HI5721_03 Datasheet, PDF (12/14 Pages) Intersil Corporation – 10-Bit, 125MSPS, High Speed D/A Converter

HI5721
a (mV)
t (ns)
GLITCH ENERGY = (a x t)/2
R1
PIN 25
(HI5721) _20K
PIN 20
(HI5721)
R2
20K
-5V
U1
2
3
4
-
+
8
6
1
R3
7 HA2705 _1K
+5V
R5
50
R4
240
-5V _U2
2
3
4
-
+
8
6
7 ^{1 HFA1100}
+5V
BIPOLAR
OUTPUT
R6 ^(±2.0V)
50
FIGURE 22. GLITCH ENERGY
Applications
Voltage Conversion of the Output
To convert the output current of the D/A converter to a
voltage, an amplifier should be used as shown in Figure 23
below. The DAC needs a 50Ω termination resistor on the
I_OUT pin to ensure proper settling. The HFA1110 has an
internal feedback resistor to compensate for high frequency
operation.
+5V
HI5721
DAC
20
I_OUT
50Ω
21
HFA1110
4
-
+
65
-5.2V
8
50Ω
FIGURE 23. HIGH SPEED CURRENT TO VOLTAGE CONVERSION
Bipolar Applications
To convert the output to a bipolar ±2.0V output swing the
following applications circuit is recommended. The
Reference can only provide 100µA of drive, so it must be
buffered to create the bipolar offset current needed to
generate -2.0V output with all bits ‘off’. The output current
must be converted to a voltage and then gained up and
offset to produce the proper swing. Care must be taken to
compensate for the output voltage swing and error.
Interfacing to the HSP45106 NCO-16
The HSP45106 is a 16-bit output, Numerically-Controlled
Oscillator (NCO). The HSP45106 can be used to generate
various modulation schemes for Direct Digital Synthesis
(DDS) applications. Figure 25 shows how to interface an
HI5721 to the HSP45106.
Interfacing to the HSP45102 NCO-12
The HSP45102 is a 12-bit output Numerically Controlled
Oscillator (NCO). The HSP45102 can be used to generate
various modulation schemes for Direct Digital Synthesis
FIGURE 24. BIPOLAR OUTPUT CONFIGURATION
(DDS) applications. Figure 26 shows how to interface an
HI5721 to the HSP45102.
This high level block diagram is that of a basic PSK
modulator. In this example the encoder generates the PSK
waveform by driving the Phase Modulation Inputs (P1, P0) of
the HSP45102. The P1-0 inputs impart a phase shift to the
carrier wave as defined in Table 2.
TABLE 2. PHASE MODULATION INPUT CODING
PHASE SHIFT
P1
P0
(DEGREES)
0
0
0
0
1
90
1
0
270
1
1
180
The 10 MSBs of the HSP45102 drive the 10-bit HI5721 DAC
which converts the NCO output into an analog waveform.
The output filter connected to the DAC can be tailored to
remove unwanted spurs for the desired carrier frequency.
The controller is used to load the desired center frequency
and control the HSP45102. The HI5721 coupled with the
HSP45102 make an inexpensive PSK modulator with
Spurious Free operation down to -76dBc.
12