## AD8138ARZ-R7: Differential ADC Driver The **AD8138ARZ-R7** is a high-performance, low-distortion differential amplifier manufactured by Analog Devices. It is primarily designed to act as a driver for high-resolution Analog-to-Digital Converters (ADCs), converting single-ended signals to balanced differential signals. --- ### 1. Key Technical Specifications | Feature | Specification | | :--- | :--- | | **Type** | Differential Amplifier / ADC Driver | | **Configuration** | Single-ended to Differential or Differential to Differential | | **Bandwidth (-3 dB)** | 320 MHz (G = +1) | | **Slew Rate** | 1150 V/µs | | **Harmonic Distortion** | -94 dBc @ 5 MHz | | **Settling Time** | 16 ns to 0.01% | | **Supply Voltage Range** | 2.7 V to 12 V (Single or Dual Supply) | | **Package** | 8-Lead SOIC (Small Outline Integrated Circuit) | --- ### 2. Core Functionality and Pinout The AD8138 simplifies the transition from a standard signal source to a differential input ADC. It automatically balances the output and allows the user to set a common-mode voltage ($V_{OCM}$) to match the ADC's input requirements. #### Pin Configuration (8-Lead SOIC) 1. **-IN**: Inverting Input 2. **+IN**: Non-inverting Input 3. **VOCM**: Output Common-Mode Voltage Control 4. **V+**: Positive Supply Voltage 5. **+OUT**: Non-inverting Output 6. **-OUT**: Inverting Output 7. **V-**: Negative Supply Voltage (or Ground) 8. **NC**: No Connection --- ### 3. Application Use Cases * **ADC Driving**: Driving 12-bit to 16-bit ADCs (like the AD76xx series) in high-speed data acquisition. * **Single-Ended to Differential Conversion**: Eliminating the need for bulky transformers in signal chains. * **Differential Instrumentation**: Acting as a buffer for differential signals in noisy environments. * **Video Line Driver**: Low distortion makes it suitable for high-fidelity video transmission. --- ### 4. Part Number Breakdown Understanding the suffix for **AD8138ARZ-R7**: * **AD8138**: Base Model Number. * **A**: Temperature grade (usually -40°C to +85°C). * **R**: Package Type (SOIC). * **Z**: RoHS Compliant (Lead-free). * **R7**: Packaging format (7-inch Reel, typically containing 1,000 units). --- ### 5. Implementation Example To set the gain of the AD8138, external resistors ($R_f$ and $R_g$) are used, similar to a standard Op-Amp, but applied symmetrically. ```c // Calculation for Gain (G) // Gain = Rf / Rg // For a gain of 1: Rf = 499 Ohms; Rg = 499 Ohms; // Result: // Vout_dm = (Vin_p - Vin_n) * (Rf / Rg) ```