THS4521 Datasheet, PDF (45/65 Pages) Texas Instruments – VERY LOW POWER, NEGATIVE RAIL INPUT, RAIL-TO-RAIL OUTPUT, FULLY DIFFERENTIAL AMPLIFIER

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THS4521, THS4522, THS4524
SBOS458H – DECEMBER 2008 – REVISED JUNE 2015
9.2.1.2.1 Audio ADC Driver Performance: THS4521 and PCM3168 Combined Performance
The THS4521 is also tested as the drive amplifier for the PCM3168A ADC input. The PCM3168A is a high-
performance, single-chip, 24-bit, 6-in/8-out, audio coder/decoder (codec) with single-ended and differential
selectable analog inputs and differential outputs. The six-channel, 24-bit ADC employs a ΔΣ modulator and
supports 8-kHz to 96-kHz sampling rates and a 16-bit/24-bit width digital audio output word on the audio
interface. The eight-channel, 24-bit digital-to-analog converter (DAC) employs a ΔΣ modulator and supports 8-
kHz to 192-kHz sampling rates and a 16-bit/24-bit width digital audio input word on the audio interface. Each
audio interface supports I²S™, left-/right-justified, and DSP formats with 16-bit/24-bit word width. In addition, the
PCM3168A supports the time-division-multiplexed (TDM) format.. The PCM3168A provides flexible serial port
interface and many other advanced features. Refer to the PCM3168A product data sheet for more information.
The PCM3168A EVM is used to test the audio performance of the THS4521 as a drive amplifier. The standard
PCM3168A EVM is provided with OPA2134 operational amplifiers that are used to convert single-ended inputs to
differential to drive the ADC. For testing, the operational amplifier output series resistors are removed from one of
the channels and a THS4521, mounted on its standard EVM, is connected to the ADC inputs via short coaxial
cables. The THS4521 EVM is configured for both differential inputs as shown in Figure 91 and for single-ended
input as shown in Figure 92 with 1-kΩ resistors for R_F and R_G, and 24.9-Ω resistors in series with each output to
isolate the outputs from the reactive load of the coaxial cables. To limit the noise from the external EVM and
cables, a 2.7-nF capacitor is placed differentially across the PCM3168A inputs. The THS4521 is operated with a
single-supply +5-V supply so the output common-mode of the THS4521 defaults to +2.5 V as required at the
input of the PCM3168A. The PCM3168A EVM is configured and operated as described in the PCM3168AEVM
User's Guide. The ADC was tested with an external THS4521 EVM with both single-ended input and differential
inputs. In both configurations, the results are the same. Figure 81 shows the THD+N versus frequency and
Table 10 compares the result to the PCM3168 data sheet typical specification at 1 kHz. Both graphs show that it
makes an excellent drive amplifier for this ADC. Note: a 2700 series Audio Analyzer from Audio Precision is
used to generate the input signals to the THS4521 and to analyze the digital data from the PCM3168.
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THS4521 and PCM3168 THD+N vs FREQUENCY
(No Weighting)
100
1k
Frequency (Hz)
10 k 20 k
Figure 81. THS4521 and PCM3168: Thd+N Versus Frequency With No Weighting
Table 10. 1-kHz AC Analysis: Test Circuit vs PCM3168 Data Sheet Typical Specifications (F_S = 48 kSPS)
Configuration
Tone
THD+N
THS4521 and PCM3168
1 kHz
–92.6 dBc
PCM3168A Data sheet (typ)
1 kHz
–93 dBc
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Product Folder Links: THS4521 THS4522 THS4524