AD835
Figure 22 shows a frequency doubler which overcomes this limi-
tation and provides a relatively constant output over a moder-
ately wide frequency range, determined by the time-constant C1
and R1. The voltage applied to the X- and Y-inputs are exactly
in quadrature at a frequency f = 1/2
πC1R1
and their ampli-
tudes are equal. At higher frequencies, the X-input becomes
smaller while the Y-input increases in amplitude; the opposite
happens at lower frequencies. The result is a double frequency
output, centered on ground, whose amplitude of 1 V for a 1 V
input varies by only 0.5% over a frequency range of
±
10%. Be-
cause there is no “squared” dc component at the output, sud-
den changes in the input amplitude do not cause a “bounce” in
the dc level.
V
G
C1
VOLTAGE
OUTPUT
8
X1
X1
Y1
1
7
X2
Y2
2
6
VP
VN
3
5
W
R2
97.6Ω
Z
4
0.022 (0.558)
0.014 (0.356)
0.100
(2.54)
BSC
0.070 (1.77)
0.045 (1.15)
SEATING
PLANE
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
8-Pin Plastic DIP
(N Package)
C1903a–3–12/94
0.325 (8.25)
0.300 (7.62)
0.060 (1.52)
0.015 (0.38)
0.195 (4.95)
0.115 (2.93)
0.015 (0.381)
0.008 (0.204)
8
PIN 1
1
5
0.280 (7.11)
0.240 (6.10)
4
0.430 (10.92)
0.348 (8.84)
0.210
(5.33)
MAX
0.160 (4.06)
0.115 (2.93)
+5V
0.130
(3.30)
MIN
AD835
R1
–5V
R3
301Ω
8-Pin Plastic SOIC
(R Package)
8
5
0.1574 (4.00)
0.1497 (3.80)
Figure 22. Broadband “Zero-Bounce” Frequency Doubler
This circuit is based on the identity
cos
θ
sin
θ =
1
sin 2θ
2
PIN 1
1
4
0.2440 (6.20)
0.2284 (5.80)
( 7)
0.0098 (0.25)
0.0040 (0.10)
0.1968 (5.00)
0.1890 (4.80)
0.102 (2.59)
0.094 (2.39)
0.0500
(1.27)
BSC
0.0192 (0.49)
0.0138 (0.35)
8
°
0
°
0.0196 (0.50)
x 45
°
0.0099 (0.25)
At
ω
O
= 1/C1R1, the X input leads the input signal by 45° (and
is attenuated by
√2,
while the Y input lags the input signal by
45°, and is also attenuated by
√2.
Since the X and Y inputs are
90° out of phase, the response of the circuit will be
0.0098 (0.25)
0.0075 (0.19)
0.0500 (1.27)
0.0160 (0.41)
1
E
E
E
2
W
=
(sin
ωt
– 45° )
(sin
ωt +
45° )
=
(sin 2ωt )
(8)
2U
U
2
2
which has no dc component, R2 and R3 are included to restore
the output to 1 V for an input amplitude of 1 V (the same gain
adjustment as mentioned earlier). Because the voltage across the
capacitor, C1, decreases with frequency, while that across the
resistor, R1, increases, the amplitude of the output varies only
slightly with frequency. In fact, it is only 0.5% below its full
value (at its center frequency
ω
Ο
= 1/C1R1) at 90% and 110%
of this frequency.
–8–
REV. A
PRINTED IN U.S.A.
AD [ ANALOG DEVICES ]
