DISCUSSION OF
SPECIFICATIONS
VOUT = 1.2mA • RNF
The PCM67 and PCM69A are specified to provide critical
performance criteria for a variety of applications. The accu-
racy of a D/A converter is described by the transfer function
shown in Figure 1.
VOUT
VCOM
RNF
1.2mA
IOUT
Digital In
+FSR
VOUT
011...11
VCOM
Gain Error
(3.5V)
FIGURE 2. I/V Amplifier Circuit.
000...00
S/N RATIO
Analog
Out
111...11
S/Nratioisdefinedastheratiooffullscaleoutputandnoinput
noise level at BPZ point. The PCM67/69A is specified at
110dB typical with “IHF-A” filter.
BPZ
BPZ – 1LSB
100...00
–FSR
LEVEL LINEARITY ERROR
(VCOM = 3.5V)
Level linearity error is defined as the deviation of actual
analog output level from digital input level. PCM67/69A is
specified at 1dB typical at –90dB output level. The 0.5LSB
quantization error at –90dB of 16-bit conversion is equal to
+1.94dB, –2.5dB.
FIGURE 1. Transfer Performance.
DIGITAL INPUT CODE
The PCM67/69A accepts Binary Two’s Complement (BTC)
digital input code (MSB FIRST).The relationship of digital
input to analog output is shown in Table 1.
TOTAL HARMONIC DISTORTION
THD is a key parameter in audio applications, THD is a
measure of the magnitude and distribution of the linearity
error, differential linearity error, and noise, as well as quanti-
zation error. To be useful, THD should be specified for both
highlevelandlowlevelinputsignals.Thiserrorisunadjustable
and is the most meaningful indicator of D/A converter accu-
racy for audio applications.
ANALOG OUTPUT
(VOLTAGE)
ANALOG OUTPUT
(CURRENT)
DIGITAL INPUT
7FFFFF (HEX)
00003F (HEX)
FFFFFF (HEX)
80003F (HEX)
+FSR
BPZ
BPZ – 1LSB
–FSR
–1.2mA
–0.6mA
–0.59995mA
0mA
THD is defined as the ratio of the square root of the sum of the
squares of the values of the harmonics to the value of the
fundamental input frequency and is expressed in percent or
dB. The rms value of the PCM67/69A error referred to the
input can be shown to be
TABLE I. Digital Code and Analog Out.
GAIN ERROR AND GAIN MISMATCH,
CHANNEL-TO-CHANNEL
Gain error is defined as deviation of the output current span
from the ideal span of 1.2mA (FSR) on each channel. Gain
error of PCM67/69A is typically ±3% of FSR.
n
2
1
n
(1)
ε rms
=
EL (i) + EQ(i)
∑
i = 1
Gain mismatch, channel-to-channel is defined as the differ-
ence in gain error between the left channel and right channel.
where n is the number of samples in one cycle of any given
sine wave, EL(i) is the linearity error of the PCM67 or
PCM69A at each sampling point. THD can then be expressed
as
THE RELATIONSHIP OF VCOM AND I/V OUT
The output current range of PCM67 and PCM69A is 0mA to
1.2mA as shown in Table 1.
n
2
In the typical application, the non-inverting input of the
external I/V op amp is connected to the VCOM pin of PCM67
and PCM69A. Accordingly, the output voltage level at FSR
after I/V conversion is VCOM voltage (+3.5V) as shown in
Figure 2.
1
n
EL (i) + EQ (i)
∑
εrms
i =1
THD =
=
× 100%
E
Erms
rms
(2)
where Erms is the rms signal-voltage level.
®
PCM67/69A
6
BB [ BURR-BROWN CORPORATION ]
