THS4521_10 Datasheet, PDF (33/48 Pages) Texas Instruments – VERY LOW POWER, NEGATIVE RAIL INPUT, RAIL-TO-RAIL OUTPUT, FULLY DIFFERENTIAL AMPLIFIER

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Figure 79 shows the THS4521 and PCM4204 THD+N
versus frequency with no weighting at higher gains.
THS4521 and PCM4204 THD+N
vs FREQUENCY (No Weighting, at Higher Gains)
-95
-97
-99
-101
-103
G=5
G=2
-105 _{G = 1}
-107
-109
-111
-113
-115
0
100
1k
10 k 20 k
Frequency (Hz)
Figure 79. THS4521 and PCM4204: THD+N versus
Frequency with No Weighting at Higher Gains
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 op amps that are used to convert
single-ended inputs to differential to drive the ADC.
For testing, the op amp 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
THS4521
THS4522
THS4524
SBOS458D – DECEMBER 2008 – REVISED AUGUST 2010
EVM is configured for both differential inputs as
shown in Figure 60 and for single-ended input as
shown in Figure 61 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
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 80 shows the THD+N versus
frequency and Table 5 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.
-80
-82
-84
-86
-88
-90
-92
-94
-96
-98
-100
10
THS4521 and PCM3168 THD+N vs FREQUENCY
(No Weighting)
100
1k
Frequency (Hz)
10 k 20 k
Figure 80. THS4521 and PCM3168: THD+N versus
Frequency with No Weighting
Table 5. 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
PCM3168 Data
sheet (typ)
1 kHz
–93 dBc
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