In this configuration, the input offset voltage of the main amplifier is nulled. Also, external capacitor CXB stores the nulling potential to allow the offset voltage of the main amplifier to remain nulled during the next nulling phase. This continuous chopping process allows offset voltage nulling during variations in time and temperature over the common-mode input voltage range and power supply range. In addition, because the low-frequency signal path is through both the null and main amplifiers, extremely high gain is achieved. The low-frequency noise of a chopper amplifier depends on the magnitude of the component noise prior to chopping and the capability of the circuit to reduce this noise while chopping. The use of the Advanced LinCMOS process, with its low-noise analog MOS transistors and patent-pending input stage design, significantly reduces the input noise voltage.
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This process in conjunction with unique chopper-stabilization circuitry produces opera tional amplifiers whose performance matches or exceeds that of similar devices available today. Chopper-stabilization techniques make possible extremely high dc precision by continuously nulling input offset voltage even during variation in temperature, time, common-mode voltage, and power supply voltage. In addition, low-frequency noise voltage is significantly reduced. This high precision, coupled with the extremely high input impedance of the CMOS input stage, makes the TLC and TLCA an ideal choice for low-level signal processing applications such as strain gauges, thermocouples, and other transducer amplifiers.
For applications that require extremely low noise and higher usable bandwidth, use the TLC or TLCA device, which has a chopping frequency of 10 kHz.
On all other products, production processing does not necessarily include testing of all parameters. Two external capacitors are required for operation of the device; however, the on-chip chopper-control circuitry is transparent to the user.
On devices in the pin and pin packages, the control circuitry is made accessible to allow the user the option of controlling the clock frequency with an external frequency source. 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.
Products conform to specifications per the terms of Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. If desired, an output clamp pin is available to reduce the recovery time even further. The device inputs and output are designed to withstand — mA surge currents without sustaining latch-up. Add R suffix to the device type e. Thermal compression or ultrasonic bonding may be used on the doped-aluminum bonding pads.
Chips may be mounted with conductive epoxy or a gold-silicon preform. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated under "recommended operating conditions" is not implied.
Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability. NOTES: 1. The output may be shorted to either supply.
NOTES: 4. Output clamp is not connected. For other test requirements, please contact the factory. This statement has no bearing on testing or nontesting of other parameters. This parameter is not production tested. Thermocouple effects preclude measurement of the actual VIO of these devices in high speed automated testing.
VIO is measured to a limit determined by the test equipment capability at the temperature extremes. The test ensures that the stabilization circuitry is performing properly. Both factors can cause system degradation, negating the performance advantages realized by using the TLC Degradation from capacitor leakage becomes more apparent with the increasing temperatures.
In addition, guard bands are recommended around the capacitor connections on both sides of the printed circuit board to alleviate problems caused by surface leakage on circuit boards. Capacitors with high dielectric absorption tend to take several seconds to settle upon application of power, which directly affects input offset voltage.
In applications where fast settling of input offset voltage is needed, it is recommended that high-quality film capacitors, such as mylar, polystyrene, or polypropylene, be used. In other applications, however, a ceramic or other low-grade capacitor can suffice. On many choppers, connecting these capacitors to VDD — causes degradation in noise performance.
This problem is eliminated on the TLC To use the internal Hz clock, no connection is necessary. The external clock trip point is 2. Once the overdrive condition is removed, a period of time is required to allow the built-up charge to dissipate. This time period is defined as overload recovery time see Figure Typical overload recovery time for the TLC is significantly faster than competitive products; however, if required, this time can be reduced further by use of internal clamp circuitry accessible through CLAMP if required.
Overload Recovery The clamp is a switch that is automatically activated when the output is approximately 1 V from either supply rail. When connected to the inverting input in parallel with the closed-loop feedback resistor , the closed-loop gain is reduced, and the TLC output is prevented from going into saturation. Since the output must source sink current through the switch see Figure 7 , the maximum output voltage swing is slightly reduced.
Dissimilar metal junctions can produce thermoelectric voltages in the range of several microvolts per degree Celsius orders of magnitude greater than the 0. To help minimize thermoelectric effects, careful attention should be paid to component selection and circuit-board layout. Avoid the use of nonsoldered connections such as sockets, relays, switches, etc.
Cancel thermoelectric effects by duplicating the number of components and junctions in each device input. The use of low-thermoelectric-coefficient components, such as wire-wound resistors, is also beneficial. Internal protection diodes should not, by design, be forward biased. Applied input and output voltages should not exceed the supply voltage by more than mV.
Care should be exercised when using capacitive coupling on pulse generators. Supply transients should be shunted by the use of decoupling capacitors 0. The current path established if latch-up occurs is usually between the supply rails and is limited only by the impedance of the power supply and the forward resistance of the parasitic thyristor. The chance of latch-up occurring increases with increasing temperature and supply voltage.
Care should be exercised in handling these devices, as exposure to ESD may result in degradation of the device parametric performance. This superior performance is the result of using two operational amplifiers, a main amplifier and a nulling amplifier, plus oscillator-controlled logic and two external capacitors to create a system that behaves as a single amplifier.
The TLC on-chip control logic produces two dominant clock phases: a nulling phase and an amplifying phase. The term chopper-stabilized derives from the process of switching between these two clock phases. Figure 34 shows a simplified block diagram of the TLC Switches A and B are make-before-break types. During the nulling phase, switch A is closed shorting the nulling amplifier inputs together and allowing the nulling amplifier to reduce its own input offset voltage by feeding its output signal back to an inverting input node.
Simultaneously, external capacitor CXA stores the nulling potential to allow the offset voltage of the amplifier to remain nulled during the amplifying phase. In this configuration, the input offset voltage of the main amplifier is nulled. Also, external capacitor CXB stores the nulling potential to allow the offset voltage of the main amplifier to remain nulled during the next nulling phase.
This continuous chopping process allows offset voltage nulling during variations in time and temperature over the common-mode input voltage range and power supply range. In addition, because the low-frequency signal path is through both the null and main amplifiers, extremely high gain is achieved. The low-frequency noise of a chopper amplifier depends on the magnitude of the component noise prior to chopping and the capability of the circuit to reduce this noise while chopping.
The use of the Advanced LinCMOS process, with its low-noise analog MOS transistors and patent-pending input stage design, significantly reduces the input noise voltage. The primary source of nonideal operation in chopper-stabilized amplifiers is error charge from the switches. As charge imbalance accumulates on critical nodes, input offset voltage can increase, especially with increasing chopping frequency.
The TLC incorporates a feed-forward design that ensures continuous frequency response. Essentially, the gain magnitude of the nulling amplifier and compensation network crosses unity at the break frequency of the main amplifier. As a result, the high-frequency response of the system is the same as the frequency response of the main amplifier.
This approach also ensures that the slewing characteristics remain the same during both the nulling and amplifying phases. All linear dimensions are in inches millimeters. This drawing is subject to change without notice. Body dimensions do not include mold flash or protrusion, not to exceed 0. This package can be hermetically sealed with a metal lid.
The terminals are gold plated. This package can be hermetically sealed with a ceramic lid using glass frit. Index point is provided on cap for terminal identification only on press ceramic glass frit seal only.
All products are sold subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability. Testing and other quality control techniques are utilized to the extent TI deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed, except those mandated by government requirements. TI assumes no liability for applications assistance or customer product design.
TI does not warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, or other intellectual property right of TI covering or relating to any combination, machine, or process in which such semiconductor products or services might be or are used. Copyright , Texas Instruments Incorporated.