DC1858A Analog Devices

DEMO MANUAL DC1858A Low Noise, Low Distortion Sine Wave Generator for Testing ADC Demo Boards Description Demonstration circuit 1858A is a low noise, low distortion AN132. The DC1858A has 5V and 12V outputs that can sine wave generator designed to be used in conjunction be used to provide power for the ADC demo board under with Linear Technology 16-bit and 18-bit ADC demo boards. test and the DC1216A low jitter clock source if required. The DC1858A combined with the DC1216A, an ADC demo Functionally, this board uses a Wien bridge oscillator that board and a high speed USB controller (DC718 or DC890) has been level shifted to match the input range of 0V to 5V form a complete ADC evaluation system when used with 16-bit and 18-bit Linear Technology ADC demo boards. The LTCs PScope software. default oscillator output level is 0.5V to 4.5V. The output frequency is 2kHz. The output level and frequency can Design files for this circuit board are available at be adjusted by changing a few resistors and capacitors. DEMO MANUAL DC1858A Quick s Dp Use the connection diagram of Figure 1. Connect the ADC is located at the top of the PScope window. Remember demo board to a DC718 or DC890 USB high speed data that to calculate the true SNR, the F1 amplitude has to be collection board (DC718 or DC890 will be determined by added back to the SNR that PScope displays. the ADC demo board being tested). Then, connect the DC718 or DC890 to a host PC with a standard USB A/B IF THE OSCILLATOR DOESNT START cable. Apply 12V from the DC1858A power outputs (see Use the supplied non-conductive screwdriver to adjust Figure 2) to the plus or terminals of the ADC demo board the potentiometer through the opening in the box until a as required. Connect the SINE OUT (see Figure 3) of the steady 2kHz sine wave with an amplitude of approximately DC1858A to the analog input of the ADC demo board. (The 4.5V is observed. The oscillator has three states, nor- P-P SINE OUT output is designed to drive a high impedance mal oscillation, oscillation with modulated amplitude, input. Do not use this to drive 50 inputs.) Connect a low and no oscillation. It takes only a small change in the jitter clock to the clock input of the demo board. DC1858A potentiometer to go through all three states so adjust the has a 5V output supply available to power the DC1216A potentiometer slowly. low jitter clock source if desired. (See Figure 1 for con- nection diagram. A twisted pair or shielded cable from the DC1858A to the DC1216A power pins is recommended to minimize interference from the AC adapter.) Plug in the provided AC adapter. Download and run the PScope software from www.linear. com/designtools/software. Complete software documentation is available from the Help menu. Updates can be downloaded from the Tools menu. Check for updates periodically as new features may be added. The PScope software should recognize the ADC demo Figure 2. DC1858A Rear Panel board and configure itself automatically. Set the sample rate in Msps to what is appropriate for the ADC used. The sample size should be set to 32768 for 16-bit ADCs or 131072 for 18-bit ADCs and above. If synchronous sampling is not used set the window to Blkmn-Harris 92dB, otherwise select None. Sample rate, sample size and window are located in the right hand center section of the PScope window. Click the Collect button to begin acquiring data. The Collect button then changes to Pause, which can be clicked to stop data acquisition. F1 should read approximately 2kHz and F1 amplitude should read approximately 1dBFS. To get the best SNR performance it is recommended to turn Figure 3. DC1858A Front Panel on power averaging. The power averaging (MAVG) button dc1858af 2 ure roce tart