®

PCM54/55

4

DISCUSSION OF

SPECIFICATIONS

The PCM54 and PCM55 are specified to provide critical

performance criteria for a wide variety of applications. The

most critical specifications for a D/A converter in audio

applications are total harmonic distortion, differential linear-

ity error, bipolar zero error, parameter shifts with time and

temperature, and settling time effects on accuracy.

The PCM54 and PCM55 are factory-trimmed and tested for

all critical key specifications.

The accuracy of a D/A converter is described by the transfer

function shown in Figure 1. Digital input to analog output

relationship is shown in Table I. The errors in the D/A

converter are combinations of analog errors due to the linear

circuitry, matching and tracking properties of the ladder and

scaling networks, power supply rejection, and reference

errors. In summary, these errors consist of initial errors

including gain, offset, linearity, differential linearity, and

power supply sensitivity. Gain drift over temperature rotates

the line (Figure 1) about the bipolar zero point and offset

drift shifts the line left or right over the operating tempera-

ture range. Most of the offset and gain drift with temperature

or time is due to the drift of the internal reference zener

diode. The converter is designed so that these drifts are in

opposite directions. This way, the bipolar zero voltage is

virtually unaffected by variations in the reference voltage.

DIGITAL INPUT CODES

The PCM54 and PCM55 accept complementary digital

input codes in any of three binary formats (CSB, unipolar; or

COB, bipolar; or CTC, Complementary Two’s Comple-

ment, bipolar). See Table II.

Gain

Drift

Offset

Drift

Bipolar

Zero

–FSR/2

(+FSR/2) –1LSB

Analog Output

0000…0000

0000…0001

0111…1101

0111…1110

0111…1111

1000…0000

1000…0001

1111…1110

1111…1111

All Bits

On

* See Table I for digital code definitions.

FIGURE 1. Input vs Output for an Ideal Bipolar D/A

Converter.

ANALOG OUTPUT

Digital

Complementary

Complementary

Complementary

Input

Straight Binary

Offset Binary

Two’s Complement

Codes

(CSB)

(COB)

+Full Scale

+Full Scale

–1LSB

+1/2 Full Scale

Bipolar Zero

–Full Scale

+1/2 Full Scale

–1LSB

+Full Scale

–1LSB

Zero

–Full Scale

Bipolar Zero

NOTE: (1) Invert the MSB of the COB code with an external inverter to obtain

CTC code.

TABLE II. Digital Input Codes.

BIPOLAR ZERO ERROR

Initial Bipolar Zero (BPZ) error (Bit 1 “ON” and all other

bits “OFF”) is the deviation from 0V out and is factory-

trimmed to typically

±10mV at +25°C.

DIFFERENTIAL LINEARITY ERROR

Differential Linearity Error (DLE) is the deviation from an

ideal 1LSB change from one adjacent output state to the

next. DLE is important in audio applications because exces-

sive DLE at bipolar zero (at the “major carry”) can result in

audible crossover distortion for low level output signals.

Initial DLE on the PCM54 and PCM55 is factory-trimmed

to typically

±0.001% of FSR. This error is adjustable to zero

using the circuit shown in the connection diagram (PCM54

only).

VOLTAGE OUTPUT MODE

Analog Output

Bipolar

Digital Input Code

16-Bit

15-Bit

14-Bit

16-Bit

15-Bit

14-Bit

One LSB

(

µV)

91.6

183

366

91.6

183

366

(V)

+5.99991

+5.99982

+5.99963

+2.99991

+2.99982

+2.99963

(V)

0

0

0

–3.0000

–3.0000

–3.0000

CURRENT OUTPUT MODE

Analog Output

Unipolar

Bipolar

Digital Input Code

16-Bit

15-Bit

14-Bit

16-Bit

15-Bit

14-Bit

One LSB

(

µA)

0.031

0.061

0.122

0.031

0.061

0.122

(mA)

–1.99997

–1.99994

–1.99988

–0.99997

–0.99994

–0.99988

(mA)

0

0

0

+1.00000

+1.00000

+1.00000

TABLE I. Digital Input to Analog Output Relationship.

Not Recommended For New Designs