®

6

PCM67/69A

DISCUSSION OF

SPECIFICATIONS

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.

V

COM

R

NF

1.2mA

I

OUT

V

COM

(3.5V)

V

OUT

V

OUT

V

FIGURE 2. I/V Amplifier Circuit.

S/N RATIO

S/N ratio is defined as the ratio of full scale output and no input

noise level at BPZ point. The PCM67/69A is specified at

110dB typical with “IHF-A” filter.

LEVEL LINEARITY ERROR

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.

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

high level and low level input signals. This error is unadjustable

and is the most meaningful indicator of D/A converter accu-

racy for audio applications.

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

(1)

where n is the number of samples in one cycle of any given

PCM69A at each sampling point. THD can then be expressed

as

(2)

ε

1

n

E

L

(i )

+ E

Q

(i )





2

i

= 1

n

∑

THD

=

ε

rms

E

rms

=

1

n

E

L

(i )

+ E

Q

(i )





2

i

=1

n

∑

E

rms

× 100%

Analog

Out

Gain Error

Digital In

–FSR

(V

COM

= 3.5V)

+FSR

011...11

000...00

111...11

100...00

BPZ

BPZ – 1LSB

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.

ANALOG OUTPUT

ANALOG OUTPUT

DIGITAL INPUT

(VOLTAGE)

(CURRENT)

7FFFFF (HEX)

+FSR

–1.2mA

00003F (HEX)

BPZ

–0.6mA

FFFFFF (HEX)

BPZ – 1LSB

–0.59995mA

80003F (HEX)

–FSR

0mA

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.

Gain mismatch, channel-to-channel is defined as the differ-

ence in gain error between the left channel and right channel.

The output current range of PCM67 and PCM69A is 0mA to

1.2mA as shown in Table 1.

In the typical application, the non-inverting input of the

and PCM69A. Accordingly, the output voltage level at FSR

Figure 2.