Analog Smoothing Filter & Programmable Gain Amp; Differential Output Amplifier - Analog Devices adsp-2100 Manual

8 Analog Interface
Figure 8.2 shows the frequency response of the IIR low pass filter.
Passband ripple is ±0.2 dB for the combined effects of the DAC's
digital filters (i.e. high pass filter and IIR low pass of the interpolation
filter) in the 300–3400 Hz passband.
8.3.1.3 Analog Smoothing Filter & Programmable Gain Amplifier
The DAC's programmable gain amplifier (PGA) can be used to adjust
the output signal level by –15 dB to +6 dB. This gain is selected by bits
2-4 (OG0, OG1, OG2) of the of the ADSP-21msp58/59's analog control
register.
The DAC's analog smoothing filter consists of a 2nd-order Sallen-Key
continuous-time filter and a 3rd-order switched capacitor filter. The
Sallen-Key filter has a 3 dB point at approximately 25 kHz.
8.3.2

Differential Output Amplifier

The ADSP-21msp58/59's analog output signal (VOUT – VOUT ) is
P N
produced by a differential amplifier. The differential amplifier meets
≥ 2 kΩ) and has a
specifications for loads greater than 2 kΩ (R
L
maximum differential output voltage swing of ±3.156 V peak-to-peak
(3.17 dBm0). The DAC will drive loads smaller than 2 kΩ, but with
degraded performance.
The output signal is dc-biased to the on-chip voltage reference (V )
REF
and can be ac-coupled directly to a load or dc-coupled to an external
amplifier. Refer to "Analog Output" in the "Design Considerations"
section of this chapter for more information.
– VOUT outputs must be used as a differential signal,
The VOUT
P N
otherwise performance will be severely degraded. Do not use either
pin as a single-ended output.
8 – 8