APPLICATION INFORMATION This architecture minimizes any loading of the signal source that may otherwise lead to a frequency-dependent voltage divider. Moreover, the closed-loop design yields very low offsets and offset drift; this consideration is important because the LNA directly drives the subsequent voltage-controlled attenuator.
VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 OVERLOAD RECOVERY are largely determined by the biasing current of the diodes, which can be set by adjusting the 3kΩ resistor values; for example, setting a higher current level may lead to an improved switching characteristic and reduced noise contribution. A typical front-end protection circuitry may add in the order of 2nV/√Hz of noise to the signal path. This slight increase also depends on the value of the termination resistor (RT).
VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 VCA—GAIN CONTROL The attenuator (VCA) for each of the eight channels of the VCA8500 is controlled by a single-ended control signal input, the VCNTRL pin. The control voltage range spans from 0V to 1.2V, referenced to ground. This control voltage varies the attenuation of the VCA based on its linear-in-dB characteristic with its maximum attenuation (minimum gain) at VCNTRL = 0V, and minimum attenuation (maximum gain) at VCNTRL = 1.2V.
VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 INTERFACING TO ADCs The VCA8500 is ideally suited to drive the ADS5281, a low-power, octal, 12-bit ADC that can be operated at sampling rates of up to 50MSPS. The VCA outputs can be directly connected the ADC inputs without the need for any external components, as shown in Figure 67.
VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 The resulting signal current then passes through the 8×10 switch matrix. Depending on the programmed configuration of the switch matrix, any V/I amplifier current output can be connected to any of 10 CW outputs. This design is a simple current-summing circuit such that each CW output can represent the sum of any or all of the channel currents.
VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 POWER SUPPLIES The VCA8500 operates on two supply rails, a +3.3V and a +5V supply. At initial power-up, the part operates in the TGC mode, with the registers in the default configurations (see Table 2). In TGC mode, only the VCA (attenuator) draws a small current (typically 1.5mA) from the +5V supply.
VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 +5V C16 1m F OUT8P C25 0.1mF C14 0.1mF C15 1m F C35 0.1mF IN7 C24 0.1mF C3 0.
VCA8500 www.ti.com SBOS390A – JANUARY 2008 – REVISED MARCH 2008 GROUNDING AND BYPASSING The VCA8500 uses a thermally-enhanced QFN package, with an exposed PowerPAD on the back side of the package. This backside pad is the only ground reference point of the VCA8500, and it should be connected to a low-noise system ground plane. All bypassing and power supplies for the VCA8500 should be referenced to this ground point. All supply pins should be bypassed with 0.
PACKAGE OPTION ADDENDUM www.ti.
PACKAGE MATERIALS INFORMATION www.ti.com 16-Feb-2012 TAPE AND REEL INFORMATION *All dimensions are nominal Device Package Package Pins Type Drawing SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) B0 (mm) K0 (mm) P1 (mm) W Pin1 (mm) Quadrant VCA8500IRGCR VQFN RGC 64 2000 330.0 16.4 9.3 9.3 1.5 12.0 16.0 Q2 VCA8500IRGCT VQFN RGC 64 250 330.0 16.4 9.3 9.3 1.5 12.0 16.
PACKAGE MATERIALS INFORMATION www.ti.com 16-Feb-2012 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) VCA8500IRGCR VQFN RGC 64 2000 336.6 336.6 28.6 VCA8500IRGCT VQFN RGC 64 250 336.6 336.6 28.
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