Production Data

WM2148

WOLFSON MICROELECTRONICS LTD

PD Rev 1.1 February 2001

11

67

68

69

70

71

72

73

74

75

10

100

1000

10000

Signal Frequency [kHz] at -1dB

Figure 10 Signal to Noise Ratio at 3MSPS

67

68

69

70

71

72

73

74

75

10

100

1000

10000

Signal Frequency [kHz] at -1dB

Figure 11 Signal to Noise Ratio at 8MSPS

APPLICATION INFORMATION

DRIVING THE ANALOGUE INPUT

The WM2148 has a fully differential input. This is advantageous for signal to noise ratio, spurious

free dynamic range, and harmonic distortion. It is recommended that the analogue input pins IN+ and

IN- are connected as shown in Figure 12 below.

DIFFERENTIAL

ANALOGUE

INPUT

100pF

22 Ohms

100pF

22 Ohms

IN-

IN+

WM2148

Figure 12 Recommended Input Configuration

In this configuration, the ADC converts the difference

resistors and capacitors on the inputs decouple the driving source output from the ADC and also

serve as first order low pass filters to reduce out of band noise.

reference. The positive full-scale output is reached when

scale output is reached when

OUTPUT

-

- full scale

00

+ full scale

DIGITAL I/O

The digital outputs of the WM2148 are 3V CMOS compatible. In order to avoid current feedback

errors, the capacitive load on these outputs should be as low as possible (maximum 15pF). Adding

100

Ω series resistors on the digital outputs cam improve system performance by limiting the current

during output transitions (this reduces noise on the power supplies).