ML2036

7

FUNCTIONAL DESCRIPTION

The ML2035 is composed of a programmable frequency

generator, a sine wave generator, a crystal oscillator, and a

serial digital interface. The ML2036 frequency and sine

wave generator functional block diagram is shown in

Figure 4.

PROGRAMMABLE FREQUENCY GENERATOR

The programmable frequency generator produces a digital

output whose frequency is determined by a 16-bit digital

word.

The frequency generator is composed of a phase

stored in the data latch is added to the phase accumulator

every 4 cycles of CLK IN. The frequency of the analog

output is equal to the rate at which the accumulator

overflows and is given by the equation:

f

fD

D

OUT

CLKIN

DEC

=

×−

15

0

2

23

05

(1)

The frequency resolution and the minimum frequency are

the same and is given by the following equation:

∆f

f

MIN

CLKIN

=

2

23

(2)

Lower frequencies are obtained by using a lower input

clock frequency.

Due to the phase quantization nature of the frequency

generator, spurious tones can be present in the output

range of –55dB relative to fundamental. The energy from

these tones is included in the signal to noise + distortion

specification. The frequency of these tones can be very

close to the fundamental. Therefore, it is not practical to

filter them out.

SINE WAVE GENERATOR

The sine wave generator is composed of a sine look-up

table, a DAC, and an output smoothing filter. The sine

look-up table is addressed by the phase accumulator. The

DAC is driven by the output of the look-up table and

generates a staircase representation of a sine wave.

The output filter smoothes the analog output by removing

the high frequency sampling components. The resultant

harmonic distortion components at least 45dB below the

fundamental.

generated from an external voltage. With the GAIN input

equal to a logic "1", the sine wave peak-to-peak voltage is

voltage swing is limited to no closer than 1.5V to either

is referenced to AGND.

The analog section is designed to operate over a range

from DC to 50kHz. Due to slew rate limitations, the peak-

slew rate limitations mentioned above are not exceeded.

peak output voltage and is specified as:

V

V

OS MAX

OUT P P

05

05

=±

+









−

25

100

.

(3)

VmV

OS MAX

+

25 25

100

50

..

CRYSTAL OSCILLATOR

The crystal oscillator generates an accurate reference

clock for the programmable frequency generator. The

internal clock can be generated with a crystal or external

clock.

If a crystal is used, it must be placed between CLK IN and

DGND of the ML2036. An on-chip crystal oscillator will

then generate the internal clock. No other external

capacitors or components are required. The crystal should

be a parallel-resonant type with a frequency between

3MHz to 12.4MHz. It should be placed physically as close

as possible to the CLK IN and DGND.

An external clock can drive CLK IN directly if desired. The

frequency of this clock can be anywhere between 0 and

12MHz.

SCK

SID

LATI

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Figure 5. Serial Interface Timing.