THS4140 EVM User's Guide for HighĆSpeed FullyĆDifferential Amplifier User’s Guide February 2001 Mixed-Signal Products SLOU106
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Preface About This Manual This manual is written to provide information about the evaluation module of the fully differential amplifier under test. Additionally, this document provides a good example of PCB design for high speed applications. The user should keep in mind the following points. The design of the high-speed amplifier PCB is an elegant and sensitive process. Therefore, the user must approach the PCB design with care and awareness.
Related Documentation From Texas Instruments Information About Cautions and Warnings This book may contain cautions and warnings. This is an example of a caution statement. A caution statement describes a situation that could potentially damage your software or equipment. This is an example of a warning statement. A warning statement describes a situation that could potentially cause harm to you. The information in a caution or a warning is provided for your protection.
Running Title—Attribute Reference Contents 1 Introduction and Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Evaluation Module Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 THS4140 EVM Specifications . . . . . . . . . . . . .
Running Title—Attribute Reference Figures 1–1 1–2 1–3 1–4 1–5 1–6 1–7 1–8 1–9 1–10 1–11 2–1 2–2 2–3 2–4 2–5 Schematic of the Populated Circuit on the EVM (Default Configuration) . . . . . . . . . . . . . . Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fully-Differential In/Fully-Differential Out, Without Transformer . . . . . . . . . . . . . . . . . . . . . .
Chapter 1 Introduction and Description The Texas Instruments THS4140 evaluation module (EVM) helps designers evaluate the performance of the THS4140 operational amplifier. Also, this EVM is a good example of high-speed PCB design. This document details the Texas Instruments THS4140 high-speed operational amplifier evaluation module (EVM).
Description 1.1 Description The THS4140 EVM is a good example of PCB design and layout for high-speed operational amplifier applications. It is a complete circuit for the high-speed operational amplifier. The EVM is made of the THS4140 high-speed operational amplifier, a number of passive components, and various features and footprints that enable the user to experiment, test, and verify various operational amplifier circuit implementations. The board measures 4.5 inches in length by 2.5 inches in width.
THS4140 EVM Specifications 1.3 THS4140 EVM Specifications Supply voltage range, ± VCC . . . . 5 V to ± 15 V (see the device data sheet) Supply current, ICC . . . . . . . . . . . . . . . . . . . . . . . . (see the device data sheet) Output drive, IO, VCC = ± 15 . . . . . . . . . . . . . . . . . (see the device data sheet) For complete THS4140 amplifier IC specifications, parameter measurement information, and additional application information, see the THS4140 data sheet, TI literature number SLOS320. 1.
THS4140 EVM Schematic 1.5 THS4140 EVM Schematic Figure 1–2.
Additional Sample Schematics 1.6 Additional Sample Schematics For verification of jumper locations and other bypass components, see the complete EVM schematic in Figure 1–2. Figure 1–3. Fully-Differential In/Fully-Differential Out, Without Transformer R6b R3B 50 Ω Source RX1 0Ω C4 VCC R1b 0Ω + VIN AC – THS4140 + – R16 Termination Resistor RX2 0Ω R1a 0Ω VCC– C1 R4b Rx4 R10 0Ω R4a 0Ω Rx5 Rx6 0Ω 0Ω C6 VOCM R6a R3a Note: Fully-differential in / fully-differential out signal path.
Additional Sample Schematics Figure 1–5. VICR Level Shifter R6B RPU1 RX3 49.9 Ω 50 Ω Source RX1 0Ω VIN AC 402 Ω VCC C4 VCC R1b R3b 0Ω Rx0 374 Ω R3a 24.9 Ω 374 Ω + – THS4140 + – C1 RPU2 VOCM R4b Rx4 R10 0Ω R4a 0Ω Rx5 49.9 Ω Rx6 0Ω 0Ω 49.9 Ω C6 VCC– R6a 402 Ω Note: Shifting the VICR within the specified range in the data sheet via RPU1 and RPU2 if the VICR is out of the specified range. See the Application section of the data sheet for the THS4140 for more information. Figure 1–6.
THS4140 EVM Layout 1.7 THS4140 EVM Layout Figure 1–7. Top Layer (Silkscreen) TEXAS INSTRUMENTS THS4140 EVM REV_B Figure 1–8.
THS4140 EVM Layout Figure 1–9. Internal Plane (Layer 2) (Ground Plane) Figure 1–10.
THS4140 EVM Layout Figure 1–11.
1-10 Introduction and Description
Chapter 2 Using the THS4140 EVM It is recommended that the user perform the following exercises to learn the usage of the EVM. This practice helps the user learn about the various terminals on the EVM and their function. In addition, it suggests the components and equipment needed to operate the EVM. Topic Page 2.1 Required Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2–2 2.2 Power Supply Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1 Required Equipment - - One double-output dc power supply (±5 V, 100 mA output minimum) Two dc current meters with resolution to 1 mA and capable of the maximum current the dc power supply can supply. If available, set the current limit on the dc power supply to 100 mA. Note: Some power supplies incorporate current meters which may be applicable to this test. 50-Ω source impedance function generator (1 MHz, 10 VPP sine wave) Oscilloscope (50-MHz bandwidth minimum, 50-Ω input impedance). 2.
2.3 Input and Output Setup 1) Ensure that JU3, JU4, and JU1 are not installed (open circuit). 2) Set the function generator to generate a 1 MHz, ±0.5 V (1 VPP) sine wave with no dc offset. 3) Turn off the function generator before proceeding to the next step. 4) Using a BNC-to-SMA cable, connect the function generator to J1 (VI+) on the EVM. 5) Using a BNC-to-SMA cable, connect the oscilloscope to J3 (VO–) on the EVM. 6) Using a BNC-to-SMA cable, connect the oscilloscope to J4 (VO+) on the EVM.
2.4 Testing the EVM Setup 1) Turn on the dc power supply. 2) Verify that both the +5 V (current meter 1) and the –5 V (current meter 2) currents are below 20 mA. Caution: Currents above 20 mA indicate a possible short or a wrong resistor value on the PCB. Do not proceed until this situation is corrected. 3) Turn on the function generator. 4) Verify the oscilloscope is showing two 1 MHz sine waves with amplitude of ±0.125 V. The dc offset of the signal must be below 50 mV.
2.5 Power Down Verification This EVM is used to evaluate devices with and without the shutdown function. Therefore, this step is only applicable if the device has a shutdown function. Please see the data sheet for power-down verification. 1) Insert the jumper JU1 to power down the device. The current consumption (dc current meters) should drop to less than 1.5 mA.
Butterworth Filter Note: Transformers are used to change the single ended signals to differential signal or vice versa. On this EVM, they can be populated according to the application or the experiment. The VOCM pin of the device may be connected to the center-tap of the transformer, or maybe set via an external source such as Vref of a data converter. If the VOCM pin is not connected to an external source, it will be set at the center point of the power supply.
THS4140 EVM Bill of Materials Figure 2–5. Gain vs Phase Butterworth filter with multiple feedback frequency response. 10 8 6 Phase Gain – dB 4 2 0 Gain –2 –4 VIN = –1 dBm RL = 200 Ω Diff VCC = ±15 –8 –10 0.1 1 10 100 500 f – Frequency – MHz 2.8 THS4140 EVM Bill of Materials Table 2–1. THS4140 EVM Bill of Materials Ref. Description Size Qty. Manufacturer Part Number C1, C4, C5, C6 Capacitor, 0.1 µF, ceramic 0805 4 Murata GRM40–X7R104K25 C7, C8 Capacitor, 6.
THS4140 EVM Bill of Materials Table 2–1. THS4140 EVM Bill of Materials (continued) Ref. Description Size Qty. Manufacturer Part Number R3a, R3b Resistor, 374 Ω, 1% 0805 2 Digi-Key P374CTR-ND R4a, R4b Resistor, 0 Ω, 1% 1206 2 Digi-Key P0.0ECT-ND R6a, R6b Resistor, 402 Ω, 1% 0805 2 Digi-Key P402CTR-ND R11 Resistor, 10 kΩ, 1% 0805 1 Digi-Key P10.KCTR-ND R10, RX3, RX6 Resistor, 49.9 Ω, 1% 1206 3 Digi-Key P49.
Chapter 3 General High-Speed Amplifier Design Considerations The THS4140 EVM layout has been designed for use with high-speed signals and can be used as an example when designing PCBs incorporating the THS4140. Careful attention has been given to component selection, grounding, power supply bypassing, and signal path layout. Disregarding these basic design considerations could result in less than optimum performance of the THS4140 high-speed operational amplifier.
Finally, proper termination of all inputs and outputs must be incorporated into the layout. Unterminated lines, such as coaxial cable, can appear to be a reactive load to the amplifier. By terminating a transmission line with its characteristic impedance, the amplifier’s load then appears to be purely resistive, and reflections are absorbed at each end of the line. Another advantage of using an output termination resistor is that capacitive loads are isolated from the amplifier output.
