データシートサーチシステム |
|
AD8005 データシート(PDF) 11 Page - Analog Devices |
|
AD8005 データシート(HTML) 11 Page - Analog Devices |
11 / 16 page Data Sheet AD8005 Amp 1 has its +input driven with the ac-coupled input signal while the +input of Amp 2 is connected to a bias level of +2.5 V. Thus the −input of Amp 2 is driven to virtual +2.5 V by its output. Therefore, Amp 1 is configured for a noninverting gain of five, (1 + RF1/RG), because RG is connected to the virtual +2.5 V of the –input of Amp 2. When the +input of Amp 1 is driven with a signal, the same signal appears at the −input of Amp 1. This signal serves as an input to Amp 2 configured for a gain of −5, (−RF2/RG). Thus the two outputs move in opposite directions with the same gain and create a balanced differential signal. This circuit can be simplified to create a bipolar in/bipolar out single-ended to differential converter. Obviously, a single supply is no longer adequate and the −VS pins must now be powered with −5 V. The +input to Amp 2 is tied to ground. The ac coupling on the +input of Amp 1 is removed and the signal can be fed directly into Amp 1. LAYOUT CONSIDERATIONS In order to achieve the specified high-speed performance of the AD8005, the user must be attentive to board layout and component selection. Proper RF design techniques and selection of components with low parasitics are necessary. The printed circuit board (PCB) must have a ground plane that covers all unused portions of the component side of the board. This provides a low impedance path for signals flowing to ground. Remove the ground plane from the area under and around the chip (leave about 2 mm between the pin contacts and the ground plane). This helps to reduce stray capacitance. If both signal tracks and the ground plane are on the same side of the PCB, also leave a 2 mm gap between ground plane and track. Figure 34. Inverting and Nonconverting Configurations Chip capacitors have low parasitic resistance and inductance and are suitable for supply bypassing (see Figure 34). Make sure that one end of the capacitor is within 1/8 inch of each power pin with the other end connected to the ground plane. An additional large (0.47 µF − 10 µF) tantalum electrolytic capacitor must also be connected in parallel. This capacitor supplies current for fast, large signal changes at the output. It must not necessarily be as close to the power pin as the smaller capacitor. Locate the feedback resistor close to the inverting input pin in order to keep the stray capacitance at this node to a minimum. Capacitance variations of less than 1.5 pF at the inverting input significantly affect high-speed performance. Use stripline design techniques for long signal traces (that is, greater than about 1 inch). Striplines must have a characteristic impedance of either 50 Ω or 75 Ω. For the stripline to be effective, correct termination at both ends of the line is necessary. Table 5. Typical Bandwidth vs. Gain Setting Resistors Gain RF RG RT Small Signal −3 dB BW (MHz), VS = ±5 V −1 1.49 kΩ 1.49 kΩ 52.3 120 MHz −10 1 kΩ 100 Ω 100 Ω 60 MHz +1 2.49 kΩ ∞ 49.9 Ω 270 MHz +2 2.49 kΩ 2.49 kΩ 49.9 Ω 170 MHz +10 499 Ω 56.2 Ω 49.9 Ω 40 MHz INCREASING FEEDBACK RESISTORS Unlike conventional voltage feedback op amps, the choice of feedback resistor has a direct impact on the closed-loop bandwidth and stability of a current feedback op amp circuit. Reducing the resistance below the recommended value makes the amplifier more unstable. Increasing the size of the feedback resistor reduces the closed-loop bandwidth. Figure 35. Saving Power by Increasing Feedback Resistor Network In power-critical applications where some bandwidth can be sacrificed, increasing the size of the feedback resistor yields significant power savings. A good example of this is the gain of +10 case. Operating from a bipolar supply (±5 V), the quiescent current is 475 µA (excluding the feedback network). The recom- mended feedback and gain resistors are 499 Ω and 56.2 Ω respectively. In order to drive an rms output voltage of 2 V, the output must deliver a current of 3.6 mA to the feedback network. Increasing the size of the resistor network by a factor of 10, as shown in Figure 35, reduces this current to 360 µA; however, the closed loop bandwidth decreases to 20 MHz. C1 0.01µF C2 0.01µF C3 10µF C4 10µF INVERTING CONFIGURATION VIN RG RT RF RO VOUT +VS –VS C1 0.01µF C2 0.01µF C3 10µF C4 10µF VIN RG RT RF RO NONINVERTING CONFIGURATION VOUT +VS –VS 360µA (rms) VOUT 2V (rms) +5V 4.99kΩ 562Ω –5V AD8005 VIN 0.2V (rms) QUIESCENT CURRENT 475µA (MAX) Rev. B | Page 11 of 16 |
同様の部品番号 - AD8005_15 |
|
同様の説明 - AD8005_15 |
|
|
リンク URL |
プライバシーポリシー |
ALLDATASHEET.JP |
ALLDATASHEETはお客様のビジネスに役立ちますか? [ DONATE ] |
Alldatasheetは | 広告 | お問い合わせ | プライバシーポリシー | リンク交換 | メーカーリスト All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |