On Tue, 13 Jan 2015 19:18:37 -0500, Phil Hobbs
wrote:
On 1/13/2015 3:17 PM, Jim Thompson wrote:
Anyone have ideas regarding how to implement a voltage-variable phase
shifter useable at 210MHz?
...Jim Thompson
I've used a variation of the normal op amp all-pass filter for this,
except with a high frequency diff amp:
*---------------*
| |
0-----*-----RRRR-------*----| |
| | | |
| R | Diff amp |
| Gain of 0.5 R | |
| R | *-----Out
| | | |
| | | |
| GND | |
| | |
*-----RRRR--*----*----| |
| | | |
| | *---------------*
| L
| L
| L
| L
L |
L |
L |
L --- Varactor
| ^
| |
| *---RRRR----0 V_phi |
| |
| CCC
| CCC big C
| |
GND GND
You pick the voltage divider to have a gain of 0.5; the series L
resonates the varactor just past the low-voltage end of V_phi;
and the shunt inductor resonates the series combination just past the
high end of V_phi. You can get about 150 degrees in one stage, with
linearity of +- a few degrees. Good medicine.
Cheers
Phil Hobbs
That's what the customer is currently using except for a capacitance
multiplier made with an AD834(?)
...Jim Thompson
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